@inproceedings{KuehhornGolze, author = {K{\"u}hhorn, Arnold and Golze, Mark}, title = {An Improved Sandwich Theory for a Better Prediction of the Wrinkling Phenomenon}, series = {Proceedings of the Fifth World Congress on Computational Mechanics, Vienna, Austria, July 7 - 12, 2002, held at Vienna University of Technology}, booktitle = {Proceedings of the Fifth World Congress on Computational Mechanics, Vienna, Austria, July 7 - 12, 2002, held at Vienna University of Technology}, address = {Vienna}, isbn = {3-9501554-0-6}, abstract = {An advanced design of sandwichstructures does not only require the knowledge of the global stress- and deformation behavior, but also the knowledge of the local effects, such as load singularities and the loss of stability caused by the short wave wrinkling of one (bending) or both (pressure) sandwich skins.Based on the nonlinear theory for sandwich shells with seven kinematic degrees of freedom, introduced from K{\"u}hhorn and Schoop an improved theory for plane sandwich shells with eight degrees of freedom will be presented, enabling a much better representation of the sandwich core behavior.Due to consideration of quadratic core thickness and linear core shear strain as well as longitudinal core deformation an improved prediction of the wrinkling behavior is succeeded even for thick cores and thin skins.The kinematic quantities as well as the nonlinear-differential equations and the simplified equations of first order theory resulting from them are given.Finally applying the well known classical problems of stability loaded by pressure and bending, the efficiency of this 8 DOF-theory ist demonstrated. A comparison with a detailed finite element (plain strain) calculation shows the high quality of these results.The presented sandwich theory characterized by eight degrees of freedom enables the calculation of nearly all essential sandwich phenomena even for thick cores.}, language = {en} } @article{KuehhornBeirow, author = {K{\"u}hhorn, Arnold and Beirow, Bernd}, title = {Schwingungsreduzierung an der Antriebseinheit eines Ultraleichtflugzeuges}, series = {Forum der Forschung}, volume = {6}, journal = {Forum der Forschung}, edition = {14}, issn = {0947-6989}, pages = {105 -- 108}, abstract = {Auf Grund der im Rahmen eines Testfluges subjektiv durch den Piloten festgestellten hohen Schwingungsamplituden wird das dynamische Verhalten eines Ultraleichtflugzeugmotors inklusive der Motoraufh{\"a}ngung untersucht. Hierin wir der numerische Teil der Untersuchun-gen durch eine finite Elemente Simulation abgedeckt, in deren Rahmen die wesentlichen Ei-genschwingformen der Antriebseinheit samt Motortr{\"a}ger identifiziert wurden. Erg{\"a}nzend mit den Ergebnissen einer experimentellen Modalanalyse und Betriebsschwingungsmessungen konnten wesentliche Informationen gewonnen werden, aus denen als Maßnahme zur Schwin-gungsreduzierung die Erh{\"o}hung der Schwungradmasse abgeleitet wurde.}, language = {de} } @inproceedings{KuehhornGolze, author = {K{\"u}hhorn, Arnold and Golze, Mark}, title = {Thickness flexible theory with generalized core warping for plane sandwich-structures}, abstract = {An advanced design of sandwichstructures does not only require the knowledge of the global stress- and deformation behavior, but also the knowledge of the local effects, such as load singularities and the loss of stability caused by the short wave wrinkling of one (bending) or both (pressure) sandwich skins.Based on the nonlinear theory for sandwich shells with seven kinematic degrees of freedom, introduced from K{\"u}hhorn and Schoop an improved theory for plane sandwich shells with eight degrees of freedom (position vector r, director d, and intensity factors az1, az2 for including core flexibility) will be presented, enabling a much better representation of the sandwich core behavior.Due to consideration of quadratic core thickness and linear core shear strain as well as longitudinal core deformation an improved prediction of the wrinkling behavior is succeeded even for thick cores and thin skins.The kinematic quantities as well as the nonlinear-differential equations achieved from the principle of virtual work and the simplified equations of first order theory resulting from them are given.Finally applying the well known classical problems of stability loaded by pressure and bending, the efficiency of this 8 DOF-theory is demonstrated. A comparison with a detailed finite element (plain strain) calculation shows the high quality of these results.The presented sandwich theory characterized by eight kinematic degrees of freedom is valid for arbitrary displacements, rotations and moderat strains enables the calculation of nearly all essential sandwich phenomena even for thick cores.}, language = {en} } @inproceedings{GolzeKuehhorn, author = {Golze, Mark and K{\"u}hhorn, Arnold}, title = {CFK-/GFK-Auslegung am Beispiel eines Modellfl{\"u}gels}, series = {Tagungsband, 14. deutschsprachiges ABAQUS Anwendertreffen, 23. - 24. September 2002 in Wiesbaden}, booktitle = {Tagungsband, 14. deutschsprachiges ABAQUS Anwendertreffen, 23. - 24. September 2002 in Wiesbaden}, publisher = {ABACOM Software GmbH}, address = {Aachen}, abstract = {{\"O}konomische und {\"o}kologische Bed{\"u}rfnisse verlangen von modernen Konstruktionen sowohl eine hochintegrative Bauweise als auch eine massive Gewichtseinsparung. Dies f{\"u}hrt zu neuen Leichtbaukonstruktionen mit einem stetig zunehmenden Anteil an Faserverbundl{\"o}sungen. Die hierbei er{\"o}ffnete M{\"o}glichkeit, kraftfluß- und beanspruchungsgerecht auszulegen, erschließt sich erst vollst{\"a}ndig durch die sichere Anwendung moderner FE-Programme wie beispielsweise ABAQUS. Nutzt man dar{\"u}ber hinaus die M{\"o}glichkeit der flexiblen Script-Programmierung, so lassen sich wirkungsvolle Effizienzsteigerungen durch die gezielte Erstellung spezifischer Eingabemen{\"u}s und Ausgaberoutinen erreichen. Dieser Beitrag veranschaulicht an Hand eines ausgef{\"u}hrten und getesteten CFK-Modellfl{\"u}gels unter Biegebeanspruchung, die Vorgehensweise bei Verwendung von ABAQUS und der Script-Sprache Python.}, language = {de} } @inproceedings{StudenerKuehhorn, author = {Studener, Johannes and K{\"u}hhorn, Arnold}, title = {FE-Untersuchungen zum dynamischen Verhalten einer integralen Verdichterschaufelscheibe neuer Generation}, series = {Tagungsband, 14. deutschsprachiges ABAQUS Anwendertreffen, 23. - 24. September 2002 in Wiesbaden}, booktitle = {Tagungsband, 14. deutschsprachiges ABAQUS Anwendertreffen, 23. - 24. September 2002 in Wiesbaden}, publisher = {Abacom Software GmbH}, address = {Aachen}, abstract = {Eigenwertanalyse eines FE-Modells unter Ber{\"u}cksichtigung des Kopplungsverhaltens zwischen Schaufel und Scheibe}, language = {de} } @inproceedings{BeirowKuehhorn, author = {Beirow, Bernd and K{\"u}hhorn, Arnold}, title = {Schwingungsreduzierung an der Antriebseinheit eines Ultraleichtflugzeuges : Beitrag Deutscher Luft- und Raumfahrtkongress Stuttgart 2002}, abstract = {Initiiert durch die im Rahmen eines Testfluges subjektiv durch den Piloten festgestellten hohen Schwingungsamplituden wird das dynamische Verhalten eines Ultraleichtflugzeugmotors inklusive der Motoraufh{\"a}ngung untersucht. Hierin wir der numerische Teil der Untersuchungen durch eine finite Elemente Simulation abgedeckt, in deren Rahmen die wesentlichen Eigenschwingformen der Antriebseinheit samt Motortr{\"a}ger identifiziert wurden. Erg{\"a}nzend mit den Ergebnissen einer experimentellen Modalanalyse und Betriebsschwingungsmessungen konnten wesentliche Informationen gewonnen werden, aus denen als Maßnahme zur Schwin-gungsreduzierung die Erh{\"o}hung der Schwungradmasse abgeleitet wurde.}, language = {de} } @inproceedings{BeirowKuehhornOsterrieder, author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Osterrieder, Peter}, title = {Windinduzierte Schwingungserregung von Fernmeldet{\"u}rmen}, series = {Fluid-Struktur-Wechselwirkung, Tagung Wiesloch, 11. und 12. Juni 2002}, booktitle = {Fluid-Struktur-Wechselwirkung, Tagung Wiesloch, 11. und 12. Juni 2002}, publisher = {VDI-Verlag}, address = {D{\"u}sseldorf}, isbn = {3-18-091682-6}, pages = {407 -- 422}, abstract = {Vorstellung eines stochastischen Verfahrens zur Berechnung windinduzierter Querschwingungen, Pr{\"a}sentation am Beispiel des Fernmeldeturmes Cottbus}, language = {de} } @article{KuehhornBeirowStudener, author = {K{\"u}hhorn, Arnold and Beirow, Bernd and Studener, Johannes}, title = {Messtechnische Beanspruchungsuntersuchungen beim Transport von Glasr{\"o}hrenkollektoren}, language = {de} } @article{KuehhornKlaukeGolze, author = {K{\"u}hhorn, Arnold and Klauke, Thomas and Golze, Mark}, title = {Simulation und Verifikation der sukzessiven Bruchabfolge eines CFK-Bauteils mittels neuartiger Bruchkriterien}, language = {de} } @article{KuehhornBeirowKlaukeetal., author = {K{\"u}hhorn, Arnold and Beirow, Bernd and Klauke, Thomas and Golze, Mark}, title = {Simulation der Mistuningeffekte von Hochdruckverdichter-Schaufelscheiben zur Bestimmung kritischer Schwingungen in Flugtriebwerken}, language = {de} } @inproceedings{BeirowOsterriederKuehhorn, author = {Beirow, Bernd and Osterrieder, Peter and K{\"u}hhorn, Arnold}, title = {Stochastisches Konzept f{\"u}r die Berechnung von Stahlschornsteinen infolge wirbelerregter Querschwingungen}, series = {Berichte der Fachtagung Baustatik - Baupraxis 8, am 21. und 22. M{\"a}rz 2002 in Braunschweig}, booktitle = {Berichte der Fachtagung Baustatik - Baupraxis 8, am 21. und 22. M{\"a}rz 2002 in Braunschweig}, editor = {Dinkler, Dieter}, publisher = {TU, Institut f{\"u}r Statik}, address = {Braunschweig}, isbn = {3-926031-95-6}, pages = {271 -- 280}, language = {de} } @book{KuehhornSilber, author = {K{\"u}hhorn, Arnold and Silber, Gerhard}, title = {Technische Mechanik f{\"u}r Ingenieure}, publisher = {H{\"u}thig-Verlag}, isbn = {3-7785-2620-0}, language = {de} } @inproceedings{StudenerKuehhorn, author = {Studener, Johannes and K{\"u}hhorn, Arnold}, title = {Thermomechanische Simulation des Annealprozesses von großen Siliziumwafern}, series = {Tagungsband, 17. Deutschsprachige ABAQUS-Benutzerkonferenz 2005, 19. - 20. September 2005, N{\"u}rnberg}, booktitle = {Tagungsband, 17. Deutschsprachige ABAQUS-Benutzerkonferenz 2005, 19. - 20. September 2005, N{\"u}rnberg}, publisher = {ABAQUS Deutschland GmbH}, address = {Aachen [u.a.]}, language = {de} } @inproceedings{KlaukeBeirowKuehhorn, author = {Klauke, Thomas and Beirow, Bernd and K{\"u}hhorn, Arnold}, title = {Experimental and numerical investigations of blade mistuning and strain gauge application effects in aero engine development}, language = {en} } @inproceedings{BeirowKuehhornGolzeetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Golze, Mark and Klauke, Thomas}, title = {Strukturdynamische Untersuchungen an Hochdruckverdichterschaufelscheiben unter Ber{\"u}cksichtigung von Mistuningeffekten}, series = {Modalanalyse und Identifikation, Verfahren und Anwendungen bei dynamischen Systemen, Tagung Wiesloch, 25. und 26. Mai 2004}, booktitle = {Modalanalyse und Identifikation, Verfahren und Anwendungen bei dynamischen Systemen, Tagung Wiesloch, 25. und 26. Mai 2004}, publisher = {VDI-Verlag}, address = {D{\"u}sseldorf}, isbn = {3-18-091825-X}, pages = {351 -- 372}, language = {de} } @inproceedings{KlaukeKuehhornBeirow, author = {Klauke, Thomas and K{\"u}hhorn, Arnold and Beirow, Bernd}, title = {Numerische Untersuchung des Schwingverhaltens von Hochdruckverdichter-Blisks mit fertigungsbedingten Anweichungen}, language = {de} } @inproceedings{KlaukeKuehhornLiangetal., author = {Klauke, Thomas and K{\"u}hhorn, Arnold and Liang, Luo and Kober, Markus}, title = {Entwicklung eines 3-Blatt-CFK-Verstellpropellers f{\"u}r Ultraleichtflugzeuge}, abstract = {Internationale AVK-Tagung, 13.-14. September 2010, Essen}, language = {de} } @inproceedings{KlaukeKuehhornLiangetal., author = {Klauke, Thomas and K{\"u}hhorn, Arnold and Liang, Luo and Kober, Markus and Sieghart, D. and F{\"u}hrer, M. and Viehweger, Bernd and Fritzsche, Christoph and Sarradj, Ennes}, title = {Entwicklung eines 3-Blatt-CFK-Verstellpropellers f{\"u}r Ultraleichtflugzeuge}, abstract = {Deutscher Luft- und Raumfahrkongress 2010, 31.08. - 02.09.2010, Hamburg}, language = {de} } @misc{SpringmannKuehhornFilipiaketal., author = {Springmann, Marcel and K{\"u}hhorn, Arnold and Filipiak, A. and Hugler, Daniel and Dufor, K.-H.}, title = {Generisches Flugtriebwerksmodell f{\"u}r die Anwendung in der Vorentwicklungsphase}, language = {de} } @inproceedings{StrehlauKuehhorn, author = {Strehlau, Ulrik and K{\"u}hhorn, Arnold}, title = {Effects of blade mistuning on frequency veering regions of real HPC blisks}, language = {en} } @misc{KoberKuehhorn, author = {Kober, Markus and K{\"u}hhorn, Arnold}, title = {Development of optimized washer-shape for damage-free load application to composites}, series = {Composite Structures}, volume = {92}, journal = {Composite Structures}, number = {9}, issn = {0263-8223}, pages = {1985 -- 1991}, language = {de} } @inproceedings{StrehlauKuehhorn, author = {Strehlau, Ulrik and K{\"u}hhorn, Arnold}, title = {Experimental and numerical investigations of a HPC-Blisk with focus on travelling waves}, language = {en} } @inproceedings{KoberKuehhorn, author = {Kober, Markus and K{\"u}hhorn, Arnold}, title = {Development of optimized washer shape for damage-free load application to composites}, language = {en} } @inproceedings{BeirowKuehhornNipkau, author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Nipkau, Jens}, title = {On the Influence of Strain Gauge Instrumentation on Blade Vibrations of Integral Blisk Compressor Rotors Applying a Discrete Model}, series = {Proceedings of the ASME Turbo Expo 2009, presented at the 2009 ASME Turbo Expo, June 8 - 12, 2009, Orlando, Florida, USA}, booktitle = {Proceedings of the ASME Turbo Expo 2009, presented at the 2009 ASME Turbo Expo, June 8 - 12, 2009, Orlando, Florida, USA}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4887-6}, pages = {245 -- 254}, language = {en} } @inproceedings{KlaukeKuehhornKober, author = {Klauke, Thomas and K{\"u}hhorn, Arnold and Kober, Markus}, title = {Application of a Newer Inter-Fiber-Failure Criteria on CFRPs in Aero Engine Development}, language = {en} } @misc{KuehhornBeirowSchrapeetal., author = {K{\"u}hhorn, Arnold and Beirow, Bernd and Schrape, Sven and Golze, Mark and Kn{\"o}pke, Martin}, title = {Simulation fluidged{\"a}mpfter Strukturschwingungen mittels partitionierter Fluid-Struktur-Kopplung}, series = {Forum der Forschung}, volume = {9}, journal = {Forum der Forschung}, number = {18}, issn = {0947-6989}, pages = {79 -- 86}, language = {de} } @inproceedings{BeirowKuehhornKlauke, author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Klauke, Thomas}, title = {Lokalisierungsph{\"a}nomen bei Hochdruckverdichterschaufelscheiben}, language = {de} } @inproceedings{Kuehhorn, author = {K{\"u}hhorn, Arnold}, title = {Flug-Triebwerkstechnik - innovative Studienrichtung an der BTU Cottbus unter Beteilugung von RRD, MTU und DLR}, series = {Deutscher Luft- und Raumfahrtkongress 2006, Braunschweig, 06. bis 09. November 2006, Bd. 1}, booktitle = {Deutscher Luft- und Raumfahrtkongress 2006, Braunschweig, 06. bis 09. November 2006, Bd. 1}, publisher = {Dt. Ges. f{\"u}r Luft- und Raumfahrt}, address = {Bonn}, pages = {593 -- 596}, language = {de} } @article{KuehhornBeirowKlauke, author = {K{\"u}hhorn, Arnold and Beirow, Bernd and Klauke, Thomas}, title = {Theoretische und experimentelle Untersuchungen von Schaufelschwingungen bei Verdichterintegralr{\"a}dern}, language = {de} } @misc{ZolochevskyGalishinKuehhornetal., author = {Zolochevsky, Alexander and Galishin, A. and K{\"u}hhorn, Arnold and Springmann, Marcel}, title = {Transversal Shear Effect in Moderately Thick Shells from Materials with Characteristics Dependent on the Kind of Stress State under Creep-Damage Conditions: Numerical Modeling}, language = {en} } @misc{ZolochevskyGalishinKuehhornetal., author = {Zolochevsky, Alexander and Galishin, A. and K{\"u}hhorn, Arnold and Springmann, Marcel}, title = {Transversal Shear Effect in Moderately Thick Shells from Materials with Characteristics Dependent on the Kind of Stress State under Creep-Damage Conditions: Theoretical Framework}, language = {en} } @inproceedings{StrehlauKuehhornBeirow, author = {Strehlau, Ulrik and K{\"u}hhorn, Arnold and Beirow, Bernd}, title = {Numerische und experimentelle Untersuchungen realer Hochdruckverdichterschaufelscheiben in Integralbauweise}, language = {de} } @inproceedings{KoberKuehhorn, author = {Kober, Markus and K{\"u}hhorn, Arnold}, title = {Auslegung und Optimierungsprozess einer Tragstruktur in Faserverbundbauweise unter Ber{\"u}cksichtigung moderner Versagenskriterien}, language = {de} } @misc{SpringmannKuehhornKunaetal., author = {Springmann, Marcel and K{\"u}hhorn, Arnold and Kuna, M. and Scherzer, M.}, title = {Influence of Strain Localization on Parameter Identification}, language = {en} } @inproceedings{SpringmannKuehhornFilipiaketal., author = {Springmann, Marcel and K{\"u}hhorn, Arnold and Filipiak, A. and Hugler, Daniel and Dufor, K.-H.}, title = {Automatic generation and optimization of a simplified aircraft engine model using a graphical user interface and full parameterization}, language = {en} } @inproceedings{StrehlauKuehhorn, author = {Strehlau, Ulrik and K{\"u}hhorn, Arnold}, title = {Schwingungsverhalten von Hochdruckverdichterschaufelscheiben in Integralbauweise (Blisk) unter Ber{\"u}cksichtigung h{\"o}herer Schwingungsmoden, Erzeugung und Messung von Umlaufwellen, 3D-Geometrievermessung}, series = {Deutscher Luft- und Raumfahrtkongress 2008, Darmstadt, 23. bis 25. September 2008, Bd. 1}, booktitle = {Deutscher Luft- und Raumfahrtkongress 2008, Darmstadt, 23. bis 25. September 2008, Bd. 1}, publisher = {Dt. Ges. f{\"u}r Luft- und Raumfahrt}, address = {Bonn}, pages = {457 -- 467}, language = {de} } @inproceedings{SchrapeKuehhornNipkauetal., author = {Schrape, S. and K{\"u}hhorn, Arnold and Nipkau, Jens and Beirow, Bernd}, title = {Application of Aeroelastic Methods in Compressor Cascade Configurations Using Partitioned Code Coupling}, language = {en} } @inproceedings{SpringmannKuehhorn, author = {Springmann, Marcel and K{\"u}hhorn, Arnold}, title = {Coupled thermal-multiphase flow analysis in quenching processes for residual stress optimization in compressor and turbine disks}, series = {Proceedings of the ASME Pressure Vessels and Piping Conference - 2008, presented at 2008 ASME Pressure Vessels and Piping Conference, July 27 - 31, 2008, Chicago, Illinois, USA, Vol. 4}, booktitle = {Proceedings of the ASME Pressure Vessels and Piping Conference - 2008, presented at 2008 ASME Pressure Vessels and Piping Conference, July 27 - 31, 2008, Chicago, Illinois, USA, Vol. 4}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4827-2}, pages = {147 -- 156}, language = {en} } @inproceedings{SpringmannSchlumsKuehhorn, author = {Springmann, Marcel and Schlums, H. and K{\"u}hhorn, Arnold}, title = {Numerical simulation of quenching processes for residual stress optimization in compressor and turbine disks}, language = {en} } @inproceedings{BeirowKuehhornSchrape, author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Schrape, S.}, title = {Development of a new Nickel-base Alloy 718Plus for Compressor and Turbine disks}, language = {en} } @inproceedings{KoberKuehhornKlauke, author = {Kober, Markus and K{\"u}hhorn, Arnold and Klauke, Thomas}, title = {Auslegung einer Flanschverbindung aus faserverst{\"a}rktem Kunststoff durch Optimierung der Faserorientierungen und Schichtdicken mit Hilfe von Altair HyperStudy unter Verwendung eines Wirkebenenbruchkriteriums als Nebenbedingung}, language = {de} } @inproceedings{SchrapeKuehhornNipkau, author = {Schrape, S. and K{\"u}hhorn, Arnold and Nipkau, Jens}, title = {Determination of Aerodynamic Damping of Axial-Compressor-Blades Using A Bidirectional Fluid-Structure-Simulation}, series = {1st CEAS European Air and Space Conference 2007, Deutscher Luft- und Raumfahrtkongress 2007, 10 - 13 September 2007, Berlin, Germany, Bd. 1}, booktitle = {1st CEAS European Air and Space Conference 2007, Deutscher Luft- und Raumfahrtkongress 2007, 10 - 13 September 2007, Berlin, Germany, Bd. 1}, publisher = {Dt. Ges. f{\"u}r Luft- und Raumfahrt}, address = {Bonn}, pages = {309 -- 318}, language = {en} } @inproceedings{KlaukeKuehhornBeirow, author = {Klauke, Thomas and K{\"u}hhorn, Arnold and Beirow, Bernd}, title = {Blade Mistuning Induced Blisk Vibration}, series = {1st CEAS European Air and Space Conference 2007, Deutscher Luft- und Raumfahrtkongress 2007, 10 - 13 September 2007, Berlin, Germany, Bd. 1}, booktitle = {1st CEAS European Air and Space Conference 2007, Deutscher Luft- und Raumfahrtkongress 2007, 10 - 13 September 2007, Berlin, Germany, Bd. 1}, publisher = {Dt. Ges. f{\"u}r Luft- und Raumfahrt}, address = {Bonn}, pages = {335 -- 345}, language = {en} } @inproceedings{BeirowKuehhornSchrape, author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Schrape, S.}, title = {Influence of Air Flow on Blisk Vibration Behaviour}, series = {1st CEAS European Air and Space Conference 2007, Deutscher Luft- und Raumfahrtkongress 2007, 10 - 13 September 2007, Berlin, Germany, Bd. 5}, booktitle = {1st CEAS European Air and Space Conference 2007, Deutscher Luft- und Raumfahrtkongress 2007, 10 - 13 September 2007, Berlin, Germany, Bd. 5}, publisher = {Dt. Ges. f{\"u}r Luft- und Raumfahrt}, address = {Bonn}, pages = {3127 -- 3135}, language = {en} } @inproceedings{BeirowKuehhornSchrape, author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Schrape, S.}, title = {Blisk Vibration Phenomena in Consideration of Fluid Structure Interaction}, language = {en} } @inproceedings{KoberKlaukeKuehhornetal., author = {Kober, Markus and Klauke, Thomas and K{\"u}hhorn, Arnold and Lenk, Olaf}, title = {Einbindung eines modernen Wirkebenenbruchkriteriums f{\"u}r faserverst{\"a}rkte Kunststoffe in eine Parameteroptimierung mit Altair HyperStudy}, language = {de} } @inproceedings{KoberKuehhornKlaukeetal., author = {Kober, Markus and K{\"u}hhorn, Arnold and Klauke, Thomas and Lenk, Olaf}, title = {Topology-Optimized Intermediate Casing of Aero Engine and Comparative Evaluation of Titanium and Composite Architecture in Terms of Load Capacity and Weight Reduction}, series = {Proceedings of the ASME Turbo Expo 2008, presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany, Vol. 5, part A}, booktitle = {Proceedings of the ASME Turbo Expo 2008, presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany, Vol. 5, part A}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4315-4}, pages = {69 -- 79}, language = {en} } @inproceedings{BeirowKuehhornSchrape, author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Schrape, S.}, title = {A Discrete model to consider the influence of the air flow on blade vibrations of an intergral blisk compressor rotor}, series = {Proceedings of the ASME Turbo Expo 2008, presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany, Vol. 5, part A}, booktitle = {Proceedings of the ASME Turbo Expo 2008, presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany, Vol. 5, part A}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4315-4}, pages = {381 -- 392}, language = {en} } @inproceedings{KlaukeKuehhornBeirowetal., author = {Klauke, Thomas and K{\"u}hhorn, Arnold and Beirow, Bernd and Parchem, Roland}, title = {Blade Vibration Phenomena of HPC Bliscs Considering Manufacturing Effects and Strain Gauge Application}, series = {Proceedings of the ASME Turbo Expo 2008, presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany, Vol. 5, part A}, booktitle = {Proceedings of the ASME Turbo Expo 2008, presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany, Vol. 5, part A}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4315-4}, pages = {403 -- 413}, language = {en} } @article{NipkauSchrapeBeirowetal., author = {Nipkau, Jens and Schrape, S. and Beirow, Bernd and K{\"u}hhorn, Arnold}, title = {Bestimmung aeroelastischer Parameter einer Hochdruckverdichter Stufe mit Hilfe Fluid-Struktur gekoppelter Berechnungen}, language = {de} } @inproceedings{NipkauKuehhornSchrape, author = {Nipkau, Jens and K{\"u}hhorn, Arnold and Schrape, S.}, title = {Application of Fluid-Structure-Coupling for the Determination of Aeroelastic Parameters of a High-Pressure-Compressor-Blisk-Stage}, language = {en} } @inproceedings{ZuchlinskiKuehhorn, author = {Zuchlinski, Andr{\´e} and K{\"u}hhorn, Arnold}, title = {Strukturelle Optimierung der Aufh{\"a}ngung von heckinstallierten und parametrisierten Turbofantriebwerksmodellen}, language = {de} } @inproceedings{StrehlauKuehhorn, author = {Strehlau, Ulrik and K{\"u}hhorn, Arnold}, title = {Research of higher modes E3E/1 stage 1 demonstrator blisk}, language = {en} } @inproceedings{SchrapeKuehhornNipkau, author = {Schrape, S. and K{\"u}hhorn, Arnold and Nipkau, Jens}, title = {Determination of Aerodynamic Damping of Axial-Compressor-Blades using Fluid-Structure-Interaction Methods}, language = {en} } @inproceedings{HoenischKuehhorn, author = {H{\"o}nisch, Peter and K{\"u}hhorn, Arnold}, title = {Experimentelle und numerische Untersuchungen des Schwingungsverhaltensrealer Radialturbinenlaufr{\"a}der in Integralbauweise (Blisk) im Hinblick auf Verstimmung und Lokalisierung}, language = {de} } @inproceedings{KuehhornStrehlau, author = {K{\"u}hhorn, Arnold and Strehlau, Ulrik}, title = {Verstimmungsuntersuchungen am Laufrad (Blisk) eines modernenFlugtriebwerk-Hochdruckverdichters}, language = {de} } @misc{KoberKuehhorn, author = {Kober, Markus and K{\"u}hhorn, Arnold}, title = {Comparison of different failure criteria for fiber-reinforced plastics in terms of fracture curves for arbitrary stress combinations}, series = {Composites Science and Technology}, volume = {72}, journal = {Composites Science and Technology}, number = {15}, issn = {0266-3538}, doi = {10.1016/j.compscitech.2012.08.007}, pages = {1941 -- 1951}, language = {en} } @inproceedings{GierschBeirowPopigetal., author = {Giersch, Thomas and Beirow, Bernd and Popig, Frederik and K{\"u}hhorn, Arnold}, title = {FSI-based forced response analyses of a mistuned high pressure compressor blisk}, series = {10th International Conference on Vibrations in Rotating Machinery, 11-13 September 2012, IMechE London, UK}, booktitle = {10th International Conference on Vibrations in Rotating Machinery, 11-13 September 2012, IMechE London, UK}, publisher = {Woodhead Publ.}, address = {Cambridge, UK}, isbn = {978-0-85709-452-0}, language = {en} } @inproceedings{RauerKuehhornSpringmann, author = {Rauer, Georg and K{\"u}hhorn, Arnold and Springmann, Marcel}, title = {Residual Stress Simulation of an Aero Engine Disc during Heat Treatment}, series = {Proceedings of the 6th European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2012), Vienna, Austria, September 10-14, 2012}, booktitle = {Proceedings of the 6th European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2012), Vienna, Austria, September 10-14, 2012}, publisher = {Techn. Univ.}, address = {Wien}, isbn = {978-3-9502481-9-7}, language = {en} } @inproceedings{BeirowKuehhornNipkau, author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Nipkau, Jens}, title = {Schwingungsverhalten integraler Hochdruckverdichterlaufr{\"a}der unter Ber{\"u}cksichtigung von Fluid-Struktur-Wechselwirkung und Mistuning}, series = {61. Deutscher Luft- und Raumfahrtkongress 2012, 10. - 12. September 2012, Estrel Berlin}, booktitle = {61. Deutscher Luft- und Raumfahrtkongress 2012, 10. - 12. September 2012, Estrel Berlin}, publisher = {Deutsche Gesellschaft f{\"u}r Luft- und Raumfahrt - Lilienthal-Oberth e.V.}, address = {Bonn}, pages = {9}, language = {de} } @inproceedings{ZuchlinskiKuehhornKoberetal., author = {Zuchlinski, Andr{\´e} and K{\"u}hhorn, Arnold and Kober, Markus and Wehrenpfennig, Lutz}, title = {Kombinierte Topologie- und Parameteroptimierung des Aufh{\"a}ngungssystems von heckinstallierten Turbofantriebwerken}, series = {61. Deutscher Luft- und Raumfahrtkongress 2012, 10. - 12. September 2012, Estrel Berlin}, booktitle = {61. Deutscher Luft- und Raumfahrtkongress 2012, 10. - 12. September 2012, Estrel Berlin}, publisher = {Dt. Ges. f{\"u}r Luft- und Raumfahrt}, address = {Bonn}, pages = {10}, language = {de} } @misc{ZolochevskyParkhomenkoKuehhorn, author = {Zolochevsky, Alexander and Parkhomenko, Larisa and K{\"u}hhorn, Arnold}, title = {Analysis of oxygen exchange-limited transport and chemical stresses in perovskite-type hollow fibers}, series = {Materials Chemistry and Physics}, volume = {135}, journal = {Materials Chemistry and Physics}, number = {2-3}, issn = {0254-0584}, doi = {10.1016/j.matchemphys.2012.05.031}, pages = {594 -- 603}, language = {en} } @inproceedings{GierschHoenischBeirowetal., author = {Giersch, Thomas and H{\"o}nisch, Peter and Beirow, Bernd and K{\"u}hhorn, Arnold}, title = {Forced Response Analyses of Mistuned Radial Inflow Turbines}, series = {Proceedings of the ASME Turbo Expo 2012 : presented at the 2012 ASME Turbo Expo, June 11 - 15, 2012, Copenhagen, Denmark, Vol. 7, part B}, booktitle = {Proceedings of the ASME Turbo Expo 2012 : presented at the 2012 ASME Turbo Expo, June 11 - 15, 2012, Copenhagen, Denmark, Vol. 7, part B}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4473-1}, pages = {1559 -- 1570}, language = {en} } @inproceedings{ReyVillazonKuehhornWeiss, author = {Rey Villaz{\´o}n, Jos{\´e} Maria and K{\"u}hhorn, Arnold and Weiß, Thomas}, title = {A Parametric Impact Study of the Geometry, Air System and Thermal Boundary Conditions on the Life of a Two-Stage High Pressure Turbine}, series = {Proceedings of the ASME Turbo Expo 2012, presented at The ASME 2012 Turbo Expo, June 11-15, 2012, Copenhagen, Denmark, Vol. 7, part A}, booktitle = {Proceedings of the ASME Turbo Expo 2012, presented at The ASME 2012 Turbo Expo, June 11-15, 2012, Copenhagen, Denmark, Vol. 7, part A}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4473-1}, pages = {373 -- 382}, language = {en} } @misc{deSilvaKuehhornGolze, author = {de Silva, Tina and K{\"u}hhorn, Arnold and Golze, Mark}, title = {Homogenization of thin structured sheet metals by using FEM}, series = {Proceedings in applied mathematics and mechanics : PAMM}, volume = {12}, journal = {Proceedings in applied mathematics and mechanics : PAMM}, number = {1}, doi = {10.1002/pamm.201210104}, pages = {227 -- 228}, language = {en} } @misc{ZolochevskyMartynenkoKuehhorn, author = {Zolochevsky, Alexander and Martynenko, Alexander and K{\"u}hhorn, Arnold}, title = {Structural benchmark creep and creep damage testing for finite element analysis with material tension-compression asymmetry and symmetry}, series = {Computers and Structures}, volume = {100-101}, journal = {Computers and Structures}, issn = {0045-7949}, doi = {10.1016/j.compstruc.2012.02.021}, pages = {27 -- 38}, language = {en} } @misc{GierschHoenischBeirowetal., author = {Giersch, Thomas and H{\"o}nisch, Peter and Beirow, Bernd and K{\"u}hhorn, Arnold}, title = {Forced Response Analyses of Mistuned Radial Inflow Turbines}, series = {Journal of Turbomachinery}, volume = {135}, journal = {Journal of Turbomachinery}, number = {3}, issn = {1528-8900}, doi = {10.1115/1.4007512}, pages = {031034-1 -- 031034-9}, abstract = {Radial turbine wheels designed as blade integrated disks (blisk) are widely used in various industrial applications. However, related to the introduction of exhaust gas turbochargers in the field of small and medium sized engines, a sustainable demand for radial turbine wheels has come along. Despite those blisks being state of the art, a number of fundamental problems, mainly referring to fluid-structure-interaction and, therefore, to the vibration behavior, have been reported. Aiming to achieve an enhanced understanding of fluid-structure-interaction in radial turbine wheels, a numerical method, able to predict forced responses of mistuned blisks due to aerodynamic excitation, is presented. In a first step, the unsteady aerodynamic forcing is determined by modeling the spiral casing, the stator vanes, and the rotor blades of the entire turbine stage. In a second step, the aerodynamic damping induced by blade vibration is computed using a harmonic balance technique. The structure itself is represented by a reduced order model being extended by aerodynamic damping effects and aerodynamic forcings. Mistuning is introduced by adjusting the modal stiffness matrix based on results of blade by blade measurements that have been performed at rest. In order to verify the numerical method, the results are compared with strain-gauge data obtained during rig-tests. As a result, a measured low engine order excitation was found by modeling the spiral casing. Furthermore, a localization phenomenon due to frequency mistuning could be proven. The predicted amplitudes are close to the measured data.}, language = {en} } @misc{MahlerdeSilvaKuehhornKober, author = {Mahler-de Silva, Tina and K{\"u}hhorn, Arnold and Kober, Markus}, title = {Developing a Simplified Surrogate Model for Structured Sheet Metals with Numerical and Experimental Comparisons}, series = {Proceedings in applied mathematics and mechanics : PAMM}, volume = {13}, journal = {Proceedings in applied mathematics and mechanics : PAMM}, number = {1}, pages = {99 -- 100}, abstract = {It is important to steadily refine lightweight designs with regard to saving resources and energy in common with good economic efficiency. Thin structured sheet metals offer significantly improved component stiffnesses in addition to an upgraded buckling behavior compared to flat, unstructured sheet metals. By using a distortion energy based homogenization method it is possible to develop a mechanical surrogate model which describes effective mean properties. The accurate selection of symmetric and periodic boundaries enables to determine the required parameters. The conditions are contemplated on elementary cells whose structural mechanical behavior is representative for the elastic behavior of large structures. By doing this, the amount of elements can be reduced and thus the calculating time of large components can considerably be saved. For an efficient surrogate model it is required to analyze and compare numerical with experimental investigations. Some different versions of optimization will be tested to get better approximation of the data.}, language = {en} } @misc{KlaukeStrehlauKuehhorn, author = {Klauke, Thomas and Strehlau, Ulrik and K{\"u}hhorn, Arnold}, title = {Integer Frequency Veering of Mistuned Blade Integrated Disks}, series = {Journal of Turbomachinery}, volume = {135}, journal = {Journal of Turbomachinery}, number = {6}, issn = {1528-8900}, doi = {10.1115/1.4024022}, pages = {061004-1 -- 061004-7}, abstract = {As a result of more balanced blade aspect ratios of modern blade-integrated disks (blisks), interactions between disk-dominated and blade-dominated modes are becoming more and more important, especially if blade mistuning is considered. The specific vibration behavior in these transition regions is characterized by a mix of both fundamental mode types into "coupled" modes. In this paper, numerical and experimental investigations based on a front high-pressure compressor (HPC) blisk stage were carried out in order to determine the effect of blade mistuning on those regions in detail. At this, effects like mode localization and amplitude magnification are found to be weakened in an integer frequency-veering zone. Contrary to this, blisks are very sensitive to mistuning in regions of pure blade-dominated mode families with high modal density.}, language = {en} } @misc{BeirowGierschKuehhornetal., author = {Beirow, Bernd and Giersch, Thomas and K{\"u}hhorn, Arnold and Nipkau, Jens}, title = {Forced Response Analysis of a Mistuned Compressor Blisk}, series = {Journal of Engineering for Gas Turbines and Power}, volume = {136}, journal = {Journal of Engineering for Gas Turbines and Power}, number = {6}, issn = {1528-8919}, doi = {10.1115/1.4026537}, pages = {13}, abstract = {The forced response of an E3E-type high pressure compressor (HPC) blisk front rotor is analyzed with regard to varying mistuning and the consideration of the fluid-structure interaction (FSI). For that purpose, a reduced order model is used in which the disk remains unchanged and mechanical properties of the blades, namely stiffness and damping, are adjusted to measured as well as intentional blade frequency mistuning distributions. The aerodynamic influence coefficient technique is employed to model the aeroelastics. Depending on the blade mode, the exciting engine order, and aerodynamic influences, it is sought for the worst mistuning distributions with respect to the maximum blade displacement based on optimization analyses. Genetic algorithms using blade-alone frequencies as design variables are applied. The validity of the Whitehead limit is assessed in this context. In particular, the question is addressed if and how far aeroelastic effects, mainly caused by aerodynamic damping, combined with mistuning can even cause a reduction of the forced response compared to the ideally tuned blisk. It is shown that the strong dependence of the aerodynamic damping on the interblade phase angle is the main driver for a possible response attenuation considering the fundamental as well as a higher blade mode. Furthermore, the differences to the blisk vibration response without a consideration of the flow and an increase of the disk's stiffness are discussed. Closing, the influence of pure damping mistuning is analyzed again using optimization.}, language = {en} } @misc{BeirowGierschKuehhornetal., author = {Beirow, Bernd and Giersch, Thomas and K{\"u}hhorn, Arnold and Nipkau, Jens}, title = {Optimization-Aided Forced Response Analysis of a Mistuned Compressor Blisk}, series = {Journal of Engineering for Gas Turbines and Power}, volume = {137}, journal = {Journal of Engineering for Gas Turbines and Power}, number = {1}, issn = {1528-8919}, doi = {10.1115/1.4028095}, pages = {012504-1 -- 012504-10}, abstract = {The forced response of the first rotor of an engine 3E (technology program) (E3E)-type high pressure compressor (HPC) blisk is analyzed with regard to varying mistuning, varying engine order (EO) excitations and the consideration of aero-elastic effects. For that purpose, subset of nominal system modes (SNM)-based reduced order models are used in which the disk remains unchanged while the Young's modulus of each blade is used to define experimentally adjusted as well as intentional mistuning patterns. The aerodynamic influence coefficient (AIC) technique is employed to model aero-elastic interactions. Furthermore, based on optimization analyses and depending on the exciting EO and aerodynamic influences it is searched for the worst as well as the best mistuning distributions with respect to the maximum blade displacement. Genetic algorithms using blade stiffness variations as vector of design variables and the maximum blade displacement as objective function are applied. An allowed limit of the blades' Young's modulus standard deviation is formulated as secondary condition. In particular, the question is addressed if and how far the aero-elastic impact, mainly causing aerodynamic damping, combined with mistuning can even yield a reduction of the forced response compared to the ideally tuned blisk. It is shown that the strong dependence of the aerodynamic damping on the interblade phase angle is the main driver for a possible response attenuation considering the fundamental blade mode. The results of the optimization analyses are compared to the forced response due to real, experimentally determined frequency mistuning as well as intentional mistuning.}, language = {en} } @misc{ZolochevskySklepusGalishinetal., author = {Zolochevsky, Alexander and Sklepus, Sergiy and Galishin, Alexander and K{\"u}hhorn, Arnold and Kober, Markus}, title = {A Comparison between the 3D and the Kirchhoff-Love Solutions for Cylinders under Creep-Damage Conditions}, series = {Technische Mechanik}, volume = {34}, journal = {Technische Mechanik}, number = {2}, pages = {104 -- 113}, language = {en} } @inproceedings{KoberKuehhornKaestneretal., author = {Kober, Markus and K{\"u}hhorn, Arnold and K{\"a}stner, Benjamin and Keskin, Akin}, title = {Evaluation of the Stress and Displacement Behavior of Different LS-Dyna Element Types in Combination with Different Anti-Hourglassing Formulations and Initial Element Deformations}, series = {Kurzfassungen der Vortr{\"a}ge, 13. LS-DYNA Forum 2014, 6. - 8. Oktober 2014, Bamberg}, booktitle = {Kurzfassungen der Vortr{\"a}ge, 13. LS-DYNA Forum 2014, 6. - 8. Oktober 2014, Bamberg}, publisher = {DYNAmore GmbH}, address = {Stuttgart}, isbn = {978-3-9816215-1-8}, language = {en} } @inproceedings{KoberKuehhornStelldingeretal., author = {Kober, Markus and K{\"u}hhorn, Arnold and Stelldinger, Enrico and Keskin, Akin}, title = {Identification of Stiffness Parameters of a Simplified Aero-Engine Mount System by Using a Higher Fidelity Model of the Mount System}, series = {Kurzfassungen der Vortr{\"a}ge, 13. LS-DYNA Forum 2014, 6. - 8. Oktober 2014, Bamberg}, booktitle = {Kurzfassungen der Vortr{\"a}ge, 13. LS-DYNA Forum 2014, 6. - 8. Oktober 2014, Bamberg}, publisher = {DYNAmore GmbH}, address = {Stuttgart}, isbn = {978-3-9816215-1-8}, language = {en} } @misc{KoberKuehhornRademannetal., author = {Kober, Markus and K{\"u}hhorn, Arnold and Rademann, J{\"o}rg and M{\"u}ck, Bernhard}, title = {Nonlinear topology optimization of centrifugally loaded aero-engine part with newly developed optimality-criteria based algorithm}, series = {Aerospace Science and Technology}, volume = {Vol. 39}, journal = {Aerospace Science and Technology}, doi = {10.1016/j.ast.2014.09.005}, pages = {705 -- 711}, abstract = {In this paper a successful topology optimization of a centrifugally loaded aero-engine part is presented. For the topology optimization, which is a nonlinear problem due to several contact regions, a self-developed topology optimization algorithm in combination with a commercial FE-solver is used. The goal of the optimization was the reduction of stresses in the structure. ©2014 Rolls-Royce Deutschland Ltd \& Co. KG. Published by Elsevier Masson SAS. All rights reserved.}, language = {en} } @misc{StelldingerKuehhornKober, author = {Stelldinger, Enrico and K{\"u}hhorn, Arnold and Kober, Markus}, title = {Experimental evaluation of the low-velocity impact damage resistance of CFRP tubes with integrated rubber layer}, series = {Composite Structures}, journal = {Composite Structures}, number = {139}, issn = {0263-8223}, doi = {10.1016/j.compstruct.2015.11.069}, pages = {30 -- 35}, abstract = {The impact performance of structural components made of fibre-reinforced plastic is often one of the limiting properties during the design process. To improve the damage resistance regarding transverse low-velocity impact loading, a rubber layer (KRAIBON®) is integrated into the composite laminate of tubular carbon/epoxy specimens. Numerous impact tests, using two different rubber compounds and three different layups, are carried out. The specimens are impacted using a modified Charpy pendulum. Force-time histories have been used to determine the damage threshold load. To visualise damage such as delaminations and inter-fibre failures, the impacted samples have been examined using microsectioning. It is shown that a significant improvement in impact damage resistance can be achieved by integrating a rubber layer into a carbon/epoxy laminate.}, language = {en} } @misc{KoberKuehhornMueck, author = {Kober, Markus and K{\"u}hhorn, Arnold and M{\"u}ck, Bernhard}, title = {Topologieoptimierung eines fliehkraftbelasteten Triebwerkbauteils mit einfach zu implementierendem Algorithmus unter Ber{\"u}cksichtigung mehrerer Zielfunktionen}, series = {NAFEMS-Magazin : Zeitschrift f{\"u}r numerische Simulationsmethoden und angrenzende Gebiete}, journal = {NAFEMS-Magazin : Zeitschrift f{\"u}r numerische Simulationsmethoden und angrenzende Gebiete}, number = {35}, issn = {2311-522x}, pages = {56 -- 66}, language = {de} } @inproceedings{StelldingerGierschFigaschewskyetal., author = {Stelldinger, Marco and Giersch, Thomas and Figaschewsky, Felix and K{\"u}hhorn, Arnold}, title = {A Semi-Unstructured Turbomachinery Meshing Library With Focus on Modeling of Specific Geometrical Features}, series = {ECCOMAS VII European Congress on Computational Methods in Applied Sciences and Engineering, Crete, Greece, June 5-10, 2016}, booktitle = {ECCOMAS VII European Congress on Computational Methods in Applied Sciences and Engineering, Crete, Greece, June 5-10, 2016}, abstract = {Computational Fluid Dynamics is widely used for the analysis and the design of turbomachinery blade rows. A well established method is the application of semi-unstructured meshes, that uses a combination of structured meshes in the radial direction and unstructured meshes in the axial as well as the tangential direction. This takes advantage of the approximately two dimensional flow field through the blade rows, whereby a fine radial discretization, excepting the near wall region, is not necessary. Otherwise, it is possible to discretize particular regions, e.g. the leading and trailing edge regions, in the axial and tangential direction without generating unnecessary nodes in the far field. The meshing approach is based on the projection of a two dimensional unstructured mesh defined at a reference surface. Once, the two dimensional mesh is generated the projection is achieved by transfinite interpolation from the reference surface to further radial surfaces using a structured mesh. Due to the modeling of geometrical features, especially fillets, advanced methods for the generation of structured meshes and mesh smoothing algorithms are required. The paper presents two different approaches for the generation of an appropriate structured mesh. The first is based on the solution of elliptic partial differential equations. The second approach is based on the split of the domain into fourteen appropriately arranged blocks. Furthermore, two smoothing methods for two dimensional unstructured meshes, a constrained Laplace smoothing and an optimization based approach, are presented. Regarding a more realistic representation of the geometry, methods for the modeling of cavities, variable clearance sizes and fillets are presented. Finally, a comparison of the smoothing techniques applied to a rotor passage is presented and the influence of chosen geometrical features on the flow solution is evaluated.}, language = {en} } @inproceedings{MaywaldKuehhornSchrape, author = {Maywald, Thomas and K{\"u}hhorn, Arnold and Schrape, Sven}, title = {Experimental Validation of a Model Update Procedure Focusing on Small Geometric Deviations}, series = {ECCOMAS VII European Congress on Computational Methods in Applied Sciences and Engineering, Crete, Greece, June 5-10, 2016}, booktitle = {ECCOMAS VII European Congress on Computational Methods in Applied Sciences and Engineering, Crete, Greece, June 5-10, 2016}, abstract = {This contribution presents a model update procedure and its experimental validation using the example of a blade integrated disk rotor. This so called blisk is discretized using the finite element method. It is well known that numerical blisk models based on the ideal tuned design show major differences in structural dynamic behavior compared to the real rotor. In this context a modification of the mechanical simulation model should lead to a better accordance of numerical results and the real blisk characteristics. The described model update procedure utilizes data of an optical 3D measurement system. Using this data enables to identify geometric deviations between the ideal design and its real counterpart. Within the update procedure the originally tuned finite element mesh is modified in order to match the measured geometry of the real part. This is done by defining several morph regions. The outer surface nodes of these morph regions change their position along the surface normal vector until they meet the defined deviation constraint. Based on eigenvalue calculations employing free boundary conditions the sensitivity of structural dynamic behavior is shown with respect to small geometric changes. Finally computed eigenvalues and eigenvectors of the updated simulation model are compared with vibration measurement data. A laser Doppler vibrometer is used to detect the vibration responses of the impact excited structure. All experiments are carried out under technical vacuum conditions in order to minimize ambient air damping. In the context of an experimental modal analysis this low damping condition helps to identify more natural frequencies of the investigated structure. This leads to a much more efficient model validation.}, language = {en} } @inproceedings{KoberKuehhornKeskin, author = {Kober, Markus and K{\"u}hhorn, Arnold and Keskin, Akin}, title = {Implicit Time Integration Schemes for the FEM Simulation of Fast Rotating Structures}, series = {WCCM XII \& APCOM VI (World Congress on Computational Mechanics \& Asia Pacific Congress on Computational Mechanics), Seoul, South Korea, 23.-29. Juli 2016}, booktitle = {WCCM XII \& APCOM VI (World Congress on Computational Mechanics \& Asia Pacific Congress on Computational Mechanics), Seoul, South Korea, 23.-29. Juli 2016}, abstract = {Due to the demand of more and more detailed FEM simulation results of whole aero-engine models, the number of DOF of such models (Fig. 1) increases dramatically. Although the available computational power for the solution of such highly nonlinear, dynamic boundary value problems also increased during the last years, the overall computational time of these high-fidelity models for the simulation of a few milliseconds of the running engine is in the order of several weeks even on high performance clusters with thousands of CPU cores. Typically, for such highly dynamic FEM computations explicit time integration schemes are used in order to solve the equations of motion. To keep such a numerical integration stable, the time step size may not exceed a certain critical time step size. Unfortunately, the critical time step size of an explicit time integration algorithm for the engine models under consideration is in the order of 10-8. This means that the simulation of a running engine over a time span of a few seconds results in a computational time of several years with clusters, which are available nowadays. Therefore, implicit time integration schemes, which are unconditionally stable and allow much bigger time steps, have to be used. Since in an implicit integration, in contrast to an explicit one, an equilibrium iteration is always necessary, the computational costs for an implicit time step are much higher than for an explicit time step. Almost all commercial FE codes use the classical Newmark implicit time integration scheme. It will be shown that this algorithm fails especially for the simulation of fast rotating structures if bigger time steps are used. This is demonstrated at the example of academic examples as well as for more realistic rotor models. To overcome the problems of the Newmark integration, a 3-Point-Newmark- Euler-Backward integration scheme [1,2] has been selected, which consists of alternating Newmark and 3-Point-Euler-Backward steps. The additional interpolation information for the Euler-step is provided by the previous Newmark step. This integration procedure has been implemented and successfully applied to the FEM simulation of fast rotating structures, which will be also demonstrated during the presentation.}, language = {en} } @inproceedings{BeirowKuehhornNipkau, author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Nipkau, Jens}, title = {Forced Response Reduction of a Compressor Blisk Rotor Employing Intentional Mistuning}, series = {Advances in Mechanism Design II, Proceedings of the XII International Conference on the Theory of Machines and Mechanisms, 6.-8.9.2016, Liberec}, booktitle = {Advances in Mechanism Design II, Proceedings of the XII International Conference on the Theory of Machines and Mechanisms, 6.-8.9.2016, Liberec}, publisher = {Springer International Publishing}, address = {Cham}, isbn = {978-3-319-44087-3}, doi = {10.1007/978-3-319-44087-3_29}, pages = {223 -- 229}, abstract = {Using the example of a compressor test blisk with 29 blades different sources of mistuning and their consequences for the forced response are analysed under consideration of aeroelastic effects. In particular the impact of superimposing intentional structural mistuning by both random structural mistuning and aerodynamic mistuning is studied. For this purpose reduced order models of the blisk are adjusted for different mistuning distributions. The mistuning itself is characterized by assigning individual stiffness parameters to each blade. The aeroelastic coupling is included employing aerodynamic influence coefficients. By means of genetic algorithm optimizations, structural mistuning patterns are found which yield a mitigation of the forced response below that of the tuned design reference. Ideally a nearly 50 \% reduction of maximum response magnitudes is computed for the fundamental bending mode and large mistuning. The solutions found have been proven to be robust with respect to additional random and aerodynamic mistuning in case of large intentional structural mistuning.}, language = {en} } @inproceedings{WeberKuehhorn, author = {Weber, Robby and K{\"u}hhorn, Arnold}, title = {Reduced Order Analyses of Multi-stage Coupled Structures with Main Focus on Disk-Dominated Modes}, series = {Advances in Mechanism Design II, Proceedings of the XII International Conference on the Theory of Machines and Mechanisms}, booktitle = {Advances in Mechanism Design II, Proceedings of the XII International Conference on the Theory of Machines and Mechanisms}, publisher = {Springer International Publishing}, address = {Cham}, isbn = {978-3-319-44087-3}, doi = {10.1007/978-3-319-44087-3_34}, pages = {263 -- 268}, abstract = {Rotors manufactured as blisk (Blade Integrated Disk) has become state-of-the-art in turbomachinery. This integral design saves a lot of mass and enables higher rotational speeds allowing for higher pressure ratios and hence an increased efficiency. The advantage comes along with the drawback that the structural damping level is extremely low. Nowadays, the dynamics of single-stage rotors is well-investigated, as dynamical analysis of cyclic structures is one of the most important subjects in applied research in turbomachinery. However, the stage-to-stage coupling effect is neglected in most cases. The importance of proper interstage treatment is obvious for adequate multi-stage analyses. Hence the structural dynamics of a multi-stage assembly has recently become an important area of research. In this paper, some multi-stage effects are discussed and three different reduced order techniques are summarized and demonstrated on a multi-stage assembly of academic blisks. The findings are compared to a FE-solution. Particular attention must be paid to disk-dominated modes, which are highly affected by multi-stage behavior. Mistuning modeling is not considered, because it mainly influences blade-dominated vibrations.}, language = {en} } @inproceedings{WeberKuehhorn, author = {Weber, Robby and K{\"u}hhorn, Arnold}, title = {Uncertainty Quantification for Predicted Endurance due to Mistuning in Turbomachinery}, series = {Proceedings of International Conference on Uncertainty in Structural Dynamics (USD 2016), 19 to 21 September, 2016, Leuven, Belgium}, booktitle = {Proceedings of International Conference on Uncertainty in Structural Dynamics (USD 2016), 19 to 21 September, 2016, Leuven, Belgium}, publisher = {Departement Werktuigkunde}, address = {Heverlee (Belgium)}, isbn = {978-90-73802-94-0}, abstract = {Rotors manufactured as blisk (Blade Integrated Disk) are manifoldly used in state-of-the-art turbomachinery. Commonly, the endurance is evaluated by a numerical analysis of as designed rotor. Since small deviations due to the manufacturing cause slightly different blades, mistuning in turbomachinery is unavoidable. Mistuning causes increased vibration amplitudes - higher than those to be expected in case of the ideal design intention. Nowadays, there are various model updating procedures to ensure a more realistic modelling of blisks. Within Monte Carlo simulations, one obtains a well-approximated maximum vibration amplitude at tolerable costs, the effect of fractional alterations of eigenmodes due to geometric imperfections is normally neglected. Value and location of maximum stress are sensitive to geometric deviations but also decisive for an adequate calculation of the High Cycle Fatigue, which itself is one of the main causes of blisk failure.}, language = {en} } @misc{BeirowFigaschewskyKuehhornetal., author = {Beirow, Bernd and Figaschewsky, Felix and K{\"u}hhorn, Arnold and Bornholm, Alfons}, title = {Modal Analyses of an Axial Turbine Blisk With Intentional Mistuning}, series = {Journal of Engineering for Gas Turbines and Power}, volume = {140}, journal = {Journal of Engineering for Gas Turbines and Power}, number = {1}, issn = {0742-4795}, doi = {10.1115/1.4037588}, pages = {012503-1 -- 012503-11}, abstract = {The potential of intentional mistuning to reduce the maximum forced response is analyzed within the development of an axial turbine blisk for ship diesel engine turbocharger applications. The basic idea of the approach is to provide an increased aerodynamic damping level for particular engine order excitations and mode shapes without any significant distortions of the aerodynamic performance. The mistuning pattern intended to yield a mitigation of the forced response is derived from an optimization study applying genetic algorithms. Two blisk prototypes have been manufactured a first one with and another one without employing intentional mistuning. Hence, the differences regarding the real mistuning and other modal properties can be experimentally determined and evaluated as well. In addition, the experimental data basis allows for updating structural models which are well suited to compute the forced response under operational conditions. In this way, the real benefit achieved with the application of intentional mistuning is demonstrated.}, language = {en} } @misc{KoberKuehhorn, author = {Kober, Markus and K{\"u}hhorn, Arnold}, title = {Stable implicit time-integration of flexible rotating structures—explanation for instabilities and concepts for avoidance}, series = {Applied Mathematical Modelling}, volume = {60}, journal = {Applied Mathematical Modelling}, issn = {0307-904X}, doi = {10.1016/j.apm.2018.03.017}, pages = {235 -- 243}, abstract = {Instabilities occurring during the implicit time-integration are still handicapping a time-efficient solution of large FEM systems of equations. Especially the simulation of flexible rotating structures is barely mastered by implicit FEM codes. For this, the Newmark algorithm and related algorithms are used for many years. Here, we derive the reasons for the mentioned inevitable numerical issues and present concepts that lead to an efficient and stable solution.}, language = {en} } @misc{BeirowKuehhornFigaschewskyetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Figaschewsky, Felix and Bornholm, Alfons and Repetckii, Oleg V.}, title = {Forced Response Reduction of a Blisk by Means of Intentional Mistuning}, series = {Journal of Engineering for Gas Turbines and Power}, volume = {141}, journal = {Journal of Engineering for Gas Turbines and Power}, number = {1}, issn = {1528-8919}, doi = {10.1115/1.4040715}, pages = {011008-1 -- 011008-8}, abstract = {The effect of intentional mistuning has been analyzed for an axial turbocharger blisk with the objective of limiting the forced response due to low engine order excitation (LEO). The idea behind the approach was to increase the aerodynamic damping for the most critical fundamental mode in a way that a safe operation is ensured without severely losing aerodynamic performance. Apart from alternate mistuning a more effective mistuning pattern is investigated, which has been derived by means of optimization employing genetic algorithms. In order to keep the manufacturing effort as small as possible only two blade different geometries have been allowed which means that an integer optimization problem has been formulated. Two blisk prototypes have been manufactured for the purpose of demonstrating the benefit of the intentional mistuning pattern identified in this way: A first one with and a second one without employing intentional mistuning. The real mistuning of the prototypes has been experimentally identified. It is shown that the benefit regarding the forced response reduction is retained in spite of the negative impact of unavoidable additional mistuning due to the manufacturing process. Independently, further analyzes have been focused on the robustness of the solution by considering increasing random structural mistuning and aerodynamic mistuning as well. The latter one has been modeled by means of varying aerodynamic influence coefficients (AIC) as part of Monte Carlo simulations. Reduced order models have been employed for these purposes.}, language = {en} } @misc{WeberKuehhornHeinrich, author = {Weber, Robby and K{\"u}hhorn, Arnold and Heinrich, Christoph Rocky}, title = {Modelling and analysis of a high-speed turbine impeller concerning mistuning}, series = {The 14th International Conference of machinery (VETOMAC XIV), Lissabon, 10-13 September 2018}, journal = {The 14th International Conference of machinery (VETOMAC XIV), Lissabon, 10-13 September 2018}, doi = {10.1051/matecconf/201821118002}, pages = {6}, abstract = {As-manufactured impellers behave significantly different from nominal impellers. There are no identical blades due to geometric and material deviations. In this paper three model updating procedures are discussed with the objective to achieve realistic models of as-manufactured impellers. The techniques are applied to radial inflow turbine wheel of an exhaust gas turbocharger. The first approach creates a model through optical measurement and mesh morphing. The second approach is based on a contactless measurement of blade individual vibration responses. An iterative update process gains the corresponding mistuning pattern and thus the associated model. Third, a model is found by an optimisation, that identified a mistuning pattern, that fits modal characteristics, which are evaluated during experimental modal analysis at vacuum. In-depth analyses of these models are realised to determine advantages and drawbacks of the procedures.}, language = {en} } @misc{WeberKuehhorn, author = {Weber, Robby and K{\"u}hhorn, Arnold}, title = {Mistuning Identification Approach With Focus on High-Speed Centrifugal Compressors}, series = {ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, Volume 7C: Structures and Dynamics, Oslo, Norway, June 11-15, 2018}, journal = {ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, Volume 7C: Structures and Dynamics, Oslo, Norway, June 11-15, 2018}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5115-9}, doi = {10.1115/GT2018-75382}, pages = {10}, abstract = {Blade vibrations are one of the main cost drivers in turbo-machinery. Computational blade vibration analysis facilitates an enormous potential to increase the productivity in the design of bladed components. Increasing computing power as well as improved modeling and simulation methods lead to comprehensive calculation results. This allows for a more precise prediction and assessment of experimental data. Usually, in the field of turbomachinery, identical blades are assumed to lower the required computational resources. However, mistuning is unavoidable, since small deviations due to the manufacturing process will lead to slightly different blade behavior. Potential effects such as mode localization and amplification can be treated statistically and have been thoroughly studied in the past. Since then, several reduced order models (ROMs) have been invented in order to calculate the maximum vibration amplitude of a fleet of mistuned blisks. Most commonly, mistuning is thereby modeled by small material deviations from blade to blade, e.g. Young's modulus or density. Nowadays, it is common knowledge that the level of manufacturing imperfection (referred as level of mistuning) significantly influence mode localization as well as vibration amplification effects. Optical measurements of the geometric deviations of manufactured blades and converting to a high-fidelity finite element model make huge progress. However, to the knowledge of the authors, there is no reliable method, that derives a characteristic quantity from the geometric mistuning, that fits into the mentioned statistically approaches. Therefore, experimental data is needed to quantify the level of mistuning. Several approaches, which isolate blade individual parameters, are used to identify the dynamic behavior of axial compressors and turbines. These methods can be applied to medium-speed centrifugal turbine wheels but tend to fail to evaluate high-speed compressor with splitter blades. This paper briefly presents the original approach and discusses the reasons for failure. Thereafter, a new approach is proposed. Finally the level of mistuning and important quantities to perform a statistical evaluation of a high-speed compressor is shown. Copyright © 2018 by ASME}, language = {en} } @misc{WagnerKuehhornJanetzkeetal., author = {Wagner, Frank and K{\"u}hhorn, Arnold and Janetzke, Timm and Gerstberger, Ulf}, title = {Multi-Objective Optimization of the Cooling Configuration of a High Pressure Turbine Blade}, series = {ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, Volume 5C: Heat Transfer Oslo, Norway, June 11-15, 2018}, journal = {ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, Volume 5C: Heat Transfer Oslo, Norway, June 11-15, 2018}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5110-4}, doi = {10.1115/GT2018-75616}, pages = {10}, abstract = {Due to the increasing turbine inlet temperature and in order to improve the overall efficiency it is necessary to optimize the cooling design of the hot gas components of an aero engine. The current paper discusses the strategy of optimizing a rotor blade cooling configuration of a small civil aero engine, comprising of films and internal turbulators (ribs). An insight into the parametrization is given including the location of the films and ribs as well as the number of the films and ribs. The parameter reduction results in 18 input parameters for the optimizations to limit the number of parameters to an acceptable level. Two optimizations are carried out with the primary objectives of non-dimensional mass flow and overall cooling effectiveness. Different optimization algorithms are used, namely AMGA and NSGA-II, and compared afterwards. A further optimization is carried out with direct objectives of mass flow and mean surface temperature using the AMGA algorithm. The outputs from the optimizations are presented as a pareto-front. These plots are used for a comparison of the optimization algorithms and formulations respectively. Finally, the differences are discussed and the advantages and disadvantages of the algorithms used are highlighted. Copyright © 2018 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @misc{BeirowFigaschewskyKuehhornetal., author = {Beirow, Bernd and Figaschewsky, Felix and K{\"u}hhorn, Arnold and Bornholm, Alfons}, title = {Vibration Analysis of an Axial Turbine Blisk with Optimized Intentional Mistuning Pattern}, series = {Journal of Sound and Vibration}, volume = {442}, journal = {Journal of Sound and Vibration}, issn = {0022-460X}, doi = {10.1016/j.jsv.2018.10.064}, pages = {11 -- 27}, abstract = {With the objective of attenuating the forced response of an axial turbine blisk for ship Diesel engine applications efforts have been made to increase the aerodynamic damping contribution for the most critical modes. In this regard the potential of intentional mistuning is investigated since it offers the opportunity to ensure a safe operation without a severe loss of aerodynamic performance. Genetic algorithms have been chosen to derive an optimized mistuning pattern resulting in a forced response clearly below that of the tuned counterpart. In order to keep the manufacturing effort within a limit only two possible blade geometries are allowed, which means that an integer optimization problem has been formulated. For the purpose of demonstrating the benefit of the intentional mistuning pattern found, two blisk prototypes have been manufactured: One with and another one without employing intentional mistuning for purposes of comparison. Furthermore, this offers the opportunity for an experimental determination of actually manufactured mistuning and other modal properties as well. The experimental data basis is employed to update structural models, which are well suited to demonstrate the forced response reduction under operational conditions. Finally, the robustness of the gain achieved with intentional mistuning could be proved towards both additional but unavoidable random structural and aerodynamic mistuning.}, language = {en} } @misc{FigaschewskyHanschkeKuehhorn, author = {Figaschewsky, Felix and Hanschke, Benjamin and K{\"u}hhorn, Arnold}, title = {Efficient Generation of Engine Representative Tip Timing Data Based on a Reduced Order Model for Bladed Rotors}, series = {Journal of Engineering for Gas Turbines and Power}, volume = {141}, journal = {Journal of Engineering for Gas Turbines and Power}, number = {1}, issn = {0742-4795}, doi = {10.1115/1.4040748}, pages = {9}, language = {en} } @misc{FigaschewskyHanschkeKuehhorn, author = {Figaschewsky, Felix and Hanschke, Benjamin and K{\"u}hhorn, Arnold}, title = {Efficient Generation of Engine Representative Tip Timing Data Based on a Reduced Order Model for Bladed Rotors}, series = {ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, Volume 7C: Structures and Dynamics, Oslo, Norway, June 11-15, 2018}, journal = {ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, Volume 7C: Structures and Dynamics, Oslo, Norway, June 11-15, 2018}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5115-9}, doi = {10.1115/GT2018-76342}, pages = {12}, abstract = {In modern compressors the assessment of blade vibration levels as well as health monitoring of the components are fundamental tasks. Traditionally, this assessment is done by the application of strain gauges to some blades of the assembly. In contrast to strain gauges, blade tip timing (BTT) offers a contactless monitoring of all blades of a rotor and there is no need of a telemetry system. A major issue in the interpretation of BTT data is the heavily undersampled nature of the signal. Usually, newly developed BTT algorithms are tested with sample data created by simplified structural models neglecting many of the uncertainties and disturbing influences of real applications. This work focuses on the creation of simulated BTT datasets as close as possible to real case measurements. For this purpose a subset of nominal system modes (SNM) representation of a compressor rotor is utilized. This model is able to include a large number of features present in real measurements, such as mistuning, static blade deflections due to centrifugal loads, aerodynamic damping and multiple mode resonances. Additionally, manufacturing deviations of the blade geometry, probe positioning errors in the BTT system and noise in the time of arrivals (TOAs) are captured by the BTT simulation environment. The main advantage of the created data is the possibility to steadily increase the signal complexity. Starting with a "perfect" signal the simulation environment is able to add different uncertainties one after the other. This allows the assessment of the influence of different features occurring in real measurements on the performance and accuracy of the analysis algorithms. Finally, a comparison of simulated BTT data and real data acquired from a rig test is shown to validate the presented approach of BTT data generation. Copyright © 2018 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @misc{WeberKuehhorn, author = {Weber, Robby and K{\"u}hhorn, Arnold}, title = {Mistuning Identification Approach With Focus on High-Speed Centrifugal Compressors}, series = {Journal of Engineering for Gas Turbines and Power}, volume = {14}, journal = {Journal of Engineering for Gas Turbines and Power}, number = {3}, issn = {1528-8919}, doi = {10.1115/1.4040999}, pages = {7}, language = {en} } @misc{WeberKuehhornBeirow, author = {Weber, Robby and K{\"u}hhorn, Arnold and Beirow, Bernd}, title = {Mistuning und D{\"a}mpfung radialer Turbinen- und Verdichterlaufr{\"a}der}, series = {MTZ - Motortechnische Zeitschrift}, volume = {80}, journal = {MTZ - Motortechnische Zeitschrift}, number = {9}, issn = {0024-8525}, doi = {10.1007/s35146-019-0094-2}, pages = {74 -- 78}, abstract = {Turbolader tragen erheblich zur Steigerung des Motorenwirkungsgrads bei. Rotierende Komponenten sind infolge der Fliehkraft, der zur Aufladung notwendigen Str{\"o}mungsumlenkungen, der instation{\"a}ren Druckschwankungen der Str{\"o}mung sowie von Temperaturgradienten als hochbelastete Laufr{\"a}der einzustufen, die unter erheblicher Schwingungsanf{\"a}lligkeit leiden. Am Lehrstuhl Strukturmechanik und Fahrzeugschwingungen der BTU Cottbus-Senftenberg wurde im Rahmen eines FVV-Forschungsvorhabens der Einfluss der fertigungsbedingten Toleranzen auf eben jenes Schwingungsverhalten untersucht. Es wird nachgewiesen, dass Intentional Mistuning zu signifikant niedrigeren Belastungen f{\"u}hren kann.}, language = {de} } @misc{FranzKuehhornGierschetal., author = {Franz, Falco and K{\"u}hhorn, Arnold and Giersch, Thomas and Schrape, Sven and Figaschewsky, Felix}, title = {Influence of Inlet Distortions on the Forced Vibration of a High Pressure Compressor Rig}, series = {ASME 2020 Turbo Expo - Virtual Conference, September 2020}, journal = {ASME 2020 Turbo Expo - Virtual Conference, September 2020}, abstract = {The accurate prediction of blade vibrations is a key factor for the development of reliable turbomachines. This paper focusses on forced vibrations. The excitation frequency is an integer multiple of the rotor revolution frequency, which is commonly called engine order. Aerodynamic excitation of blades is created by stator wakes or the potential fields of downstream obstacles, which usually leads to high engine orders correlating to the number of vanes. Resonance crossings appear at higher frequencies corresponding to higher modes. Besides high engine orders, low engine orders not related to the number of vanes may exist. They can be caused by a disturbance of the perfect cyclic symmetry of the flow pattern due to geometry variations or inlet distortions. Inlet distortions result from installation effects, maneuvers or crosswind. Low engine orders affect fundamental modes at high engine speeds. High static loads due to centrifugal forces combined with dynamic excitation and low damping may lead to unacceptable high stresses. This paper aims at getting a better understanding of the simulative prediction of low engine order excitation with special focus on inlet distortions. Under investigation is a 4.5 stage research compressor rig, for which an extensive amount of test data is available. A three dimensional CFD-model of the compressor is used to compute the forcings generated by different distortion patterns. The first two stages are modeled as a full-annulus, which allows to fully resolve the spatial content of the inlet distortion patterns. The rotor 2 blisk is of special interest in this investigation. The propagation of the distortion after stage 2 with rotor 2 is not of interest, therefore the downstream stages are modeled as single passages in order to save computational time. The distortion patterns are the outcome of traversals of different screens with total pressure probes. During distortion measurements, the screens located in the inlet duct were rotated relative to the fixed instrumentation. The traversals in resonance of the first bending mode of rotor 2 with a low engine order four showed a dependency of the screen angle on the vibration amplitude. Acceleration and deceleration maneuvers through this resonance were conducted with screen angles set to those of smallest and highest response. Vibration amplitudes of the blisk rotor are measured by strain gauges and a blade tip timing system. Simulation results are compared against vibration measurements. Aerodynamic damping is calculated with the influence coefficient method. The effects of mistuning are included in the calculation of vibration amplitudes via a subset of nominal system modes model to give a meaningful comparison against real engine hardware. The mistuning distribution of the blisk was identified at rest for the fundamental bending mode. The presence of a 2nd excitation mechanism of unknown source explains the observed test data. This unknown source is not included in the CFD model. A direct comparison of simulation and measurement is still possible by leveraging the observed superposition effects of both excitation sources. The consequent approach is to identify and substract the forcing due to the unknown source, leaving only the delta forcing due to inlet distortions.}, language = {en} } @misc{GambittaKuehhornSchrape, author = {Gambitta, Marco and K{\"u}hhorn, Arnold and Schrape, Sven}, title = {Geometrical Variability Modelling of Axial Compressor Blisk Aerofoils and Evaluation of Impact on the Forced Response Problem}, series = {ASME 2020 Turbo Expo - Virtual Conference, September 2020}, journal = {ASME 2020 Turbo Expo - Virtual Conference, September 2020}, abstract = {The manufacturing process always produces onto the components a certain amount of geometrical uncertainty. This results inevitably in the introduction of a certain amount of variability within the manufactured parts. Even if the differences are small, all the resulting geometries will differ from each other. The present work focuses on the effect of the manufacturing geometrical variability on the high pressure compressor of a turbofan engine for civil aviation. The deviations of the geometry over the axial compressor blades are studied and modelled for the representation in the computational models. Such variability is of particular interest for the forced response problem, where small deviations of the geometry from the ideal nominal model can imply significant differences in the vibrational responses. The information regarding the geometrical mistuning is extracted from a set of manufactured components surface scans of a blade integrated disk (blisk) rotor. The measured geometries are analyzed over a large amount of set radial sections, defining a set of opportune parameters to represent the deviations from the nominal design. A spline fit of the parameters over the radial sections allows the creation of a set of variables describing the geometry. The dimension of the variables domain is reduced using the principal component analysis approach, this allows to obtain an optimal subset of geometrical modes as linear combination of the above mentioned parameters. The reconstruction of the modelled geometries is performed for the implementation in complex CFD and FEM solvers. This is done via the application of the modelled delta nominal-to-measure geometrical offset to the hot geometry of the desired test case. The generated model allows a stochastic representation of the variability, providing an optimal set of variables to represent it. Moreover the approach as defined allows to apply the modelled variability to different blades, e.g. different stators or rotors, utilizing the nominal geometry as input. The aeroelastic analyses considering geometry based mistuning is carried on a test-rig case, focusing on how such variability can affect the modal forcing generated on the blades. A validated CFD model is used to extract the force generated by the unsteady pressure field over the selected vibrational mode shapes of the rotor blades. The blade mode shapes are extracted form a FEM model of the whole blisk and the blades displacements are mapped over the CFD model nodes. The uncertainty quantification of the geometrical variability effect on the modal forcing is performed utilizing Monte Carlo methods. A reduced model for the CFD solution is employed, utilizing a single passage multi blade row which assumes a time-space periodicity solving the governing equations in the frequency domain. This allows for conducting an uncertainty quantification considering the large domain of the variables used to describe the geometries compared to the computational resources needed for the single solution. The unsteady modal forcing is studied as amplitude and phase shift for the different engine orders (frequencies arising from the engine working condition as higher harmonics of the shaft speed). In particular the scatter of the main engine orders forcing amplitudes for the manufactured blades can be compared with the nominal responses to predict the possible amplification due to the geometrical variability. Finally the results are compared to a larger computational model to assess the influence of multiple variable blades in the assembly.}, language = {en} } @misc{HeinrichKuehhornSteffetal., author = {Heinrich, Christoph Rocky and K{\"u}hhorn, Arnold and Steff, Klaus and Petry, Nico}, title = {Generalized Model for the Approximation of Coupled Acousto-Mechanical Natural Frequencies in High-Pressure Centrifugal Compressors}, series = {ASME 2020 Turbo Expo - Virtual Conference, Spetember 2020}, journal = {ASME 2020 Turbo Expo - Virtual Conference, Spetember 2020}, abstract = {The oil and gas, chemical, and process industries employ centrifugal compressors for a wide range of applications. Due to this, the conditions, under which centrifugal compressors have to operate, vary significantly from case to case. Gas pipeline compressors, for example, may feature discharge pressures well over 100 bar (1450 psi). In other fields of application, like gas injection, which is used to enhance oil recovery, this quantity can reach considerably higher values. Here, discharge pressures over 600 bar (8702 psi) and gas densities over 300 kg/m3 (18.7284 lb/ft3) are not uncommon. During the last decades, comprehensive research was conducted on the impact of high pressure operating conditions on the vibrational behavior of centrifugal compressor wheels. Nowadays, it is well-known that an increase in gas pressure levels leads to a more pronounced interaction between the side cavities and the impeller, which results in a frequency shift of the acoustic and structural modes. For the safe operation of compressors, it is necessary to predict these coupled natural frequencies accurately. The state-of-the-art approach to achieve this objective is the finite element method. While this technique provides high-quality results, the simulation of acousto-mechanical systems is still a time-consuming process that incurs high computational costs. Therefore, finite element models are, in this case, not suitable for probabilistic studies, sensitivity analyses, and comprehensive simulations of the full operating range of the compressor. In 2013, Magara proposed a simplified model based on an annular plate between two cylindrical cavities to solve this problem. While this method reduces the required computational effort significantly, its use is limited to platelike impellers. The authors of the current paper propose a more generalized method to overcome the challenges mentioned above. It uses the uncoupled structural and acoustic modes of the actual impeller and side cavities in a modal superposition to approximate the natural frequencies of the coupled acousto-mechanical system. In this way, the intended design geometries of the impeller and side cavities are considered while maintaining the advantages of Magara's model regarding the computational effort. In a numerical study, Magara's method and the generalized model are applied to different systems of increasing complexity. The investigation starts with a simple annular plate in a cylindrical cavity and ends with two actual compressor impellers. At every complexity level, the results of both approaches are compared to a finite element analysis. Moreover, measurement data of a simplified rotor in a cylindrical cavity is used to validate the numerical models. Finally, the paper concludes with a discussion of the limitations and benefits of all employed numerical methods.}, language = {en} } @misc{ElMasryKuehhornFigaschewsky, author = {ElMasry, Seif and K{\"u}hhorn, Arnold and Figaschewsky, Felix}, title = {Investigation of Working Line Variation Onto Forced Response Vibrations of a Compressor Blisk}, series = {Turbo Expo 2021, Virtual Conference and Exhibition: September 21, 2020}, journal = {Turbo Expo 2021, Virtual Conference and Exhibition: September 21, 2020}, abstract = {Avoidance of high vibration amplitudes of rotor blades on the conventional working line of the compressor is a design requirement. However, rotors of aircraft engine compressors could temporarily operate near choke and stall conditions, due to transient manoeuvers or deterioration. As a result, the vibration levels might change, which could lead to a premature high cycle fatigue of the blades. This paper aims at studying the effect of different throttle positions at five constant aerodynamic speed lines ranging from 60\% to 100\% of the maximum speed onto the resulting vibration amplitudes and aerodynamic damping values on an integrally bladed disk (blisk) of a transonic research compressor. Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) simulations are performed via an automated workflow, which reads aerodynamic data of the operating points of interest and runs all necessary aeromechanic computations along with their corresponding post-processing routines to calculate the resulting system response and amplitude frequency values. Using this workflow, Eigenfrequencies and mode-shapes of the rotor blades are obtained through multiple FEA simulations that are automatically executed at all relevant shaft speeds. The time-averaged flow pressure field on the blades is extracted from steady CFD simulations of the whole compressor and mapped onto the structural mesh of the rotor. Through a Spokes diagram, operating points in close proximity to resonance spots are identified, as well as their corresponding excited vibration modes. To obtain the time-variable flow pressure fields on the blades, unsteady CFD simulations are performed using a single passage model of the rotor with its upstream and downstream stators, as space-time periodicity of the flow data across the annulus is assumed. Additionally, a CFD rotor model with only a quarter section of the full annulus is built, where a unidirectional coupling approach between the structure and the fluid is applied to calculate the aerodynamic damping values. The calculated vibration amplitudes at engine orders of interest are then compared to strain gauge readings of a corresponding rig test. After validation of the simulation data, the sensitivity of the forced response due to working line variations is studied. Looking at the maximum aerodynamic speed line, it is clear that operating points near compressor stall are accompanied by high vibration response relative to the aerodynamic design point. A possible reason for this amplification is the change of flow incidence and the increase of pressure loss at the upstream blade-row. However, this effect becomes less articulated in the lower speed lines, where amplitudes of the forced vibrations change only slightly between different throttling positions. In this paper, the three-dimensional flow inside the passages is also carefully studied, which allows to better understand the relationship between flow characteristics and the resulting vibration response of compressor blades.}, language = {en} } @misc{HardenbergKuehhornFanter, author = {Hardenberg, Alexander and K{\"u}hhorn, Arnold and Fanter, Maren}, title = {Correlating and Updating Finite Element Models of Different Fidelity Using an Energy-Based Approach}, series = {Turbo Expo 2020, Virtual Conference, Virtual Conference and Exhibition, Online, September 21 - 25, 2020}, journal = {Turbo Expo 2020, Virtual Conference, Virtual Conference and Exhibition, Online, September 21 - 25, 2020}, abstract = {Building finite element models of complex structures requires the engineer to make various simplifying assumptions. While there exists no unique way of modeling, the resulting model depends to a level on experience and engineering judgement. The inherent model uncertainties can be subdivided into three categories: idealization errors, discretization errors and parameter errors. Understanding the effect of different modeling assumptions and minimizing these uncertainties is key for creating efficient and physical meaningful finite element models. In this paper the effects of different modeling assumptions are analyzed by comparing finite element models of an aero engine turbine casing. Various models of different fidelity are created reaching from simple shell element representations neglecting geometric features like bosses, fixings and holes, to higher fidelity mixed dimensional models using coupled shell and three-dimensional elements. To quantify their impact on the stiffness and mass properties, the different models are correlated with a high-fidelity three-dimensional finite element model using numerical modal data. A novel method is proposed based on the strain and kinetic energy distribution to assess the effect of different modeling assumptions on the model structure. This is done by splitting the discretized model into multiple sections of interest and calculating the perturbation of energies within the related splits. The derived strain and kinetic energy perturbations are then used in addition to other correlation criteria like the modal assurance criteria or the relative difference in eigenfrequencies to analyze the impact of the different modeling assumptions. Having quantified the differences, the difficulties of error localization using modal data are discussed in the context of the correlation results. Finally, the effectiveness of the derived perturbation values are demonstrated by updating a finite element model of an aero engine turbine casing in the presence of structural simplifications using an evolutionary optimization algorithm and comparing the model updating strategy to the standard sensitivity-based updating approach. If the resulting updated model is used to predict structural modifications or untested loading conditions, the updated parameters might lose their physical meaning when altering regions of the model not in error. Therefore, it is important to examine the physical significance of the updated parameters. It is shown how the energy-based approach can help to address this problem. All in all, the proposed energy-based approach can be used to compare various modeling strategies in order to build efficient finite element models as well as assist in the choice of parameters for subsequent model updating to validate the numerical model against test data.}, language = {en} } @misc{NoackKuehhornKoberetal., author = {Noack, Martin and K{\"u}hhorn, Arnold and Kober, Markus and Firl, Matthias}, title = {A new stress-based topology optimization approach for finding flexible structures}, series = {Structural and Multidisciplinary Optimization}, volume = {64}, journal = {Structural and Multidisciplinary Optimization}, number = {4}, issn = {1615-147X}, doi = {10.1007/s00158-021-02960-w}, pages = {1997 -- 2007}, abstract = {This paper presents a new FE-based stress-related topology optimization approach for finding bending governed flexible designs. Thereby, the knowledge about an output displacement or force as well as the detailed mounting position is not necessary for the application. The newly developed objective function makes use of the varying stress distribution in the cross section of flexible structures. Hence, each element of the design space must be evaluated with respect to its stress state. Therefore, the method prefers elements experiencing a bending or shear load over elements which are mainly subjected to membrane stresses. In order to determine the stress state of the elements, we use the principal stresses at the Gauss points. For demonstrating the feasibility of the new topology optimization approach, three academic examples are presented and discussed. As a result, the developed sensitivity-based algorithm is able to find usable flexible design concepts with a nearly discrete 0 - 1 density distribution for these examples.}, language = {en} } @inproceedings{BeirowFigaschewskyKuehhorn, author = {Beirow, Bernd and Figaschewsky, Felix and K{\"u}hhorn, Arnold}, title = {An Inverse Approach to Identify Tuned Aerodynamic Damping, System Frequencies, and Mistuning, Part 2: Application to Blisks at Rest}, series = {Proceedings of the 15th International Symposium on Unsteady Aerodynamics, Aeroacoustics \& Aeroelasticity of Turbomachines, ISUAAAT15, 24-27 September 2018, University of Oxford, UK}, booktitle = {Proceedings of the 15th International Symposium on Unsteady Aerodynamics, Aeroacoustics \& Aeroelasticity of Turbomachines, ISUAAAT15, 24-27 September 2018, University of Oxford, UK}, publisher = {ISUAAAT Scientific Committee}, pages = {2}, language = {en} } @inproceedings{FigaschewskyKuehhorn, author = {Figaschewsky, Felix and K{\"u}hhorn, Arnold}, title = {An Inverse Approach to Identify Tuned Aerodynamic Damping, System Frequencies, and Mistuning, Part 1: Theory Under Rotating Conditions}, series = {Proceedings of the 15th International Symposium on Unsteady Aerodynamics, Aeroacoustics \& Aeroelasticity of Turbomachines, ISUAAAT15, 24-27 September 2018, University of Oxford, UK}, booktitle = {Proceedings of the 15th International Symposium on Unsteady Aerodynamics, Aeroacoustics \& Aeroelasticity of Turbomachines, ISUAAAT15, 24-27 September 2018, University of Oxford, UK}, publisher = {ISUAAAT Scientific Committee}, pages = {12}, language = {en} } @inproceedings{KochBeirowFilippatosetal., author = {Koch, Ilja and Beirow, Bernd and Filippatos, Angelos and K{\"u}hhorn, Arnold and Gude, Maik}, title = {Methodical Approach for Simulation the Vibration of Damaged Fibre Reinforced Composite Rotors Under Consideration of Aerodynamic Influences}, series = {18th European Conference on Composite Materials (ECCM18), Athen (Griechenland), 25.-28. Juni 2018}, booktitle = {18th European Conference on Composite Materials (ECCM18), Athen (Griechenland), 25.-28. Juni 2018}, pages = {8}, language = {en} } @inproceedings{BeirowKuehhornFigaschewskyetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Figaschewsky, Felix and Bornholm, Alfons and Repetckii, Oleg V.}, title = {Forced Response Reduction of a Blisk by Means of Intentional Mistuning}, series = {ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, Volume 7C: Structures and Dynamics, Oslo, Norway, June 11-15, 2018}, booktitle = {ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition, Volume 7C: Structures and Dynamics, Oslo, Norway, June 11-15, 2018}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5115-9}, doi = {10.1115/GT2018-76584}, pages = {10}, abstract = {The effect of intentional mistuning has been analyzed for an axial turbocharger blisk with the objective of limiting the forced response due to low engine order excitation (LEO). The idea behind the approach was to increase the aerodynamic damping for the most critical fundamental mode in a way that a safe operation is ensured without severely losing aerodynamic performance. Apart from alternate mistuning a more effective mistuning pattern is investigated, which has been derived by means of optimization employing genetic algorithms. In order to keep the manufacturing effort as small as possible only two blade different geometries have been allowed which means that an integer optimization problem has been formulated. Two blisk prototypes have been manufactured for the purpose of demonstrating the benefit of the intentional mistuning pattern identified in this way: A first one with and a second one without employing intentional mistuning. The real mistuning of the prototypes has been experimentally identified. It is shown that the benefit regarding the forced response reduction is retained in spite of the negative impact of unavoidable additional mistuning due to the manufacturing process. Independently, further analyzes have been focused on the robustness of the solution by considering increasing random structural mistuning and aerodynamic mistuning as well. The latter one has been modeled by means of varying aerodynamic influence coefficients (AIC) as part of Monte Carlo simulations. Reduced order models have been employed for these purposes.}, language = {en} } @inproceedings{KoberKuehhornKeskin, author = {Kober, Markus and K{\"u}hhorn, Arnold and Keskin, Akin}, title = {Instability problems in implicit transient FEM simulations of fast rotating elastic structures - Description of the phenomenon and possible solutions}, series = {Proceedings of NAFEMS DACH Conference 2018, Bamberg, May 14-16, 2018}, booktitle = {Proceedings of NAFEMS DACH Conference 2018, Bamberg, May 14-16, 2018}, publisher = {NAFEMS Deutschland, {\"O}sterreich, Schweiz GmbH}, address = {Grafing}, isbn = {978-1-910643-14-3}, pages = {48 -- 52}, language = {en} } @inproceedings{WeberKuehhorn, author = {Weber, Robby and K{\"u}hhorn, Arnold}, title = {Mistuning und D{\"a}mpfung radialer Turbinen- und Verdichterlaufr{\"a}der}, series = {Abschluss- und Zwischenberichte der Forschungsstellen Turbomaschinen, Fr{\"u}hjahrstagung 2018, Tagungsband 2018, Bad Neuenahr}, booktitle = {Abschluss- und Zwischenberichte der Forschungsstellen Turbomaschinen, Fr{\"u}hjahrstagung 2018, Tagungsband 2018, Bad Neuenahr}, publisher = {Forschungsvereinigung Verbrennungskraftmaschinen e.V.}, address = {Frankfurt am Main}, pages = {159 -- 190}, language = {de} } @inproceedings{KoberKuehhornKeskin, author = {Kober, Markus and K{\"u}hhorn, Arnold and Keskin, Akin}, title = {Optimization of Newmark-Euler Time-Integration Parameters for a Stable and Efficient Implicit Simulation of Rotating Elastic Structures}, series = {Proceedings of 15th German LS-DYNA Forum}, booktitle = {Proceedings of 15th German LS-DYNA Forum}, publisher = {DYNAmore GmbH}, address = {Stuttgart}, isbn = {978-3-9816215-5-6}, pages = {235 -- 238}, language = {en} } @inproceedings{FigaschewskyKuehhornGiersch, author = {Figaschewsky, Felix and K{\"u}hhorn, Arnold and Giersch, Thomas}, title = {A Finite Element Based Least Square Fit for the Assessment of Integral and Non-Integral Vibrations With Blade Tip Timing}, series = {Proceedings of ISROMAC 2017, Maui, Hawaii, December 16-21, 2017}, booktitle = {Proceedings of ISROMAC 2017, Maui, Hawaii, December 16-21, 2017}, pages = {9}, abstract = {This paper aims at improving the robustness and accuracy of the least square fit technique utilized in blade tip timing (BTT) measurements of blade vibrations by proposing two modifications. The first proposal is to replace the lines of the original least square problem by differences of consecutive lines. Thereby, the static deflection as well as the circumferential blade positioning error cancels out and the robustness is improved by removing these uncertainties inherently. The second proposal is to replace the fit of piecewise constant vibration amplitudes within the chosen block length by a linear or cubic spline in the frequency (integral) or time (non-integral) regime. This does not only suppress overshoots due to distorted acceleration or deceleration manoeuvres but also allows for a "coarser analysis grid" (i.e. larger block length) without loosing amplitude accuracy. Thereby it smooths out random errors more efficiently and increases the orthogonality of the relevant EO or vibration frequency to unwanted signal components.}, language = {en} } @inproceedings{BeirowFigaschewskyKuehhornetal., author = {Beirow, Bernd and Figaschewsky, Felix and K{\"u}hhorn, Arnold and Bornholm, Alfons}, title = {Vibration Analysis of an Axial Turbine Blisk with Optimized Intentional Mistuning Pattern}, series = {Proceedings of ISROMAC 2017, Maui, Hawaii, December 16-21, 2017}, booktitle = {Proceedings of ISROMAC 2017, Maui, Hawaii, December 16-21, 2017}, pages = {9}, abstract = {Aiming to limit the forced response of an axial turbine blisk for ship Diesel engine applications efforts have been made to increase the aerodynamic damping contribution for the most critical modes. In this regard the potential of intentional mistuning is investigated since it offers the opportunity to ensure a safe operation without a severe loss of aerodynamic performance. Genetic algorithms have been chosen to derive an optimized mistuning pattern. In order to keep the manufacturing effort within a limit only two possible blade geometries are allowed which means that an integer optimization problem has been formulated. For the purpose of demonstrating the benefit of the intentional mistuning pattern found, two blisk prototypes have been manufactured: One with and another one without employing intentional mistuning for purposes of comparison. Furthermore, this offers the opportunity for an experimental determination of mistuning being really manufactured and other modal properties as well. The experimental data basis is employed to update structural models which are well suited to demonstrate the forced response reduction under operational conditions.}, language = {en} } @inproceedings{HanschkeKuehhornSchrapeetal., author = {Hanschke, Benjamin and K{\"u}hhorn, Arnold and Schrape, Sven and Giersch, Thomas}, title = {Consequences of Borescope Blending Repairs on Modern HPC Blisk Aeroelasticity}, series = {Proceedings of ISROMAC 2017, Maui, Hawaii, December 16-21, 2017}, booktitle = {Proceedings of ISROMAC 2017, Maui, Hawaii, December 16-21, 2017}, pages = {8}, abstract = {Objective of this paper is to analyse the consequences of borescope blending repairs on the aeroelastic behaviour of a modern HPC blisk. To investigate the blending consequences in terms of aerodynamic damping and forcing changes, an exemplary blending of a rotor blade is modelled. Steady state flow parameters like total pressure ratio, polytropic efficiency and the loss coefficient are compared. Furthermore, aerodynamic damping is computed utilising the AIC approach for both geometries. Results are confirmed by SPF simulations for specific nodal diameters of interest. Finally, an unidirectional forced response analysis for the nominal and the blended rotor is conducted to determine the aerodynamic force exciting the blade motion. Fourier transformation of the forcing signal yields to the frequency content as well as the forcing amplitudes. As a result of the present analysis, the amplification of expected blade vibration amplitude is computed.}, language = {en} } @inproceedings{KoberKuehhornKeskinetal., author = {Kober, Markus and K{\"u}hhorn, Arnold and Keskin, Akin and Singh, Kai Navtej}, title = {Challenges and opportunities of thermomechanical FEM simulations of high fidelity aero-engine models by implicit time-integration}, series = {Proceedings of ISABE 2017, ISABE-2017-22568, Manchester, September 3.-8., 2017}, booktitle = {Proceedings of ISABE 2017, ISABE-2017-22568, Manchester, September 3.-8., 2017}, publisher = {ISABE}, pages = {10}, language = {en} } @inproceedings{FigaschewskyKuehhornBeirowetal., author = {Figaschewsky, Felix and K{\"u}hhorn, Arnold and Beirow, Bernd and Giersch, Thomas and Schrape, Sven}, title = {Analysis of Mistuned Forced Response in an Axial High Pressure Compressor Rig With Focus on Tyler-Sofrin Modes}, series = {ISABE 2017, ISABE-2017-22614, Manchester, September 3.-8., 2017}, booktitle = {ISABE 2017, ISABE-2017-22614, Manchester, September 3.-8., 2017}, publisher = {ISABE}, pages = {21}, language = {en} } @inproceedings{BeirowKuehhornFigaschewskyetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Figaschewsky, Felix and H{\"o}nisch, Peter and Giersch, Thomas and Schrape, Sven}, title = {Model Update and Validation of a Mistuned High Pressure Compressor Blisk}, series = {Proceedings of ISABE 2017, ISABE-2017-22568, Manchester, September 3.-8., 2017}, booktitle = {Proceedings of ISABE 2017, ISABE-2017-22568, Manchester, September 3.-8., 2017}, publisher = {ISABE}, pages = {14}, language = {en} } @inproceedings{FigaschewskyGierschKuehhorn, author = {Figaschewsky, Felix and Giersch, Thomas and K{\"u}hhorn, Arnold}, title = {Forced Response Prediction of an Axial Turbine Rotor With Regard to Aerodynamically Mistuned Excitation}, series = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics, D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-25896}, booktitle = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics, D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-25896}, publisher = {ASME}, isbn = {978-0-7918-4577-6}, doi = {10.1115/GT2014-25896}, pages = {13}, abstract = {The design of both efficient and reliable turbomachinery blades demands a detailed knowledge of static and dynamic forces during operation. This paper aims to contribute to the proper identification of dynamic excitation mechanisms acting on an axial turbine rotor, particularly with regard to deviations of the NGV's nominal geometry due to the use of variable vanes or tolerances in manufacturing. As variations of the NGV's geometry disturb the perfectly periodic pattern of the downstream flow features, other spectral components than those correlated with the number of stator vanes are possible to appear. These frequency components may lead to low engine order excitation of fundamental blade modes at high engine speeds. Under these operating conditions the rotor is already highly loaded with centrifugal forces and additional dynamic excitation may cause unacceptable stresses. Thus aerodynamic mistuning might be a limiting criterion for the design of a highly loaded turbine rotor. Within this paper 2 dimensional CFD-models are used to investigate both, the determination of the wake of a geometric mistuned stator guide vane and the influence of the resulting excitation on the adjacent rotor stage due to aerodynamically mistuned flow. In order to generate a mistuned NGV geometry, variations of pitch and stagger angle are taken into account and a mesh morpher is used to produce computational domains of the mistuned geometry on the basis of a nominal mesh. Additionally a simplified reconstruction process based on a set of CFD computations will be introduced, being able to reproduce the spectral components of the mistuned wake by specifying a certain geometric mistuning distribution. The prediction of the resulting modal forces is carried out in time domain and approaches with lower fidelity are investigated with respect to their capability of reproducing the key features of an aerodynamically mistuned excitation mechanism.}, language = {en} } @inproceedings{RauerKuehhornSpringmann, author = {Rauer, Georg and K{\"u}hhorn, Arnold and Springmann, Marcel}, title = {Residual Stress Modelling and Inverse Heat Transfer Coefficients Estimation of a Nickel-Based Superalloy Disc Forging}, series = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 6, D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-25827}, booktitle = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 6, D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-25827}, publisher = {ASME}, isbn = {978-0-7918-4575-2}, doi = {10.1115/GT2014-25827}, abstract = {Aero engine disc forgings are subjected to heat treatment operations, i.e., solution treatment followed by quenching and artificial aging, with the aim of achieving improved mechanical material properties. During heat treatment high inhomogeneous temperature gradients and long loading times at elevated temperatures occur and lead to the development and partial relaxation of bulk residual stresses. The intention of this paper is to describe the residual stress modelling of a nickel-based ATI 718Plus® superalloy disc forging. For this purpose, an uncoupled thermomechanical finite element problem is solved consisting of a thermal model based on transient, spatially varying heat transfer coefficients (HTCs) and a stress model incorporating the nonlinear material behaviour to account for thermal induced inelastic deformations. A graphical user interface based application has been created for the automatic estimation of the a priori unknown HTCs by using a serial solution procedure for the two dimensional inverse heat conduction problem (IHCP) based on the function specification method. The estimated temperature fields have been compared at the thermocouple positions with the corresponding measurement data and confirm the suitability of the inverse algorithm to this problem. A rate-independent elasto-plastic constitutive model is used to simulate the residual stress formation while quenching the disc forging. Two creep models have been adjusted to uniaxial tensile test data and applied to simulate the stress relaxation during aging. Finally, this paper presents the numerical results of the stress analysis. Copyright © 2014 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @inproceedings{BeirowKuehhornGierschetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Giersch, Thomas and Nipkau, Jens}, title = {Optimization-Aided Forced Response Analysis of a Mistuned Compressor Blisk}, series = {ASME Turbo Expo 2014, Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics, D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-25915}, booktitle = {ASME Turbo Expo 2014, Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics, D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-25915}, publisher = {ASME}, isbn = {978-0-7918-4577-6}, doi = {10.1115/GT2014-25915}, pages = {11}, abstract = {The forced response of the first rotor of an E3E-type high pressure compressor blisk is analyzed with regard to varying mistuning, varying engine order excitations and the consideration of aeroelastic effects. For that purpose, SNM-based reduced order models are used in which the disk remains unchanged while the Young's modulus of each blade is used to define experimentally adjusted as well as intentional mistuning patterns. The aerodynamic influence coefficient technique is employed to model aeroelastic interactions. Furthermore, based on optimization analyses and depending on the exciting EO and aerodynamic influences it is searched for the worst as well as the best mistuning distributions with respect to the maximum blade displacement. Genetic algorithms using blade stiffness variations as vector of design variables and the maximum blade displacement as objective function are applied. An allowed limit of the blades' Young's modulus standard deviation is formulated as secondary condition. In particular, the question is addressed if and how far the aeroelastic impact, mainly causing aerodynamic damping, combined with mistuning can even yield a reduction of the forced response compared to the ideally tuned blisk. It is shown that the strong dependence of the aerodynamic damping on the inter-blade phase angle is the main driver for a possible response attenuation considering the fundamental blade mode. The results of the optimization analyses are compared to the forced response due to real, experimentally determined frequency mistuning as well as intentional mistuning. Copyright © 2014 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @inproceedings{GierschFigaschewskyHoenischetal., author = {Giersch, Thomas and Figaschewsky, Felix and H{\"o}nisch, Peter and K{\"u}hhorn, Arnold and Schrape, Sven}, title = {Numerical Analysis and Validation of the Rotor Blade Vibration Response Induced by High Pressure Compressor Deep Surge}, series = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-26295}, booktitle = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-26295}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4577-6}, doi = {10.1115/GT2014-26295}, pages = {12}, abstract = {The following paper presents a numerical analysis of a deep surge cycle of a 4.5 stage research compressor. The resulting unsteady loads are used to determine the response of two particular rotor blade rows that are then compared to strain gauge data from measurements. Within a deep surge cycle the compressor experiences a rapid change of the flow field from forward to reversed flow. This rapid breakdown is linked to a new mean blade load. Hence, the rapid change in blade loads are able to excite fundamental blade modes similar to an impulse load. The resulting vibration magnitudes might reach critical levels. This paper demonstrates two different approaches to evaluate the unsteady flow during a surge cycle. The first uses a three dimensional, time accurate finite volume solver for viscid compressible flows to calculate the transient surge cycle of the compressor. The compressor itself is represented by a multi-blade-row sector model. The second approach makes use of the same solver and compressor domain to determine steady state characteristics of the HPC in forward, stalled and reversed flow. Based on these characteristics an one dimensional finite volume solver for inviscid compressible flows was developed to determine the transient compressor behavior. The one dimensional solver represents the compressor by source terms that are linked to the previously determined steady state characteristics. Copyright © 2014 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @inproceedings{ReyVillazonWildowKuehhornetal., author = {Rey Villaz{\´o}n, Jos{\´e} Maria and Wildow, Toni and K{\"u}hhorn, Arnold and Benton, Robert and G{\"o}hler, Moritz}, title = {Impact of the Secondary Air System Design Parameters on the Calculation of Turbine Discs Windage}, series = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 5C: Heat Transfer, D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-26050}, booktitle = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 5C: Heat Transfer, D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-26050}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4573-8}, doi = {10.1115/GT2014-26050}, pages = {9}, abstract = {The rotating components in gas turbines are very highly stressed as a result of the centrifugal and thermal loads. One of the main functions of the secondary air system (SAS) is to ensure that the rotating components are surrounded by air that optimizes disc lifing and integrity. The SAS is also responsible for the blade cooling flow supply, preventing hot gas ingestion from the main annulus into the rotor-stator cavities, and for balancing the net axial load in the thrust bearings. Thus, the SAS design requires a multidisciplinary compromise to provide the above functions, while minimizing the penalty of the secondary flows on engine performance. The phenomenon known as rotor-stator drag or windage is defined as the power of the rotor moment acting on its environment. The power loss due to windage has a direct impact on the performance of the turbine and the overall efficiency of the engine. This paper describes a novel preliminary design approach to calculate the windage of the rotor-stator cavities in the front of a typical aero engine HP turbine. The new method is applied to investigate the impact of the SAS design parameters on the windage losses and on the properties of the cooling flows leading to the main annulus. Initially, a theoretical approach is followed to calculate the power losses of each part of the HPT front air feed system. Then, a 1D-network integral model of the cavities and flow passages of the HPT front is built and enhanced with detailed flow field correlations. The new 1D-flow network model offers higher fidelity regarding local effects. A result comparison between the theoretical calculation and the prediction of the enhanced flow network model puts forward the relevance of the local flow field effects in the design concept of the SAS. Using the enhanced 1D-flow network models, the SAS design parameters are varied to assess their influence on the windage and pumping power calculation. As a conclusion, the paper shows how the SAS design can have a significant influence on the HPT overall power and the air that is fed back into the turbine blade rows. Controlling these features is essential to bid a competitive technology in the aero engine industry. Copyright © 2014 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @inproceedings{BeirowMaywaldKuehhorn, author = {Beirow, Bernd and Maywald, Thomas and K{\"u}hhorn, Arnold}, title = {Mistuning and Damping Analysis of a Radial Turbine Blisk in Varying Ambient Conditions}, series = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-25521}, booktitle = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-25521}, publisher = {ASME}, isbn = {978-0-7918-4577-6}, doi = {10.1115/GT2014-25521}, abstract = {A mistuned radial turbine impeller is analyzed with respect to the impact of varying ambient pressures and temperatures as well on frequency response functions and modal damping ratios. Beginning at room conditions, a finite element model of an impeller wheel at rest is updated based on experimentally determined mistuning in terms of blade dominated frequencies. The following numerical forced response analyses yield a maximum blade displacement amplification of 67\% compared to the tuned reference. In addition, modal damping ratios are determined in dependence on the ambient pressure ranging from technical vacuum at 1 mbar up to 6000 mbar in a pressure chamber. Shaker excitation and laser Doppler vibrometry response measurement is employed in this context. A linear dependence of modal damping ratios on ambient pressure and a dominating damping contribution of the surrounding air even for higher modes could be proved. Moreover, the experimental determination of frequency response functions (FRF) at technical vacuum yields a better separation of resonance peaks compared to room conditions at 1013 mbar and hence, this data allows for more accurate model-updates in principle. It is proved that numerical models updated regarding mistuning at room conditions are well suited to predict the forced response at arbitrary pressures if measured modal damping ratios at these pressures are considered. Finally, within analyzing the effect of increasing structural temperatures with the surrounding air at 1013 mbar included slightly decreasing resonance frequencies but strongly increasing FRF-amplitudes are determined. Copyright © 2014 by ASME}, language = {en} } @inproceedings{BehnamKuehhorn, author = {Behnam, Nouri and K{\"u}hhorn, Arnold}, title = {Automated CAE process for thermo-mechanical lifing prediction of a parameterized turbine blade with internal cooling}, series = {Joined 11th World Congress on Computational Mechanics (WCCM XI), 5th European Conference on Computational Mechanics (ECCM V), 6th European Conference on Computational Fluid Dynamics (ECFD VI) conference}, booktitle = {Joined 11th World Congress on Computational Mechanics (WCCM XI), 5th European Conference on Computational Mechanics (ECCM V), 6th European Conference on Computational Fluid Dynamics (ECFD VI) conference}, language = {en} } @inproceedings{ReyVillazonKuehhorn, author = {Rey Villaz{\´o}n, Jos{\´e} Maria and K{\"u}hhorn, Arnold}, title = {Adaptive CFD-Enhanced Windage Modelling for Aero Engine Turbine Rotor-Stator Cavities}, series = {Joined 11th World Congress on Computational Mechanics (WCCM XI), 5th European Conference on Computational Mechanics (ECCM V), 6th European Conference on Computational Fluid Dynamics (ECFD VI) conference}, booktitle = {Joined 11th World Congress on Computational Mechanics (WCCM XI), 5th European Conference on Computational Mechanics (ECCM V), 6th European Conference on Computational Fluid Dynamics (ECFD VI) conference}, language = {en} } @inproceedings{BehnamKuehhorn, author = {Behnam, Nouri and K{\"u}hhorn, Arnold}, title = {Interdisciplinary Analysis of a Turbine Blade With Internal Cooling Including Local Distribution and Rotation Effects}, series = {11th AIAA/ASME Joint Thermophysics and Heat Transfer Conference, Atlanta, GA}, booktitle = {11th AIAA/ASME Joint Thermophysics and Heat Transfer Conference, Atlanta, GA}, publisher = {AIAA}, address = {Reston, VA}, isbn = {978-1-62410-281-3}, pages = {16}, language = {en} } @inproceedings{BeirowKuehhornGolzeetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Golze, Mark and Klauke, Thomas}, title = {Experimentelle Untersuchungen des strukturdynamischen Verhaltens von Hochdruckverdichterschaufeln in Integralbauweise (Blisks) mittels Laser-Doppler-Vibrometrie}, language = {de} } @inproceedings{ReyVillazonBertholdKuehhorn, author = {Rey Villaz{\´o}n, Jos{\´e} Maria and Berthold, Martin and K{\"u}hhorn, Arnold}, title = {Adaptive Flow Field Thermal Modeling Techniques for Turbine Rotor-Stator Cavities}, series = {Proceedings of ASME Turbo Expo 2013, San Antonio, Texas, USA , June 3-7, 2013, Vol. 3C: Heat Transfer, Paper GT2013-94845}, booktitle = {Proceedings of ASME Turbo Expo 2013, San Antonio, Texas, USA , June 3-7, 2013, Vol. 3C: Heat Transfer, Paper GT2013-94845}, publisher = {ASME}, address = {New York}, isbn = {978-0-7918-5516-4}, doi = {10.1115/GT2013-94845}, pages = {11}, language = {en} } @inproceedings{SpringmannScherzerKunaetal., author = {Springmann, Marcel and Scherzer, M. and Kuna, M. and K{\"u}hhorn, Arnold}, title = {Numerical simulation of localization phenomena in the frame of damage parameter identification}, series = {Seminar: Materials modeling, FE simulations of the behavior of modern industrial materials including failure, 5th - 6th December 2006, Niedernhausen (Wiesbaden), Germany}, booktitle = {Seminar: Materials modeling, FE simulations of the behavior of modern industrial materials including failure, 5th - 6th December 2006, Niedernhausen (Wiesbaden), Germany}, publisher = {NAFEMS Contact Nordic Countries}, address = {Grafing b. M{\"u}nchen}, isbn = {1-874376-19-0}, language = {en} } @misc{WeberKuehhornKlaukeetal., author = {Weber, Robby and K{\"u}hhorn, Arnold and Klauke, Thomas and Schrape, Sven}, title = {The Effect of Sand Erosion on a Compressor Blade and its Modal Properties}, series = {Proceedings of ASME Turbo Expo 2020, Turbomachinery Technical Conference and Exposition, GT2020, September 21-25, 2020, Virtual, Online}, journal = {Proceedings of ASME Turbo Expo 2020, Turbomachinery Technical Conference and Exposition, GT2020, September 21-25, 2020, Virtual, Online}, pages = {9}, abstract = {The wear and damage of High-Pressure Compressor (HPC) blades due to erosion or Foreign Object Damage (FOD) have a significant influence on HPC aerodynamic performance, vibration resistance against High-Cycle Fatigue (HCF) and thus component lifetime. The changes in airfoil geometry reduce the overall engine efficiency. Furthermore extended off-wing engine maintenances due to blade failures are increasing the cost of ownership. The safe operation of every engine within a reduced number of shop visits requires a reliable prediction of future deterioration. This enables the optimization of services and off-wing time. One contribution to this is a better understanding of the component's dynamics and based on this providing an improved wear modeling to reliably predict the remaining lifetime and the decreased efficiency. This contribution determines the material removal of HPC blades due to sand erosion. Originally, this stage was built as a blisk (Blade Integrated Disk). After sand erosion test completion, the blisk was cut into segments containing one airfoil only. First, the material removal is determined for ten blades of one exemplary rotor. A blue light fringe projector is employed to identify the geometrical differences between the eroded blades and the nominal design. Second, realistic finite element models are generated to enable comparable modal analyses of eroded blades. This procedure suffers from unavoidable and mostly random imperfections due to the manufacturing process, which significantly affects the blade surface before the erosion test can be conducted. Therefore, an already published approach is implemented in the third step to predict the blade surface after erosion based on nominal blade design. The investigation is completed by comparing measured and predicted surfaces. Finally, the aforementioned tool is employed to predict the locations and intensities of the material losses and the accompanying change in modal properties of this compressor blade concerning operational time.}, language = {de} } @inproceedings{KeskinKoberStelldingeretal., author = {Keskin, Akin and Kober, Markus and Stelldinger, Enrico and K{\"u}hhorn, Arnold and B{\"o}hm, Holger and Hornig, Andreas and Hufenbach, Werner}, title = {On the quantification of errors of a pre-processing effort reducing contact meshing approach : AIAA 2015-0408}, series = {53rd AIAA Aerospace Sciences Meeting 2015, Kissimmee, Florida, USA, 5 - 9 January 2015, held at the AIAA SciTech Forum 2015, vol. 4}, booktitle = {53rd AIAA Aerospace Sciences Meeting 2015, Kissimmee, Florida, USA, 5 - 9 January 2015, held at the AIAA SciTech Forum 2015, vol. 4}, publisher = {Curran}, address = {Red Hook, NY}, isbn = {978-1-5108-0117-2}, doi = {10.2514/6.2015-0408}, pages = {3113 -- 3124}, language = {en} } @inproceedings{ReyVillazonWildowKuehhornetal., author = {Rey Villaz{\´o}n, Jos{\´e} Maria and Wildow, Toni and K{\"u}hhorn, Arnold and Benton, Robert and Eydam, Tobias}, title = {Advanced Turbine Preliminary Design Environment for the automatic Generation of Secondary Air System Models}, series = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 7A: Structures and Dynamics Montreal, Quebec, Canada, June 15-19, 2015}, booktitle = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 7A: Structures and Dynamics Montreal, Quebec, Canada, June 15-19, 2015}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5676-5}, doi = {10.1115/GT2015-42661}, abstract = {The design and development process of an aero engine is a complex and time-consuming task that involves many disciplines and company departments with different objectives and requirements. Along the preliminary design phase, multiple concepts are assessed in order to select a competitive technology. The engine design process, which was traditionally subdivided into modular component tasks, is nowadays considered as a multi-disciplinary workflow. Having recognized the need for developing advanced turbine preliminary design tools, this work focuses on enhancing the integration of turbine design disciplines, improving the accuracy of models and speeding the time to generate models. The proposed process facilitates an automated turbine Secondary Air System (SAS) and turbine discs concept definition. Furthermore, the process of CAD models and flow network models generation is accelerated via automation of the engineering workflow. This is accomplished through a novel Java based data model, where the design of turbine discs and SAS features is captured in a programmable framework. In the application section, the preliminary design definition of a reference HP turbine subsystem is replicated using the newly developed common design environment. The automated workflow is then used to generate the corresponding CAD models, recognize the subsystem flow network, and generate the 1D flow network model. The results are then compared to the experimentally validated model of a reference engine. As conclusion, the automated workflow offers a quick and parametric model generation process, while providing a good level of fidelity for the preliminary design phase. Copyright © 2015 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @inproceedings{WagnerKuehhorn, author = {Wagner, Frank and K{\"u}hhorn, Arnold}, title = {Response surface based robust design optimization on the example of a high pressure turbine blade}, series = {8. Dresdner Probabilistik-Workshop, Technische Universit{\"a}t Dresden, 08.-09. Okt. 2015}, booktitle = {8. Dresdner Probabilistik-Workshop, Technische Universit{\"a}t Dresden, 08.-09. Okt. 2015}, address = {Dresden}, pages = {18}, abstract = {Nowadays in a product design process the manufacturing tolerances have to be considered. Therefore a deterministic optimization needs to be converted into a robust design optimization. Usually the reference geometry is represented by a parametric model and an appropriate set of default parameters. In the robust design approach this set is replaced by a set of distributed parameters. These distributions are known from a previous design or needs to be estimated. This work is about a robust design and multi objective optimization of a high pressure turbine blade (first row) from an actual aero engine. The multidisciplinary objectives are the combined life of the aero-foil (LCF and creep) for the outer and inner geometry, the efficiency and the mass of the blade. For the input set different kinds of parameter will be examined. Apart from the major geometry parameters, which represent the external surface of the blade, parameters for material and boundary conditions will be investigated as well. The used workflow contains the Rolls-Royce tool parablading for the creation of the external aero-foil, Siemens NX for general geometry manipulation, Hydra as Navier-Stokes solver and SC03 for the structural problem and is set up in the automation software ISight. Focus of this work is the creation of response surfaces and physical integrity of the delivered results. Therefore, different validation criteria will be consulted. These are implemented in a Matlab toolbox and tested on typical optimization test problems. Based on the validated response surfaces a huge number of evaluations is possible, which is necessary for a robust design optimization. As the major result a set of Pareto optimal designs will be delivered.}, language = {en} } @inproceedings{GierschKuehhornFigaschewsky, author = {Giersch, Thomas and K{\"u}hhorn, Arnold and Figaschewsky, Felix}, title = {Probabilistic Analysis of Low Engine Order Excitation Due to Geometric Perturbations of Upstream Nozzle Guide Vanes : ISABE-2015-20165}, series = {Conference Proceedings from the 22nd International Symposium on Air Breathing Engines, October 25-30, 2015, Phoenix, Arizona}, booktitle = {Conference Proceedings from the 22nd International Symposium on Air Breathing Engines, October 25-30, 2015, Phoenix, Arizona}, publisher = {ISABE}, pages = {1 -- 9}, language = {en} } @inproceedings{MaywaldBeirowHeinrichetal., author = {Maywald, Thomas and Beirow, Bernd and Heinrich, Christoph Rocky and K{\"u}hhorn, Arnold}, title = {Vacuum Spin Test Series of a Turbine Impeller with Focus on Mistuning and Damping by Comparing Tip Timing and Strain Gauge Results}, series = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 7B: Structures and Dynamics Montreal, Quebec, Canada, June 15-19, 2015}, booktitle = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 7B: Structures and Dynamics Montreal, Quebec, Canada, June 15-19, 2015}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5677-2}, doi = {10.1115/GT2015-42649}, abstract = {This paper describes preparation, execution and evaluation of a comprehensive bladed disk spin test series. At the example of an turbine impeller the effects of rotation and temperature are analyzed with special focus on mistuning and damping. The forced response is measured synchronously via 13 identical positioned strain gauges on each blade as well as via blade tip-timing. Subsequently it is possible to compare the results of both systems. During the test series rotational speed varies in the range from 10.000 up to 19.000 RPM. Simultaneously, the wheel is heated up to 820 K by an oven. A number of pre-selected natural frequencies, damping ratios and operating deflection shapes are evaluated and compared with respect to different rotational speeds and impeller temperatures. Copyright © 2015 by ASME}, language = {en} } @inproceedings{WagnerKuehhornParchem, author = {Wagner, Frank and K{\"u}hhorn, Arnold and Parchem, Roland}, title = {Robust design optimization applied to a high pressure turbine blade based on surrogate modelling techniques}, series = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 7A: Structures and Dynamics Montreal, Quebec, Canada, June 15-19, 2015}, booktitle = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 7A: Structures and Dynamics Montreal, Quebec, Canada, June 15-19, 2015}, isbn = {978-0-7918-5676-5}, doi = {10.1115/GT2015-42365}, abstract = {To achieve reverse objectives in engine design, advanced modelling and analysis methods are among the key research technologies. In the presented work, a robust design optimization of a first stage high pressure turbine blade has been carried out. This blade derives from a current production of a Rolls-Royce aero engine. The motivation of this work is to show that the methodology of robust design optimization can be applied to high pressure turbine blades. A fully automated workflow, which encapsulated the integral blade design and analysis process, has been used. The main workflow objective is a representative life value of the external surface of the blade. In addition, the workflow enables the engineering uses to consider sub objectives like mass, efficiency and life at critical locations of the blade. These can also be taken into account in the multi-objective robust design optimization. This research also focuses on the use of surrogate models, with attention to the delivery of a physically correct result. For this purpose, the validation of the applied methods has a huge significance and a toolbox was created to generate and evaluate the quality of the surrogate models. In the present case sixteen geometry parameters were considered. In order to show that this methodology is not limited to geometry variation, parameters for material specification and for boundary conditions were varied in addition. The surrogate model was trained by the workflow generated DoE-data and could be used for different kinds of optimization. As a conclusion, it has been demonstrated that the methodology can be used for the engineering design process of turbine blades, while delivering physically correct results. The different techniques for surrogate modelling were examined and compared. With the help of these surrogate models, an optimization of life, mass and efficiency with 22.5 million evaluations was possible. Finally, an overview of the methodology for the case of a real world turbine blade could be given, and an improved blade in the sense of multi-objective robust design was found. Copyright © 2015 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @inproceedings{BeirowKuehhornFigaschewskyetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Figaschewsky, Felix and Nipkau, Jens}, title = {Effect of Mistuning and Damping on the Forced Response of a Compressor Blisk Rotor}, series = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 7A: Structures and Dynamics Montreal, Quebec, Canada, June 15-19, 2015}, booktitle = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 7A: Structures and Dynamics Montreal, Quebec, Canada, June 15-19, 2015}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5677-2}, doi = {10.1115/GT2015-42036}, abstract = {The forced response of an E3E-type high pressure compressor blisk front rotor is analyzed with regard to intentional mistuning and its robustness towards additional random mistuning. Both a chosen alternating mistuning pattern and artificial mistuning patterns optimized concerning the forced response are considered. Focusing on three different blade modes, subset of nominal system mode-based reduced order models are employed to compute the forced response. The disk remains unchanged while the Young's modulus of each blade is used to define the particular mistuning pattern. The well established aerodynamic influence coefficient technique is employed to model aeroelastic coupling and hence to consider the strongly mode- and inter blade phase angle-dependent aerodynamic damping contribution. It has been found that a reduction of the maximum forced response beyond that of the tuned reference can be achieved for particular mistuning patterns and all modes considered. This implies an exciting engine order which would cause a low nodal diameter mode in case of a tuned blisk. At best a nearly 50\% reduction of maximum response magnitudes is computed for the fundamental bending mode and large mistuning. The solution proved to be robust towards additional random mistuning of reasonable magnitude, which is of particular interest with regard to a potential technical realization. In case of small mistuning as assumed for the first torsion and the longitudinal bending mode the advantage of achieving response magnitudes beyond the tuned reference gets lost indeed, if random mistuning is superimposed. However, mostly a lower response level is calculated compared to responses obtained from models adjusted to mistuning determined by experiment. Copyright © 2015 by ASME}, language = {en} } @inproceedings{FigaschewskyKuehhorn, author = {Figaschewsky, Felix and K{\"u}hhorn, Arnold}, title = {Analysis of Mistuned Blade Vibrations Based on Normally Distributed Blade Individual Natural Frequencies}, series = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 7B: Structures and Dynamics Montreal, Quebec, Canada, June 15-19, 2015}, booktitle = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 7B: Structures and Dynamics Montreal, Quebec, Canada, June 15-19, 2015}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5677-2}, doi = {10.1115/GT2015-43121}, abstract = {With increasing demands for reliability of modern turbomachinery blades the quantification of uncertainty and its impact on the designed product has become an important part of the development process. This paper aims to contribute to an improved approximation of expected vibration amplitudes of a mistuned rotor assembly under certain assumptions on the probability distribution of the blade's natural frequencies. A previously widely used lumped mass model is employed to represent the vibrational behavior of a cyclic symmetric structure. Aerodynamic coupling of the blades is considered based on the concept of influence coefficients leading to individual damping of the traveling wave modes. The natural frequencies of individual rotor blades are assumed to be normal distributed and the required variance could be estimated due to experiences with the applied manufacturing process. Under these conditions it is possible to derive the probability distribution of the off-diagonal terms in the mistuned equations of motions, that are responsible for the coupling of different circumferential modes. Knowing these distributions recent limits on the maximum attainable mistuned vibration amplitude are improved. The improvement is achieved due to the fact, that the maximum amplification depends on the mistuning strength. This improved limit can be used in the development process, as it could partly replace probabilistic studies with surrogate models of reduced order. The obtained results are verified with numerical simulations of the underlying structural model with random mistuning patterns based on a normal distribution of individual blade frequencies. Copyright © 2015 by ASME}, language = {en} } @misc{HardenbergKuehhornFanter, author = {Hardenberg, Alexander and K{\"u}hhorn, Arnold and Fanter, Maren}, title = {Bewertung der Auswirkungen von Strukturmodifikationen und Modellvereinfachungen unter Einsatz der FEA-FEA Korrelation auf das Modalverhalten einer Triebwerksgeh{\"a}usestruktur}, series = {2. VDI-Fachtagung Schwingungen 2019 : W{\"u}rzburg, 05. und 06. November 2019}, journal = {2. VDI-Fachtagung Schwingungen 2019 : W{\"u}rzburg, 05. und 06. November 2019}, publisher = {VDI-Verlag}, address = {D{\"u}sseldorf}, isbn = {978-3-18-092366-6}, language = {de} } @inproceedings{NouriLehmannKuehhorn, author = {Nouri, Behnam and Lehmann, Knut and K{\"u}hhorn, Arnold}, title = {Investigations on Nusselt Number Enhancement in Ribbed Rectangular Turbine Blade Cooling Channels of Different Aspect Ratios and Rotation Numbers}, series = {ASME Turbo Expo 2013: Turbine Technical Conference and Exposition, San Antonio, Texas, USA, June 3-7, 2013, Vol. 3A, Heat Transfer, Paper GT2013-94710}, booktitle = {ASME Turbo Expo 2013: Turbine Technical Conference and Exposition, San Antonio, Texas, USA, June 3-7, 2013, Vol. 3A, Heat Transfer, Paper GT2013-94710}, publisher = {ASME}, address = {New York}, isbn = {978-0-7918-5514-0}, doi = {10.1115/GT2013-94710}, pages = {11}, abstract = {In the drive for higher cycle efficiencies in gas turbine engines, turbine blades are seeing an increasingly high heat load. This in turn demands improvements in the internal cooling system and a better understanding of both the level and distribution of the internal heat-transfer. A typical approach to enhance the internal cooling of the turbine blade is by casting angled 'low blockage' ribs on the walls of the cooling channels. The objective of the present paper is to determine the detailed Nusselt number distribution in rectangular internal channels with ribs. This knowledge can be used to guide the overall design e.g. to achieve high levels of heat-transfer where required. The effects of rotation as well as the interaction effects of the position and direction of ribs on opposite walls of the cooling channel have been investigated. Numerical calculations have been carried out using the commercial CFD code Fluent to investigate the local Nusselt number enhancement factor in rectangular ducts of different aspect ratios (0.5, 1 and 2) which have 45° or 90° angled ribs located on two opposite walls. This has been studied for different Rotation number Ro (0-0.45) and with a Reynolds number >30000. The first series of studies has been carried out with the same experimental setup as by Han [1]. The geometry was slightly changed to avoid the effect of high heat transfer at the entry. This study identifies important vortical structures, which are dependent on the direction and the position of the ribs. This has a profound effect on the distribution of heat-transfer within the passage. It is shown that the two smooth walls of the duct have different average Nusselt number ratio Nu/NuFD enhancement depending on the rib angle. In addition, based on numerical investigations, simple correlations have been developed for the rotational influence of the internal Nusselt number distribution. A major finding is that the effect of rotation is dominant for low aspect ratio channels and the local enhancement due to the rib position and angle is more dominant for high aspect ratio channels.}, language = {en} } @inproceedings{BeirowKuehhornGierschetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Giersch, Thomas and Nipkau, Jens}, title = {Forced Response Analysis of a Mistuned Compressor Blisk}, series = {ASME Turbo Expo 2013: Turbine Technical Conference and Exposition, San Antonio, Texas, USA, June 3-7, 2013, Vol. 7B, Structures and Dynamics, Paper GT2013-94142}, booktitle = {ASME Turbo Expo 2013: Turbine Technical Conference and Exposition, San Antonio, Texas, USA, June 3-7, 2013, Vol. 7B, Structures and Dynamics, Paper GT2013-94142}, publisher = {ASME}, address = {New York}, isbn = {978-0-7918-5527-0}, doi = {10.1115/GT2013-94142}, pages = {10}, abstract = {The forced response of an E3E-type HPC-blisk front rotor is analyzed with regard to varying mistuning and the consideration of the fluid-structure interaction (FSI). For that purpose, a reduced order model is used in which the disk remains unchanged and mechanical properties of the blades namely stiffness and damping are adjusted to measured as well as intentional blade frequency mistuning distributions. The aerodynamic influence coefficient technique is employed to model the aeroelastics. Depending on the blade mode, the exciting engine order and aerodynamic influences it is sought for the worst mistuning distributions with respect to the maximum blade displacement based on optimization analyses. Genetic algorithms using blade alone frequencies as design variables are applied. The validity of the Whitehead-limit is assessed in this context. In particular, the question is addressed if and how far aeroelastic effects, mainly caused by aerodynamic damping, combined with mistuning can even cause a reduction of the forced response compared to the ideally tuned blisk. It is shown that the strong dependence of the aerodynamic damping on the inter-blade phase angle is the main driver for a possible response attenuation considering the fundamental as well as a higher blade mode. Furthermore, the differences to the blisk vibration response without a consideration of the flow and an increase of the disk's stiffness are discussed. Closing, the influence of pure damping mistuning is analyzed again using optimization.}, language = {en} } @inproceedings{PopigHoenischKuehhorn, author = {Popig, Frederik and H{\"o}nisch, Peter and K{\"u}hhorn, Arnold}, title = {Experimental and Numerical Analysis of Geometrical Induced Mistuning}, series = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 7B: Structures and Dynamics Montreal, Quebec, Canada, June 15-19, 2015}, booktitle = {ASME Turbo Expo 2015: Turbine Technical Conference and Exposition Volume 7B: Structures and Dynamics Montreal, Quebec, Canada, June 15-19, 2015}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5677-2}, doi = {10.1115/GT2015-43272}, abstract = {The application of high pressure compressor (HPC) rotors manufactured as blisk (Blade Integrated Disk) is ever-expanding in modern jet engine designs. Despite the major advantages of less mass and higher efficiency, the most challenging problem is lower mechanical damping due to the loss of damping between blades root's and the disk. Mistuning is induced by material inhomogeneities, manufacturing tolerances or wear during use and leads to amplitude magnification and mode localization. From the experimental point of view mistuning can be evaluated via experimental vibration analysis in terms of frequency deviations. Furthermore optical measurements can be evaluated in terms of geometrical deviations between the real and designed geometry. From the structural point of view a mistuned blisk model can be obtained by morphing the nodes of the geometrical tuned FE model or by performing blade individual stiffness mistuning due to modification of Young's modulus. The following work is focused on the numerical prediction of mistuned blisk vibrations. Therefore, the research blisk of the 4 stage research compressor, manufactured as job-production, is analyzed. For this research blisk optical measurement data as well as experimentally obtained frequency patterns are available. In a first part mistuning identification in terms of experimental vibration analysis and Proper Orthogonal Decomposition of the geometrical deviations is presented. In a second part mistuning modeling in terms of stiffness mistuning and geometrical mistuning is applied to the tuned FE-model and the numerical results are evaluated against experimental data regarding accuracy. Furthermore, the impact of geometrical deviations on mistuning is analyzed. Copyright © 2015 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @article{KuehhornBeirowGolzeetal., author = {K{\"u}hhorn, Arnold and Beirow, Bernd and Golze, Mark and Studener, Johannes}, title = {Strukturmechanische Analyse einer Triebwerksverdichter-Schaufelscheibe}, abstract = {Die Verbesserung von Kalibriermethoden f{\"u}r Hochdruckverdichterstufen in ausgef{\"u}hrter Integralbauweise verlangt von den Ingenieuren ein detaillierteres Verst{\"a}ndnis der strukturdynamischen Zusammenh{\"a}nge dieses komplexen Bauteils. Als Ausgangsbasis werden zun{\"a}chst f{\"u}r das perfekte Normdesign bei Ausnutzung der vorliegenden zyklischen Rotationssymmetrie numerische Ergebnisse vorgestellt. Dabei stehen bez{\"u}glich des Schwingverhaltens die Kopplungseffekte zwischen Scheibe und Schaufeln im Mittelpunkt, wobei experimentelle Untersu-chungen am realen Bauteil erg{\"a}nzend hinzugezogen werden. Zuk{\"u}nftig wird in einem weiteren Schritt im Rahmen erheblich aufwendigerer Berechnungen mit der Ber{\"u}cksichtigung von Imperfektionen hinsichtlich der filigranen Schaufeln die Rotationssymmetrie aufgegeben und somit die Basis f{\"u}r eine gezielte Beeinflussung des Schwingverhaltens infolge von Mistuning - Effekten geschaffen.}, language = {de} } @misc{WeberKuehhorn, author = {Weber, Robby and K{\"u}hhorn, Arnold}, title = {Mistuning und D{\"a}mpfung radialer Turbinen- und Verdichterlaufr{\"a}der}, series = {Abschluss- und Zwischenberichte der Forschungsstellen Turbomaschinen : Fr{\"u}hjahrstagung 2019 : Tagungsband : 2019 - W{\"u}rzburg}, journal = {Abschluss- und Zwischenberichte der Forschungsstellen Turbomaschinen : Fr{\"u}hjahrstagung 2019 : Tagungsband : 2019 - W{\"u}rzburg}, publisher = {Forschungsvereinigung Verbrennungskraftmaschinen e.V.}, address = {Frankfurt am Main}, pages = {75 -- 109}, abstract = {Abschlussbericht zum FVV-Projekt Mistuning und D{\"a}mpfung III}, language = {de} } @inproceedings{BeirowKuehhornGolzeetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Golze, Mark and Parchem, Roland and Johann, E.}, title = {Experimentelle und numerische Untersuchungen hinsichtlich einer Festigkeitsauslegungsoptimierung von Hochdruck-Verdichter-Schaufelscheiben unter besonderer Ber{\"u}cksichtigung von Mistuningeffekten}, series = {Deutscher Luft- und Raumfahrtkongress 2003, M{\"u}nchen, 17. bis 20. November 2003, Bd. 2}, booktitle = {Deutscher Luft- und Raumfahrtkongress 2003, M{\"u}nchen, 17. bis 20. November 2003, Bd. 2}, publisher = {DGLR}, address = {Bonn}, pages = {1495 -- 1504}, language = {de} } @inproceedings{KlaukeKuehhornGolzeetal., author = {Klauke, Thomas and K{\"u}hhorn, Arnold and Golze, Mark and Villwock, J. and Lenk, Olaf}, title = {Finite-Elemente-Anwendung neuerer Faserverbund-Bruchkriterien und deren Verifizierung mittels CFK-Bauteilpr{\"u}fung}, series = {Deutscher Luft- und Raumfahrtkongress 2003, M{\"u}nchen, 17. bis 20. November 2003, Bd. 1}, booktitle = {Deutscher Luft- und Raumfahrtkongress 2003, M{\"u}nchen, 17. bis 20. November 2003, Bd. 1}, publisher = {Dt. Ges. f{\"u}r Luft- und Raumfahrt}, address = {Bonn}, pages = {113 -- 120}, language = {de} } @inproceedings{StudenerKuehhorn, author = {Studener, Johannes and K{\"u}hhorn, Arnold}, title = {FE-Simulation des thermischen Aufheizvorganges eines Silizium-Wafers im RTA (Rapid Thermal Anneal) - Prozess}, series = {Tagungsband, 15. Deutschsprachige ABAQUS-Benutzerkonferenz, 22. - 23. September 2003, Fulda}, booktitle = {Tagungsband, 15. Deutschsprachige ABAQUS-Benutzerkonferenz, 22. - 23. September 2003, Fulda}, publisher = {ABAQUS Deutschland GmbH}, address = {Aachen [u.a.]}, language = {de} } @inproceedings{KoberKuehhornStelldingeretal., author = {Kober, Markus and K{\"u}hhorn, Arnold and Stelldinger, Enrico and Keskin, Akin}, title = {Considerations About the Necessary Mesh Density of Bearings in Detailed Finite Element Models}, series = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-25624}, booktitle = {ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, Volume 7B: Structures and Dynamics D{\"u}sseldorf, Germany, June 16-20, 2014, Paper GT2014-25624}, publisher = {ASME}, isbn = {978-0-7918-4577-6}, doi = {10.1115/GT2014-25624}, pages = {8}, abstract = {In order to predict properly the behavior of very complex mechanical models, much focus needs to be done on the level of model details as well as the techniques used to predict component movements based on mechanical and thermal loads. In particular bearings and joints play a significant role in big model assemblies such as aero-engines where most of the structures are modeled by solid elements rather than using traditional shell or beam elements. This approach is very complex and expensive in terms of computational effort however can lead to increased simulation accuracy when done properly. This publication will answer questions related to the modeling techniques required for detailed bearings (not only rotor bearings) and joints of an aero-engine application where these components are not idealized or simplified, i.e. the ball in a ball joint is meshed by solid elements. The investigation will discuss the question about the number of elements needed to mesh a ball joint in such a way that a correct rotation is possible. If the mesh is too coarse, a rotation would be impossible due to the faceting of the rotating parts. It will be shown that a proper rotation depends on a correct relation between the radius of the inner ball, the gap size of the bearing and the number of nodes in the circumferential direction. For this relation an analytical formula has been derived and successfully tested at some examples. Furthermore, some finite element codes offer the possibility of smoothed contact surfaces. These options improve the situation but they might cause issues too. For this reason these smoothed contact options are also considered under the aspects mentioned above. Copyright © 2014 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @misc{BeirowKuehhornWeberetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Weber, Robby and Popig, Frederik}, title = {Vibration Analyses of an Axial Turbine Wheel with Intentional Mistuning}, series = {Journal of Engineering for Gas Turbines and Power}, volume = {143}, journal = {Journal of Engineering for Gas Turbines and Power}, number = {6}, issn = {1528-8919}, doi = {10.1115/1.4049449}, abstract = {The last stage bladed disk of a steam turbine is analyzed with respect to both flutter susceptibility and limitation of forced response. Due to the lack of variable stator vanes unfavorable flow conditions may occur which increases the risk of flutter at part load conditions. For this reason, intentional mistuning is employed with the objective to prevent any self-excited vibrations. A first step in this direction is done by choosing alternate mistuning, which keeps the manufactural efforts in limits. In this sense, two different series of blades have been made. However, small deviations from the design intention are unavoidable due to the manufacturing procedure, which could be proved by bonk tests carried out earlier. The influence of these additional deviations is considered in numerical simulations. Moreover, the strong dependence of blade frequencies on the speed is taken into account since centrifugal stiffening effects significantly attenuate the blade-to-blade frequency difference. Focusing on the first flap mode it could be shown that a mitigation of flutter susceptibility is achieved by prescribing alternate mistuning, which indeed evokes an increase of originally small aerodynamic damping ratios. Nevertheless, the occurrence of negative damping ratios could not be completely precluded at part load conditions. That is why optimization studies are conducted based on genetic algorithms with the objective function of maximizing the lowest aerodynamic damping ratios. Finally, mistuning patterns could be identified featuring a tremendous increase of aerodynamic damping ratios. The robustness of the solutions could be proved by superimposing additional random mistuning.}, language = {en} } @misc{KlaukeKuehhornBeirowetal., author = {Klauke, Thomas and K{\"u}hhorn, Arnold and Beirow, Bernd and Golze, Mark}, title = {Numerical Investigations of Localized Vibrations of Mistuned Blade Integrated Disks (Blisks)}, language = {de} } @inproceedings{StelldingerKuehhornKober, author = {Stelldinger, Enrico and K{\"u}hhorn, Arnold and Kober, Markus}, title = {Otimization of a Carbon-fiber-reinforced Plastic Composite Structure using the Example of a Wing Rigger}, language = {en} } @inproceedings{BeirowKuehhornNipkau, author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Nipkau, Jens}, title = {An Equivalent Blisk Model Considering the Influence of the Air Flow on Blade Vibrations of a Mistuned Compressor Blisk}, series = {Vibration Problems ICOVP 2011, The 10th International Conference on Vibration Problems, The 10th International Conference on Vibration Problems}, booktitle = {Vibration Problems ICOVP 2011, The 10th International Conference on Vibration Problems, The 10th International Conference on Vibration Problems}, publisher = {Springer}, address = {Berlin [u.a.]}, isbn = {978-94-007-2068-8}, pages = {549 -- 555}, language = {en} } @inproceedings{NipkauKuehhornBeirow, author = {Nipkau, Jens and K{\"u}hhorn, Arnold and Beirow, Bernd}, title = {Modal and Aeroelastic Analysis of a Mistuned Compressor Blisk Using an Equivalent Blisk Model}, language = {en} } @inproceedings{BeirowNipkauKuehhorn, author = {Beirow, Bernd and Nipkau, Jens and K{\"u}hhorn, Arnold}, title = {Modal and Aeroelastic Analysis of a Compressor Blisk Considering Mistuning}, series = {Proceedings of the ASME Turbo Expo 2011, presented at the ASME 2011 Turbo Expo, June 6 - 10, 2011, Vancouver, British Columbia, Canada, Vol. 6, part B}, booktitle = {Proceedings of the ASME Turbo Expo 2011, presented at the ASME 2011 Turbo Expo, June 6 - 10, 2011, Vancouver, British Columbia, Canada, Vol. 6, part B}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5466-2}, pages = {1309 -- 1319}, language = {en} } @inproceedings{HoehnischKuehhornBeirow, author = {H{\"o}hnisch, Peter and K{\"u}hhorn, Arnold and Beirow, Bernd}, title = {Experimental and Numerical Analysis of Radial Turbine Bliks with Regard to Mistuning}, language = {en} } @misc{HeinrichKuehhornSteffetal., author = {Heinrich, Christoph Rocky and K{\"u}hhorn, Arnold and Steff, Klaus and Petry, Nico}, title = {Generalized Model for the Approximation of Coupled Acousto-Mechanical Natural Frequencies in High-Pressure Centrifugal Compressors}, series = {Journal of Engineering for Gas Turbines and Power}, journal = {Journal of Engineering for Gas Turbines and Power}, issn = {1528-8919}, doi = {10.1115/1.4049447}, pages = {27}, abstract = {The oil and gas, chemical, and process industries employ centrifugal compressors for a wide range of applications. Due to this, the conditions under which centrifugal compressors have to operate, vary significantly from case to case. Gas pipeline compressors, for example, may feature discharge pressures well over 100 bar. During the last decades, comprehensive research was conducted on the impact of high pressure operating conditions on the vibrational behavior of centrifugal compressors. Nowadays, it is well-known that an increase in gas pressure levels leads to a more pronounced interaction between the side cavities and the impeller, which results in a frequency shift of the acoustic and structural modes. For the safe operation of compressors, it is necessary to predict these coupled natural frequencies accurately. The state-of-the-art approach to achieve this objective is the finite element method. While this technique provides high-quality results, it incurs high computational costs and is, therefore, time-consuming. The authors of the current paper propose a generalized model to overcome this challenge. It uses the uncoupled modes of the impeller and side cavities in a modal superposition to approximate the coupled system's natural frequencies. In this way, the intended design geometries are considered while reducing the computational effort significantly. In a numerical study, the generalized model is applied to different systems of increasing complexity, and the results are compared to a finite element analysis. Finally, the paper concludes with a discussion of the limitations and benefits of all employed numerical methods.}, language = {en} } @inproceedings{KuehhornBeirowStrehlau, author = {K{\"u}hhorn, Arnold and Beirow, Bernd and Strehlau, Ulrik}, title = {Zum Schwingungsverhalten integraler Hochdruckverdichterlaufr{\"a}der}, language = {de} } @misc{GambittaKuehhornBeirowetal., author = {Gambitta, Marco and K{\"u}hhorn, Arnold and Beirow, Bernd and Schrape, Sven}, title = {Stator Blades Manufacturing Geometrical Variability in Axial Compressors and Impact on the Aeroelastic Excitation Forces}, series = {Journal of Turbomachinery}, volume = {144}, journal = {Journal of Turbomachinery}, issn = {1528-8900}, doi = {10.1115/1.4052602}, pages = {10}, abstract = {The manufacturing geometrical variability is a source of uncertainty, which cannot be avoided in the realization of machinery components. Deviations of a part geometry from its nominal design are inevitably present due to the manufacturing process. In the case of the aeroelastic forced response problem within axial compressors, these uncertainties may affect the vibration characteristics. For this reason, the impact of geometrical uncertainties due to the manufacturing process onto the modal forcing of axial compressor blades is investigated in this study. The research focuses on the vibrational behavior of an axial compressor rotor blisk. In particular, the amplitude of the forces acting as a source of excitation on the vibrating blades is studied. The geometrical variability of the upstream stator is investigated as input uncertainty. The variability is modeled starting from a series of optical surface scans. A stochastic model is created to represent the measured manufacturing geometrical deviations from the nominal model. A data reduction methodology is proposed in order to represent the uncertainty with a minimal set of variables. The manufacturing geometrical variability model allows to represent the input uncertainty and probabilistically evaluate its impact on the aeroelastic problem. An uncertainty quantification is performed in order to evaluate the resulting variability on the modal forcing acting on the vibrating rotor blades. Of particular interest is the possible rise of low engine orders due to the mistuned flow field along the annulus. A reconstruction algorithm allows the representation of the variability during one rotor revolution. The uncertainty on low harmonics of the modal rotor forcing can be therefore identified and quantified.}, language = {en} } @inproceedings{SpringmannKuehhornRaueretal., author = {Springmann, Marcel and K{\"u}hhorn, Arnold and Rauer, Georg and Giersch, Thomas}, title = {Constitutive Modelling of Plastic and Creep Behavior of the Nickel Base Superalloy ALLVAC® 718PLUS® under Heat Treatment Conditions}, language = {en} } @inproceedings{HoenischKuehhorn, author = {H{\"o}nisch, Peter and K{\"u}hhorn, Arnold}, title = {Mistuning und D{\"a}mpfung von Radialturbinen}, language = {de} } @misc{HanschkeKuehhornSchrapeetal., author = {Hanschke, Benjamin and K{\"u}hhorn, Arnold and Schrape, Sven and Giersch, Thomas}, title = {Consequences of Borescope Blending Repairs on Modern HPC Blisk Aeroelasticity}, series = {Journal of Turbomachinery}, volume = {141}, journal = {Journal of Turbomachinery}, number = {2}, issn = {1528-8900}, doi = {10.1115/1.4041672}, pages = {7}, abstract = {Objective of this paper is to analyze the consequences of borescope blending repairs on the aeroelastic behavior of a modern high pressure compressor (HPC) blisk. To investigate the blending consequences in terms of aerodynamic damping and forcing changes, a generic blending of a rotor blade is modeled. Steady-state flow parameters like total pressure ratio, polytropic efficiency, and the loss coefficient are compared. Furthermore, aerodynamic damping is computed utilizing the aerodynamic influence coefficient (AIC) approach for both geometries. Results are confirmed by single passage flutter (SPF) simulations for specific interblade phase angles (IBPA) of interest. Finally, a unidirectional forced response analysis for the nominal and the blended rotor is conducted to determine the aerodynamic force exciting the blade motion. The frequency content as well as the forcing amplitudes is obtained from Fourier transformation of the forcing signal. As a result of the present analysis, the change of the blade vibration amplitude is computed.}, language = {en} } @inproceedings{KuehhornBeirowParchemetal., author = {K{\"u}hhorn, Arnold and Beirow, Bernd and Parchem, Roland and Klauke, Thomas}, title = {Schaufelschwingungen bei realen Verdichter-Integralr{\"a}dern (BLISK)}, series = {Deutscher Luft- und Raumfahrtkongress 2006, Braunschweig, 06. bis 09. November 2006, Bd. 2}, booktitle = {Deutscher Luft- und Raumfahrtkongress 2006, Braunschweig, 06. bis 09. November 2006, Bd. 2}, publisher = {Dt. Ges. f{\"u}r Luft- und Raumfahrt}, address = {Bonn}, pages = {1199 -- 1208}, language = {de} } @misc{GambittaKuehhornBeirowetal., author = {Gambitta, Marco and K{\"u}hhorn, Arnold and Beirow, Bernd and Schrape, Sven}, title = {Stator Blades Manufacturing Geometrical Variability in Axial Compressors and Impact on the Aeroelastic Excitation Forces}, series = {Proceedings of ASME Turbo Expo 2021, ASME Paper Number: GT2021-59642}, journal = {Proceedings of ASME Turbo Expo 2021, ASME Paper Number: GT2021-59642}, abstract = {The manufacturing geometrical variability is a source of uncertainty, which cannot be avoided in the realization of a machinery. Deviations of a component geometry from its nominal design are inevitably present due to the manufacturing process. In the case of the aeroelastic forced response problem within axial compressors, these uncertainties may affect the vibration characteristics. For this reason, the impact of geometrical uncertainties due to the manufacturing process onto the modal forcing of axial compressor blades is investigated in this study. The research focuses on the vibrational behavior of an axial compressor rotor blisk (blade-integrated disk) and in particular the amplitude of the forces acting as source of excitation on the vibrating blades (modal forcing). Within this context, the geometry of the upstream stator plays an important role as in general the main harmonics of the rotor excitation forces are produced by its wake. Therefore, small variations of the upstream stators geometries, such as the ones caused by the manufacturing process, may affect the resulting forcing. In particular, the geometrical variability of the upstream stator implies that the hypothesis of a cyclic-symmetrical flow is no longer valid. This may cause the introduction of lower harmonic components in the modal forces, generally referred to as Low Engine Orders (LEO). The geometrical variability is modelled starting from a series of optical surface scans. A set of optical measurements of manufactured stator blades originating from the same nominal design constitutes the baseline dataset on which the geometrical model is built. The measured blades as well as the relative nominal geometry are parametrized to describe the individual blades surfaces. The parameterization is accomplished by slicing the surfaces in radial sections and describing each of these with a set of NACA-like parameters [1]. The measured geometrical deviations from the nominal model can therefore be described as an offset of such parameters. A reduced representation of the variables representing the input uncertainty (noise variables) is obtained via Principal Components Analysis. Afterwards a sampling on the reduced noise variables domain can be done to represent the modelled uncertainty and perform an Uncertainty Quantification (UQ) on the relative quantities of interest, in this case the modal forcing. The computation of the modal forcing is done through a CFD solver, computing the unsteady flow field around the rotor blades. The domain considered in this case is a 1.5 stage of the axial compressor, including the rotor and the up- and down-stream stators. The solutions are initialized from a validated steady state solution of the considered compressor rig. The time-dependent pressure field calculated on the rotor blades is projected onto the relative vibrational mode shapes of interests (from structural modal analyzes). The resulting forces are analyzed by means of their spectrum, evaluating the amplitudes for the present engine orders (higher harmonics of the shaft mechanical speed). The UQ uses Monte Carlo methods to evaluate the impact of the geometrical variability onto the modal forcing. The modelled uncertainty on the geometries is introduced into the CFD solver to compute the deviations on the quantities of interest. A reconstruction of the forces acting on the rotor during one revolution is obtained. This allows to evaluate the uncertainty on the present engine orders as well as the possible rise of LEO for the rotor blades in presence of a mistuned upstream stator. [1]: Lange A., Vogeler K., G{\"u}mmer V., Schrapp H. and Clemen C. (2009). "Introduction of a Parameter Based Compressor Blade Model for Considering Measured Geometry Uncertainties in Numerical Simulation." Proceedings of ASME Turbo Expo. GT2009-59937}, language = {en} } @inproceedings{NipkauKuehhornSchrape, author = {Nipkau, Jens and K{\"u}hhorn, Arnold and Schrape, S.}, title = {Determination of Aeroelastic Parameters of a High-Pressure-Compressor Stage using Fluid-Structure Interaction Calculations}, series = {Seminar: Simulation of Complex Flows (CFD), applications and trends, 10th - 11th March 2008, Wiesbaden, Germany}, booktitle = {Seminar: Simulation of Complex Flows (CFD), applications and trends, 10th - 11th March 2008, Wiesbaden, Germany}, publisher = {NAFEMS Contact DACH \& Nordic Countries}, address = {Bernau am Chiemsee}, isbn = {978-1-87437-633-0}, language = {en} } @misc{NaveedKuehhorn, author = {Naveed, Zishan and K{\"u}hhorn, Arnold}, title = {An Isogeometric Based Study of Contact Behaviour for Rotating Structures}, series = {14th World Congress on Computational Mechanics (WCCM)-ECCOMAS Congress 2020, Virtual Conference: 11-15 January 2021}, journal = {14th World Congress on Computational Mechanics (WCCM)-ECCOMAS Congress 2020, Virtual Conference: 11-15 January 2021}, language = {en} } @incollection{SchrapeKuehhornGolze, author = {Schrape, S. and K{\"u}hhorn, Arnold and Golze, Mark}, title = {Simulation fluidged{\"a}mpfter Strukturschwingungen durch partitionierte Fluid-Struktur-Kopplung mittels MpCCI}, language = {de} } @article{SchrapeKuehhornGolze, author = {Schrape, S. and K{\"u}hhorn, Arnold and Golze, Mark}, title = {Simulation fluidged{\"a}mpfter Strukturschwingungen mittels partitioniertem Kopplungssatz via MpCCI}, series = {NAFEMS-Magazin}, volume = {2}, journal = {NAFEMS-Magazin}, number = {4}, pages = {41 -- 49}, language = {de} } @incollection{SchrapeKuehhornGolze, author = {Schrape, S. and K{\"u}hhorn, Arnold and Golze, Mark}, title = {Simulation of fluid damped structural vibrations}, series = {Proceedings, 7th MpCCI User Forum, February 21st and 22nd 2006, at Schloss Birlinghoven, Sankt Augustin, Germany}, booktitle = {Proceedings, 7th MpCCI User Forum, February 21st and 22nd 2006, at Schloss Birlinghoven, Sankt Augustin, Germany}, address = {Sankt Augustin}, pages = {112 -- 121}, language = {en} } @incollection{StrehlauKuehhorn, author = {Strehlau, Ulrik and K{\"u}hhorn, Arnold}, title = {Experimental and numerical investigations of HPC blisks with a focus on travelling waves}, series = {Proceedings of the ASME Turbo Expo 2010, presented at the 2010 ASME Turbo Expo, June 14 - 18, 2010, Glasgow, UK, Volume 6, part B}, booktitle = {Proceedings of the ASME Turbo Expo 2010, presented at the 2010 ASME Turbo Expo, June 14 - 18, 2010, Glasgow, UK, Volume 6, part B}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4401-4}, pages = {865 -- 878}, language = {en} } @misc{MaywaldBeirowKuehhorn, author = {Maywald, Thomas and Beirow, Bernd and K{\"u}hhorn, Arnold}, title = {Mistuning und D{\"a}mpfung von Radialturbinenr{\"a}dern}, series = {MTZ - Motortechnische Zeitschrift}, volume = {76}, journal = {MTZ - Motortechnische Zeitschrift}, number = {06}, issn = {2192-8843}, doi = {10.1007/s35146-015-0043-7}, pages = {68 -- 75}, abstract = {Moderne Verbrennungskraftmaschinen m{\"u}ssen ein stetig wachsendes Anforderungsprofil in Bezug auf Wirtschaftlichkeit, Leistung und Umweltfreundlichkeit erf{\"u}llen. In diesem Zusammenhang hat die Turboaufladung von Verbrennungsmotoren an Bedeutung gewonnen. Bei Turboladern kleiner und mittlerer Baugr{\"o}ße, deren Turbinen einen Durchmesser zwischen 30 und 250 mm aufweisen, kommen vornehmlich gegossene Laufr{\"a}der zum Einsatz. Am Institut f{\"u}r Verkehrstechnik der Brandenburgischen Technischen Universit{\"a}t Cottbus-Senftenberg wurde im Rahmen eines FVV-Forschungsvorhabens der Einfluss charakteristischer Betriebsgr{\"o}ßen eines Turboladers auf das strukturdynamische Verhalten solcher Radialturbinenr{\"a}der untersucht.}, language = {de} } @misc{BeirowKuehhornWeberetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Weber, Robby and Popig, Frederik}, title = {Vibration Analyses of an Axial Turbine Wheel With Intentional Mistuning}, series = {Turbo Expo 2020, Virtual Conference, Virtual Conference and Exhibition, Online, September 21 - 25, 2020}, journal = {Turbo Expo 2020, Virtual Conference, Virtual Conference and Exhibition, Online, September 21 - 25, 2020}, abstract = {The last stage bladed disk of a steam turbine is analyzed with respect to both flutter susceptibility and limitation of forced response. Due to the lack of variable stator vanes unfavorable flow conditions may occur which can lead to flow separation in some circumstances. Consequently, there is the risk of flutter in principle, particularly at nominal speed under part load conditions. For this reason, intentional mistuning is employed by the manufacturer with the objective to prevent any self-excited vibrations. A first step in this direction is done by choosing alternate mistuning, which keeps the manufactural efforts in limits since only two different blade designs are allowed. In this sense, two different series of blades have been made. However, it is well known that small deviations from the design intention are unavoidable due to the manufacturing procedure, which could be proved by bonk tests carried out earlier. The influence of these additional but unwanted deviations is considered in numerical simulations. Moreover, the strong dependence of blade frequencies on the speed is taken into account since it significantly attenuates the blade to blade frequency difference in this particular case. Within an academic study the turbine wheel is modelled as blade integrated disk in order to demonstrate fundamental effects of intentional mistuning on flutter susceptibility and forced response. For that purpose, reduced order models are built up by using the subset of nominal system mode approach introduced by Yang and Griffin [1], which conveniently allows for taking into account both differing mistuning patterns and the impact of aeroelastic interaction. Focusing on the first flap mode it could be shown that a mitigation of flutter susceptibility is achieved by prescribing alternate mistuning, which indeed affects an increase of originally small aerodynamic damping ratios. Nevertheless, the occurrence of negative damping ratios could not be completely precluded at part load conditions. That is why optimization studies are conducted based on genetic algorithms with the objective function of maximizing the lowest aerodynamic damping ratios. Again only two different blade designs are admitted. Finally, mistuning patterns could be identified causing a tremendous increase of aerodynamic damping ratios. The robustness of the solutions found could be proved by superimposing additional random mistuning. Another study is focused on the impact of mistuning strength. Further analyses are addressing the forced response at part speed conditions, where different resonance crossings are becoming apparent in the Campbell plot. An increase of the forced response compared to the tuned counterpart is partly unpreventable because of unfavorable aerodynamic damping curves. Independently, the maximum forced response has to be limited also in case of applying large intentional mistuning. [1] Yang, M. T., Griffin, J. H., „A Reduced-Order model of Mistuning Using a Subset of Nominal System Modes". J Eng Gas Turb Power, 123, pp. 893-900 (2001).}, language = {en} } @misc{FigaschewskyKuehhornBeirowetal., author = {Figaschewsky, Felix and K{\"u}hhorn, Arnold and Beirow, Bernd and Giersch, Thomas and Schrape, Sven}, title = {Analysis of mistuned forced response in an axial high-pressure compressor rig with focus on Tyler-Sofrin modes}, series = {The Aeronautical Journal}, journal = {The Aeronautical Journal}, number = {123}, issn = {2059-6464}, doi = {10.1017/aer.2018.163}, pages = {356 -- 377}, abstract = {This paper aims at contributing to a better understanding of the effect of Tyler-Sofrin Modes (TSMs) on forced vibration responses by analysing a 4.5-stage research axial compressor rig. The first part starts with a brief review of the involved physical mechanisms and necessary prerequisites for the generation of TSMs in multistage engines. This review is supported by unsteady CFD simulations of a quasi 2D section of the studied engine. It is shown that the amplitude increasing effect due to mistuning can be further amplified by the presence of TSMs. Furthermore, the sensitivity with respect to the structural coupling of the blades and the damping as well as the shape of the expected envelope is analysed. The second part deals with the Rotor 2 blisk of the research compressor rig. The resonance of a higher blade mode with the engine order of the upstream stator is studied in two different flow conditions realised by different variable stator vane (VSV) schedules which allows to separate the influence of TSMs from the impact of mistuning. A subset of nominal system modes representation of the rotor is used to describe its mistuned vibration behaviour, and unsteady CFD simulations are used to characterise the present strength of the TSMs in the particular operating conditions. Measured maximum amplitude vs blade pattern and frequency response functions are compared against the predictions of the aeromechanical models in order to assess the strength of the TSMs as well as its influence on vibration levels.}, language = {en} } @misc{BeirowKuehhornFigaschewskyetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Figaschewsky, Felix and H{\"o}nisch, Peter and Giersch, Thomas and Schrape, Sven}, title = {Model update and validation of a mistuned high-pressure compressor blisk}, series = {The Aeronautical Journal}, volume = {123}, journal = {The Aeronautical Journal}, number = {1260}, issn = {2059-6464}, doi = {10.1017/aer.2018.149}, pages = {230 -- 247}, abstract = {In order to prepare an advanced 4-stage high-pressure compressor rig test campaign, details regarding both accomplishment and analysis of preliminary experiments are provided in this paper. The superior objective of the research project is to contribute to a reliable but simultaneously less conservative design of future high pressure blade integrated disks (blisk). It is planned to achieve trend-setting advances based on a close combination of both numerical and experimental analyses. The analyses are focused on the second rotor of this research compressor, which is the only one being manufactured as blisk. The comprehensive test program is addressing both surge and forced response analyses e.g. caused by low engine order excitation. Among others the interaction of aeroelastics and blade mistuning is demanding attention in this regard. That is why structural models are needed, allowing for an accurate forced response prediction close to reality. Furthermore, these models are required to support the assessment of blade tip timing (BTT) data gathered in the rig tests and strain gauge (s/g) data as well. To gain the maximum information regarding the correlation between BTT data, s/g-data and pressure gauge data, every blade of the second stage rotor (28 blades) is applied with s/g. However, it is well known that s/g on blades can contribute additional mistuning that had to be considered upon updating structural models. Due to the relevance of mistuning, efforts are made for its accurate experimental determination. Blade-by-blade impact tests according to a patented approach are used for this purpose. From the research point of view, it is most interesting to determine both the effect s/g-instrumentation and assembling the compressor stages on blade frequency mistuning. That is why experimental mistuning tests carried out immediately after manufacturing the blisk are repeated twice, namely, after s/g instrumentation and after assembling. To complete the pre-test program, the pure mechanical damping and modal damping ratios dependent on the ambient pressure are experimentally determined inside a pressure vessel. Subsequently the mistuning data gained before is used for updating subset of nominal system mode (SNM) models. Aerodynamic influence coefficients (AICs) are implemented to take aeroelastic interaction into account for forced response analyses. Within a comparison of different models, it is shown for the fundamental flap mode (1F) that the s/g instrumentation significantly affects the forced response, whereas the impact of assembling the compressor plays a minor role.}, language = {en} } @misc{HenkeNoackGeyeretal., author = {Henke, Anna-Sophia and Noack, Martin and Geyer, Thomas and Heinrich, Christoph Rocky and Beirow, Bernd and Sarradj, Ennes and K{\"u}hhorn, Arnold}, title = {Calculation of the Modal Behavior of Structured Sheet Metal}, series = {International Journal of Lightweight Materials and Manufacture}, journal = {International Journal of Lightweight Materials and Manufacture}, issn = {2588-8404}, doi = {10.1016/j.ijlmm.2019.01.004}, pages = {13}, language = {en} } @misc{NaveedKuehhornKober, author = {Naveed, Zishan and K{\"u}hhorn, Arnold and Kober, Markus}, title = {Contact Behaviour of Isogeometric Analysis for Rotating Structures and its Industrial Application by Coupling to the Classical Finite Element Method}, series = {VII International Conference on Isogeometric Analysis, M{\"u}nchen, 18.-20. September 2019}, journal = {VII International Conference on Isogeometric Analysis, M{\"u}nchen, 18.-20. September 2019}, pages = {1}, abstract = {Especially for rotating structures like bearings non-smooth contact surfaces, as they appear in classical finite element modeling, lead to various problems during the analysis involving mesh interlocking and spurious oscillations in contact forces. In order to eliminate these issues, very fine meshes and additional smoothing strategies are employed in case of the finite element method (FEM). But also Non-Uniform Rational B-splines (NURBS) based isogeometric analysis (IGA) can be very useful for the contact analysis due to the inherent higher order continuity of NURBS basis functions. In this contribution, the contact behavior using classical FEA and IGA approaches is studied by means of an example of a pendulum under gravitational load. In addition, a more practical example of a coupled IGA-FEM problem with a cylindrical roller bearing is also reported in this paper. This research study of contact analysis has been carried out for the above mentioned examples using LS-DYNA and illustrates that contact surfaces of coarsely meshed geometry lock the rotation of the parts in case of classical FEM. On the contrary, when the contact surface is represented by NURBS elements it allows the rotation of the parts and effectively alleviates the contact force oscillation.}, language = {en} } @inproceedings{BeirowKuehhornGolze, author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Golze, Mark}, title = {Experimental and Numerical Investigations of High pressure Compressor Blades Vibration Behavior Considering Mistuning}, language = {en} } @misc{MaywaldHeinrichKuehhornetal., author = {Maywald, Thomas and Heinrich, Christoph Rocky and K{\"u}hhorn, Arnold and Schrape, Sven and Backhaus, Thomas}, title = {Prediction of Geometrically Induced Localization Effects Using a Subset of Nominal System Modes}, series = {ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition June 17-21, 2019 Phoenix, Arizona, USA}, journal = {ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition June 17-21, 2019 Phoenix, Arizona, USA}, isbn = {978-0-7918-5869-1}, doi = {10.1115/GT2019-90884}, pages = {9}, abstract = {It is widely known that the vibration characteristics of blade integrated discs can dramatically change in the presence of manufacturing tolerances and wear. In this context, an increasing number of publications discuss the influence of the geometrical variability of blades on phenomena like frequency splitting and mode localization. This contribution is investigating the validity of a stiffness modified reduced order model for predicting the modal parameters of a geometrically mistuned compressor stage. In detail, the natural frequencies and mode shapes, as well as the corresponding mistuning patterns, are experimentally determined for an exemplary rotor. Furthermore, a blue light fringe projector is used to identify the geometrical differences between the actual rotor and the nominal blisk design. With the help of these digitization results, a realistic finite element model of the whole compressor stage is generated. Beyond that, a reduced order model is implemented based on the nominal design intention. Finally, the numerical predictions of the geometrically updated finite element model and the stiffness modified reduced order model are compared to the vibration measurement results. The investigation is completed by pointing out the benefits and limitations of the SNM-approach in the context of geometrically induced mistuning effects.}, language = {en} } @misc{FigaschewskyKuehhornBeirowetal., author = {Figaschewsky, Felix and K{\"u}hhorn, Arnold and Beirow, Bernd and Giersch, Thomas and Schrape, Sven and Nipkau, Jens}, title = {An inverse approach to identify tuned aerodynamic damping, system frequencies and mistuning - Part 3: Application to engine data}, series = {ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition, June 17-21, 2019, Phoenix, Arizona, USA}, journal = {ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition, June 17-21, 2019, Phoenix, Arizona, USA}, isbn = {978-0-7918-5868-4}, doi = {10.1115/GT2019-91337}, pages = {13}, abstract = {A novel approach for the identification of tuned aerodynamic damping, system frequencies, forcing and mistuning has been introduced in the first part of this paper. It is based on the forced response equations of motion for a blade dominated mode family. A least squares formulation allows to identify the system's parameters directly from measured frequency response functions (FRFs) of all blades recorded during a sweep through a resonance. The second part has dealt with its modification and application to experimental modal analyses of blisks at rest. This 3rd part aims at presenting the application of the approach to blade tip timing (BTT) data acquired in rig tests. Therefore, blisk rotors of two different engines are studied: a single stage fan rig and a 4.5 stage high pressure compressor (HPC) rig. The rig test campaign of the fan blisk included also an intentional mistuning experiment that allows to study the performance of the identification approach for a similar rotor with two different mistuning levels. It is demonstrated that the approach can identify aerodynamic damping curves, system frequencies, mistuning pattern and forced travelling wave modes (TWMs) from state of the art BTT data monitored during rig or engine tests. All derived mistuning patterns could be verified with reference measurements at standstill. The derived aerodynamic damping curves and system frequencies show a reasonable agreement with simulations. For the HPC case a multitude of excited TWMs could be identified which also lines up with previous simulations.}, language = {en} } @misc{BeirowKuehhornFigaschewskyetal., author = {Beirow, Bernd and K{\"u}hhorn, Arnold and Figaschewsky, Felix and Bornholm, Alfons}, title = {Vibration analysis of a mistuned axial turbine blisk}, series = {ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition, June 17-21, 2019, Phoenix, Arizona, USA}, journal = {ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition, June 17-21, 2019, Phoenix, Arizona, USA}, isbn = {978-0-7918-5869-1}, doi = {10.1115/GT2019-92047}, pages = {12}, abstract = {An axial turbine blisk for turbocharger applications is analyzed with respect to the effect of intentional mistuning on the forced response. Originally, the intentional mistuning pattern has been designed by employing a genetic algorithm optimization in order to reduce the forced response caused by low engine order excitation (LEO) of the fundamental flap mode. The solution found has been implemented in a prototype of that blisk. For the purpose of comparison, a second reference blisk has been manufactured without intentional mistuning. The actual mistuning distributions of the blisks have been identified by employing blade-by-blade impact testing. Alternatively, a new inverse approach has been employed, which is based on a least squares formulation and benefits from less experimental effort. Based on the information gained by the aforementioned testing procedures, subset of nominal systems (SNM)-models have been updated, which allow for considering the aeroelastic coupling by means of aerodynamic influence coefficients (AIC). Despite of small but unavoidable deviations from the design intention it could be proved within numerical simulations that the intended 70 per cent reduction of the maximum forced response is nevertheless achieved. In addition, the paper is addressing the effect of the aforementioned intentional mistuning pattern on a higher mode, which is relevant for the durability as well. Hence, new SNM-models have to be updated in order to calculate the forced response due to EO-excitation caused by the nozzle guide vane. Although the original mistuning pattern has been optimized solely for reducing the forced response of the fundamental flap mode, it hardly affects the higher mode forced response in a negative manner.}, language = {en} } @misc{KoberKuehhornKeskin, author = {Kober, Markus and K{\"u}hhorn, Arnold and Keskin, Akin}, title = {Instabilit{\"a}tsprobleme bei der impliziten transienten FEM-Simulation schnell rotierender elastischer Strukturen - Beschreibung des Ph{\"a}nomens und L{\"o}sungsm{\"o}glichkeiten}, series = {NAFEMS-Online-Magazin}, volume = {48}, journal = {NAFEMS-Online-Magazin}, number = {4}, issn = {2311-522X}, pages = {36 -- 49}, language = {en} } @misc{NaveedKuehhornKober, author = {Naveed, Zishan and K{\"u}hhorn, Arnold and Kober, Markus}, title = {Comparative Evaluation of Isogeometric Analysis and Classical FEM with Regard to Contact Anaylsis}, series = {12th European LS-DYNA Conference 2019, 14-16 May 2019, Koblenz}, journal = {12th European LS-DYNA Conference 2019, 14-16 May 2019, Koblenz}, pages = {10}, abstract = {Isogeometric analysis represents a newly developed technique that offers the application of Computer Aided Designs (CAD) concept of Non-uniform Rational B-Splines (NURBS) tool to describe the geometry of the computational domain. The simplified transition of CAD models into the computational domain eliminates the problems arising from the geometrical discontinuities induced by the faceted approximation of the mesh. Moreover, numerical analysis directly on NURBS objects significantly reduces the design-to-analysis time compared to traditional FEA approach. In the field of contact mechanics, when finite elements are applied to geometry with curved surfaces, the result is a non-smooth geometrical representation of interface surfaces which may lead to mesh interlocking, high jumps and spurious oscillations in contact forces. To eliminate these issues, various surface smoothening strategies are to be employed in case of FEM. Isogeometric based analysis alleviates these issues without employing any additional smoothening strategy due to inherent higher order continuity of NURBS basis functions and much more accurate results are obtained compared to conventional FE approach. In the current study, LS-DYNA is used to demonstrate the capabilities and advantage of an isogeometric analysis though an example of pendulum under gravitational load. The numerical simulation results are analytically validated and the comparison of NURBS surfaces with faceted surfaces is carried out to investigate the accuracy.}, language = {en} } @misc{WeberKuehhornBeirow, author = {Weber, Robby and K{\"u}hhorn, Arnold and Beirow, Bernd}, title = {Mistuning and Damping of Turbine and Compressor Impellers}, series = {MTZ worldwide}, volume = {80}, journal = {MTZ worldwide}, number = {9}, issn = {2192-9114}, doi = {10.1007/s38313-019-0090-4}, pages = {72 -- 77}, abstract = {Turbocharging is known to be a well-established technology for an engine's efficiency and power output by forcing extra compressed air into the combustion chamber. The centrifugal loads, necessary flow deflections, unsteady pressure fluctuations, and structural temperature gradients put a high strain on rotating components. Additionally, those components are prone to high-cycle fatigue. The Chair of Structural Mechanics and Vehicle Vibrational Technology at the BTU Cottbus-Senftenberg investigated the impact of manufacturing tolerances on the vibrational behavior of several turbine and compressor impellers. Finally, it is shown that intentional mistuning can lead to significantly lower stresses.}, language = {en} } @article{SchrapeKuehhorn, author = {Schrape, S. and K{\"u}hhorn, Arnold}, title = {FSI of a Simplified Aero Engine Compressor Cascade Configuration}, series = {Proceedings in applied mathematics and mechanics : PAMM}, volume = {6}, journal = {Proceedings in applied mathematics and mechanics : PAMM}, number = {1}, issn = {1617-7061}, pages = {457 -- 458}, language = {en} } @article{KuehhornGolze, author = {K{\"u}hhorn, Arnold and Golze, Mark}, title = {Thickness flexible sandwich theory for the common description of global and local effects}, language = {en} } @article{SchrodtBenderothKuehhorn, author = {Schrodt, M. and Benderoth, G. and K{\"u}hhorn, Arnold}, title = {Hyperelastic description of Polymer Soft Foams at Finite Deformations}, language = {en} } @misc{FigaschewskyBeirowKuehhornetal., author = {Figaschewsky, Felix and Beirow, Bernd and K{\"u}hhorn, Arnold and Nipkau, Jens and Giersch, Thomas and Powers, Bronwyn}, title = {Design and Analysis of an Intentional Mistuning Experiment Reducing Flutter Susceptibility and Minimizing Forced Response of a Jet Engine Fan}, series = {ASME Turbo Expo 2017, GT2017-64621, June 26-30, 2017, Charlotte, NC, USA, Volume 7B}, journal = {ASME Turbo Expo 2017, GT2017-64621, June 26-30, 2017, Charlotte, NC, USA, Volume 7B}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5093-0}, doi = {10.1115/GT2017-64621}, pages = {13}, abstract = {Recent demands for a reduction of specific fuel consumption of jet engines have been opposed by increasing propulsive efficiency with higher bypass ratios and increased engine sizes. At the same time the challenge for the engine development is to design safe and efficient fan blades of high aspect ratios. Since the fan is the very first rotor stage, it experiences significant distortions in the incoming flow depending on the operating conditions. Flow distortions do not only lead to a performance and stall margin loss but also to remarkable low engine order (LEO) excitation responsible for forced vibrations of fundamental modes. Additionally, fans of jet engines typically suffer from stall flutter, which can be additionally amplified by reflections of acoustic pressure waves at the intake. Stall flutter appears before approaching the stall line on the fan's characteristic and limits its stable operating range. Despite the fact that this "flutter bite" usually affects only a very narrow speed range, it reduces the overall margin of safe operation significantly. With increasing aspect ratios of ultra-high bypass ratio jet engines the flutter susceptibility will probably increase further and emphasizes the importance of considering aeromechanical analyses early in the design phase of future fans. This paper aims at proving that intentional mistuning is able to remove the flutter bite of modern jet engine fans without raising issues due to heavily increased forced vibrations induced by LEO excitation. Whereas intentional mistuning is an established technology in mitigating flutter, it is also known to amplify the forced response. However, recent investigations considering aeroelastic coupling revealed that under specific circumstances mistuning can also reduce the forced response due to engine order excitation. In order to allow a direct comparison and to limit costs as well as effort at the same time, the intentional mistuning is introduced in a non-destructive way by applying heavy paint to the blades. Its impact on the blade's natural frequencies is estimated via finite element models with an additional paint layer. In parallel, this procedure is experimentally verified with painted fan blades in the laboratory. A validated SNM (subset of nominal system modes) representation of the fan is used as a computational model to characterize its mistuned vibration behavior. Its validation is done by comparing mistuned mode shape envelopes and frequencies of an experimental modal analysis at rest with those obtained by the updated computational model. In order to find a mistuning pattern minimizing the forced response of mode 1 and 2 at the same time and satisfying stability and imbalance constraints, a multi-objective optimization has been carried out. Finally, the beneficial properties of the optimized mistuning pattern are verified in a rig test of the painted rotor. Copyright © 2017 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @misc{HanschkeKlaukeKuehhorn, author = {Hanschke, Benjamin and Klauke, Thomas and K{\"u}hhorn, Arnold}, title = {The Effect of Foreign Object Damage on Compressor Blade High Cycle Fatigue Strength}, series = {ASME Turbo Expo 2017, GT2017-63559, June 26-30, 2017, Charlotte, NC, USA, Volume 7A}, journal = {ASME Turbo Expo 2017, GT2017-63559, June 26-30, 2017, Charlotte, NC, USA, Volume 7A}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5092-3}, doi = {10.1115/GT2017-63599}, pages = {9}, abstract = {For a considerable amount of time blade integrated disks (blisks) are established as a standard component of high pressure compressors (HPCs) in aero engines. Due to the steady requirement to increase the efficiency of modern HPCs, blade profiles get thinned out and aerodynamic stage loading increases. Ever since, aerofoil design has to balance structural and aerodynamic requirements. One particularity of aero engines is the possibility to ingest different kinds of debris during operation and some of those particles are hard enough to seriously damage the aerofoil. Lately, a growing number of blisk-equipped aero engines entered service and the question of foreign object damage (FOD) sensitivity relating to compressor blade high cycle fatigue (HCF) has emerged. Correct prediction of fatigue strength drop due to a FOD provides a huge chance for cost cutting in the service sector as on-wing repairs (e.g. borescope blending) are much more convenient than the replacement of whole blisks and corresponding engine strips. The aim of this paper is to identify critical FOD-areas of a modern HPC stage and to analyze the effects of stress concentrations — caused by FOD — on the fatigue strength. A process chain has been developed, that automatically creates damaged geometries, meshes the parts and analyses the fatigue strength. Amplitude frequency strength (af-strength) has been chosen as fatigue strength indicator owing to the fact, that amplitudes and frequencies of blade vibrations are commonly measured either by blade tip timing or strain gauges. Furthermore, static and dynamic stress concentrations in damaged geometries compared to the reference design were computed. A random variation of input parameters was performed, such as the radial damage position at blade leading edge and damage diameter. Based on results of the different samples, correlations of input parameters and the fatigue strength drop have been investigated. Evaluation shows a significant mode dependence of critical blade areas with a large scatter between drops in fatigue strength visible for mode to mode comparison. Keeping in mind the necessity of fast response times in the in-service sector, FOD sensitivity computations could be performed for all blade rows of the HPC — including the analysis of possible borescope blending geometries — in the design stage. Finally, the actual amplitude frequency levels (af-levels) of the modes excited during operation have to be appropriately taken into consideration. For example, a pronounced af-strength drop due to a FOD may not be critical for safe engine operations because the observed mode is excited by small af-levels during operation. Hence, the endurance ratio — a quotient of af-level and af-strength — is used as assessment criterion. Copyright © 2017 by ASME}, language = {en} } @misc{MaywaldBackhausSchrapeetal., author = {Maywald, Thomas and Backhaus, Thomas and Schrape, Sven and K{\"u}hhorn, Arnold}, title = {Geometric Model Update of Blisks and its Experimental Validation for a Wide Frequency Range}, series = {ASME Turbo Expo 2017, GT2017-63446, June 26-30, 2017, Charlotte, NC, USA, Volume 7A}, journal = {ASME Turbo Expo 2017, GT2017-63446, June 26-30, 2017, Charlotte, NC, USA, Volume 7A}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5092-3}, doi = {10.1115/GT2017-63446}, pages = {9}, abstract = {The contribution discusses a model update procedure and its experimental validation in the context of blisk mistuning. Object of investigation is an industrial test blisk of an axial compressor which is milled from solid using a state of the art 5-axis milling machine. First, the blisk geometry is digitized by a blue light fringe projector. Digitization is largely automated using an industrial robot cell in order to guarantee high repeatability of the measurement results. Additionally, frequency mistuning patterns are identified based on vibration measurements. Here, the system excitation is realized by a modal impact hammer. The blade response is detected using a laser scanning vibrometer. Furthermore, all blades except the currently excited one are detuned with additional masses. Applying these masses allows to identify a blade dominated natural frequency for each blade and every mode of interest. Finally, these blade dominated frequencies are summarized to mode specific mistuning patterns. The key part of the contribution presents a model update approach which is focused on small geometric deviations between real engine parts and idealized simulation models. Within this update procedure the nodal coordinates of an initially tuned finite element blisk model were modified in order to match the geometry of the real part measured by blue light fringe projection. All essential pre- and post-processing steps of the mesh morphing procedure are described and illustrated. It could be proven that locally remaining geometric deviations between updated finite element model and the optical measurement results are below 5 μm. For the purpose of validation blade dominated natural frequencies of the updated finite element blisk model are calculated for each sector up to a frequency of 17 kHz. Finally, the numerically predicted mistuning patterns are compared against the experimentally identified counterparts. At this point a very good agreement between experimentally identified and numerically predicted mistuning patterns can be proven across several mode families. Even mistuning patterns of higher modes at about 17 kHz are well predicted by the geometrically mistuned finite element model. Within the last section of the paper, possible uncertainties of the presented model update procedure are analyzed. As a part of the study the digitization of the investigated blisk has been repeated for ten times. These measurement results serve as input for the model update procedure described before. In the context of this investigation ten independent geometrical mistuned simulation models are created and the corresponding mistuning patterns are calculated. Copyright © 2017 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @misc{KrauseStelldingerHanschkeetal., author = {Krause, Christoph and Stelldinger, Marco and Hanschke, Benjamin and K{\"u}hhorn, Arnold and Giersch, Thomas}, title = {Asynchronous Response Analysis of Non-Contact Vibration Measurements on Compressor Rotor Blades}, series = {ASME Turbo Expo 2017, GT2017-63200, June 26-30, 2017, Charlotte, NC, USA, Volume 7B}, journal = {ASME Turbo Expo 2017, GT2017-63200, June 26-30, 2017, Charlotte, NC, USA, Volume 7B}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5093-0}, doi = {10.1115/GT2017-63200}, abstract = {Although the research in non-intrusive techniques for the measurement of vibration have made major progress since the beginning in the 1960's, they are still mainly used as additional tool to the common strain gauges. Therefore, there is still a great deal of interest in the improvement of such non-contact vibration measurement techniques, to replace the intrusive ones with alternative techniques. One possibility to monitor all blades at once is blade tip-timing. The probes for a blade tip-timing measurement system are mounted circumferentially in the engine casing to log the passing times of the rotor blades. These logged time data will be compared with theoretically calculated passing times. The deviation between measured and calculated passing times can be transformed to blade displacement values. In recent years, several methods to analyse the acquired vibration data have been developed and improved. They are directed to evaluate synchronous and asynchronous blade vibration events. This paper focuses on the identification of asynchronous vibrations on rotor blades using blade tip-timing. Taking the data from all probes into account gives an opportunity to determine the vibration of each single blade. Due to the usage of a research test rig, all measurement data could be acquired in simulated real case operation scenarios. Analysis data were evaluated with a developed post processing routine based on a Fourier transformation algorithm coupled with a least square fitting procedure. Since compressor surge represents one of the most critical non synchronous events during compressor operation, in this paper a special interest is paid to the analysis of compressor surges. Vibration frequencies revealed during surge investigation will be compared with simultaneously measured strain gauge data to ensure the reliability of blade tip-timing measurement and analysis. To explain the results in more detail, the possibility of a blade damaged triggered shift of the blade characteristic frequency is shown. The most promising result of the analysis is the close correlation between the identified vibration frequencies of compressor surge events and the afterwards determined frequency mistuning and crack distributions. Blade damage becomes visible through increasing deviation between characteristic frequencies of different blades as result of multiple surge events. In addition, with the comparison of mean frequency records over each single surge among each other it is possible to restrict the blade damage time. Subsequently, the possibility to develop a process routine to predict blade damage during compressor test series could arise.}, language = {en} } @misc{BeirowFigaschewskyKuehhornetal., author = {Beirow, Bernd and Figaschewsky, Felix and K{\"u}hhorn, Arnold and Bornholm, Alfons}, title = {Modal Analyses of an Axial Turbine Blisk With Intentional Mistuning}, series = {ASME Turbo Expo 2017, GT2017-63193, June 26-30, 2017, Charlotte, NC, USA, Volume 7B}, journal = {ASME Turbo Expo 2017, GT2017-63193, June 26-30, 2017, Charlotte, NC, USA, Volume 7B}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-5093-0}, doi = {10.1115/GT2017-63193}, pages = {10}, abstract = {The potential of intentional mistuning to reduce the maximum forced response is analyzed within the development of an axial turbine blisk for ship diesel engine turbocharger applications. The basic idea of the approach is to provide an increased aerodynamic damping level for particular engine order excitations and mode shapes without any significant distortions of the aerodynamic performance. The mistuning pattern intended to yield a mitigation of the forced response is derived from an optimization study applying genetic algorithms. Two blisk prototypes have been manufactured a first one with and another one without employing intentional mistuning. Hence, the differences regarding the real mistuning and other modal properties can be experimentally determined and evaluated as well. In addition, the experimental data basis allows for updating structural models which are well suited to compute the forced response under operational conditions. In this way, the real benefit achieved with the application of intentional mistuning is demonstrated. Copyright © 2017 by ASME}, language = {en} } @misc{FigaschewskyKuehhornBeirowetal., author = {Figaschewsky, Felix and K{\"u}hhorn, Arnold and Beirow, Bernd and Giersch, Thomas and Nipkau, Jens and Meinl, Ferdinand}, title = {Simplified Estimation of Aerodynamic Damping for Bladed Rotors, Part 2: Experimental Validation During operation}, series = {ASME Turbo Expo 2016, Turbomachinery Technical Conference and Exposition, Volume 7B, Structures and Dynamics, Seoul, South Korea, June 13-17, 2016}, journal = {ASME Turbo Expo 2016, Turbomachinery Technical Conference and Exposition, Volume 7B, Structures and Dynamics, Seoul, South Korea, June 13-17, 2016}, publisher = {ASME}, address = {New York, NY [u.a.]}, isbn = {978-0-7918-4984-2}, doi = {10.1115/GT2016-56458}, abstract = {Due to increasing requirements of future engine projects, much effort has been spent on the design of more efficient turbomachinery blades in the recent years. Besides aerodynamic efficiency constraints, these designs need to meet structural criteria ensuring that they are safe and robust with respect to High Cycle Fatigue (HCF). The estimation of the resonant vibration amplitude is done based on the aerodynamic force and the overall damping level. Since, for many applications the contribution of mechanical damping is often rather low compared to the aerodynamic counterpart, the determination of the aerodynamic damping is vital for the estimation of the forced vibration response. This second part is meant to contribute to a simplified computation of the aerodynamic damping during operation by making additional assumptions: The investigated mode family shall not suffer from flutter, has a high reduced frequency and the influence of adjacent blades is negligible. Under these circumstances a simplified approach can be introduced that allows for the computation of the mean value of the aerodynamic damping based on a steady state CFD solution of the regarded stage. It is well known, that the aerodynamic damping of a blade mode family depends on the inter blade phase angle (IBPA) and its direction of propagation, which is not covered by the simplified approach. For higher modes the difference between the minimum and maximum damping is often low and the mean value is a good approximation, whereas for fundamental modes there is often a significant difference. However, it is shown that considering a mistuned vibration response of the rotor, the expected value of the mistuned damping exhibits the mean value of IBPA-dependent aerodynamic damping. CFD simulations of an oscillating airfoil indicate a certain validity range of the simplified approach based on a modified reduced frequency and inlet Mach number, which allows to determine for which industrial applications the approach is most suitable. Finally, this range of validity is verified with experimentally determined overall damping values from strain gauge measurements during operation for 2 different industrial applications, an axial compressor stage of a jet engine and a radial turbine stage of a turbocharger. Copyright © 2016 by Rolls-Royce Deutschland Ltd \& Co KG}, language = {en} } @misc{WagnerKuehhornWeissetal., author = {Wagner, Frank and K{\"u}hhorn, Arnold and Weiss, Thomas and Otto, Dierk}, title = {Influence of different parametrizations on the optimum design of a high pressure turbine blade firtree}, series = {ASME Turbo Expo 2016, Turbomachinery Technical Conference and Exposition, Volume 7A, Structures and Dynamics, Seoul, South Korea, June 13-17, 2016}, journal = {ASME Turbo Expo 2016, Turbomachinery Technical Conference and Exposition, Volume 7A, Structures and Dynamics, Seoul, South Korea, June 13-17, 2016}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4983-5}, doi = {10.1115/GT2016-56749}, pages = {11}, abstract = {Today the design processes in the aero industry face many challenges. Apart from automation itself, a suitable parametric geometry setup plays a significant role in making workflows usable for optimization. At the same time there are tough requirements against the parametric model. For the lowest number of possible parameters, which should be intuitively ascertainable, a high flexibility has to be ensured. Within the parameter range an acceptable stability is necessary. Under these constraints the creation of such parametric models is a challenge, which should not be underestimated especially for a complex geometry. In this work different kinds of parametrization with different levels of complexity will be introduced and compared. Thereby several geometry elements will be used to handle the critical regions of the geometry. In the simplest case a combination of lines and arcs will be applied. These will be replaced by superior elements like a double arc construct or different formulations of b-splines. There will be an additional focus on the variation of spline degree and control points. To guarantee consistency a set of general parameters will be used next to the specific ones at the critical regions. The different parameter boundaries have a influence on the possible geometries and should therefore be tested separately before an optimization run.}, language = {en} } @misc{BeirowMaywaldFigaschewskyetal., author = {Beirow, Bernd and Maywald, Thomas and Figaschewsky, Felix and K{\"u}hhorn, Arnold and Heinrich, Christoph Rocky and Giersch, Thomas}, title = {Simplified Determination of Aerodynamic Damping for Bladed Rotors, Part 1: Experimental Validation at Rest}, series = {ASME Turbo Expo 2016, Turbomachinery Technical Conference and Exposition, Volume 7B, Structures and Dynamics, Seoul, South Korea, June 13-17, 2016}, journal = {ASME Turbo Expo 2016, Turbomachinery Technical Conference and Exposition, Volume 7B, Structures and Dynamics, Seoul, South Korea, June 13-17, 2016}, publisher = {ASME}, address = {New York, NY}, isbn = {978-0-7918-4984-2}, doi = {10.1115/GT2016-56535}, abstract = {Considering both a radial turbine rotor of a turbocharger and an axial compressor test blisk at rest, aerodynamic damping characteristics are experimentally and numerically analyzed. Linear dependencies of modal damping ratios on the ambient pressure or the acoustic impedance, respectively, could be shown within experiments carried out inside a pressure chamber. The impact of the ambient air clearly dominates the modal damping ratios compared to the minor contribution of the structure. Assuming that acoustic emission can be regarded as main source of aerodynamic damping a simplified approach for its determination is introduced which only depends on natural frequency, mode shape and acoustic impedance. It is shown that a satisfying match between experiment and computation is achieved for those cases which are dedicated to sufficiently small ratios between wave lengths of acoustic emissions and blade distances.}, language = {en} }