@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{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{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} } @phdthesis{Weber, author = {Weber, Robby}, title = {Ein Beitrag zur schwingungssicheren Auslegung von radialen Turbomaschinen mit Fokus auf Mistuning und D{\"a}mpfung}, publisher = {Mensch und Buch Verlag}, address = {Berlin}, isbn = {978-3-86387-986-0}, pages = {174}, abstract = {Radiale Turbinen- und Verdichterr{\"a}der bilden hinsichtlich Wirtschaftlichkeit, Effizienz und insbesondere Umweltvertr{\"a}glichkeit essenzielle Eckpfeiler moderner Verbrennungskraftmaschinen. Sie repr{\"a}sentieren in vielf{\"a}ltigen technischen Anwendungen den Stand der Technik. Umweltrelevante Aspekte beeinflussen die Entwicklung der Verbrennungsmotoren und treiben somit die Entwicklung der Abgasaufladung voran. Im Allgemeinen sind hierf{\"u}r besonders hohe Druckverh{\"a}ltnisse erforderlich, die die Struktur erheblich belasten. Die hohen aerodynamischen Anspr{\"u}che erfordern filigrane Schaufelgeometrien. Immer d{\"u}nnere Schaufeln, in Verbindung mit der geringen mechanischen D{\"a}mpfung infolge der Integralbauweise erschweren die schwingungssichere Auslegung von Turbomaschinen. Kleinste Imperfektionen, die bereits w{\"a}hrend der Fertigung entstehen, dominieren das dynamische Verhalten realer Komponenten. Die Abweichung vom urspr{\"u}nglichen Design wird als Verstimmung (engl. Mistuning) bezeichnet. Die weitgehend zuf{\"a}llige Verstimmung reduziert die Lebensdauer der Komponenten, die durch Fliehkraft, Str{\"o}mungsumlenkung, instation{\"a}re Druckschwankungen der Str{\"o}mung sowie Temperaturgradienten dauerhaft hoch belastet sind. Die vorliegende Arbeit widmet sich der Beschreibung des Strukturverhaltens radialer Laufr{\"a}der. Der Fokus der Arbeit liegt auf der Beschreibung der Radialturbine des Typs MAN TCR 18. Zus{\"a}tzlich werden die Erkenntnisse dieses Laufrades mit weiteren radialen Laufr{\"a}dern verglichen. Auf Grundlage von Messdaten, numerischen Berechnungsmodellen und Simulationsergebnissen gelingt es schließlich einen Leitfaden zur schwingungssicheren Auslegung von radialen Turbomaschinen mit dem Fokus auf Mistuning und D{\"a}mpfung bereitzustellen. Die Arbeit kommt zu dem Schluss, dass die erzwungene Schwingungsantwort mithilfe der gezielten Schaufelverstimmung signifikant gesenkt werden kann.}, language = {de} } @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} } @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} } @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} } @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} } @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{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{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} }