@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} } @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} } @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} } @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{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} } @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} } @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} } @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} } @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} } @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} } @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 = {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} } @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} }