TY - GEN A1 - Nakos, Alex A1 - Beirow, Bernd A1 - Zobel, Arthur T1 - Vibration Analyses of Radial Turbine Wheels Considering Structural and Aerodynamic Mistuning T2 - Proceedings of Global Power and Propulsion Society N2 - Radial turbine wheels of exhaust gas turbochargers are permanently exposed to centrifugal, thermal, and aerodynamic loading. However, since these wheels are commonly designed as integral structures featuring relatively little mechanical damping, they are prone to the impact of unavoidable structural random mistuning, which may evoke severe magnifications of the forced response. Nonetheless, the safe operation of turbochargers has to be ensured at any time so that the contribution of aerodynamic damping is of particular importance. Moreover, the application of intentional mistuning is known to be a suitable measure to limit or even reduce the forced response by means of increasing the resulting aerodynamic damping. In this paper, two turbine wheels of the same type are considered, one manufactured with and another one without intentional mistuning. Experimental determinations of the mistuning patterns actually reveal deviations from the design intentions, which are considered in updated numerical models. Forced response simulations demonstrate that the targeted response reduction affected by intentional mistuning is achieved anyhow. Furthermore, the general robustness of the solution is proved with respect to the maximum forced response by means of comprehensive probabilistic numerical analyses addressing the impact of additional random structural mistuning, the magnitude of intentional mistuning, and aerodynamic mistuning. Y1 - 2022 UR - https://gpps.global/gpps-chania22-proceedings/ U6 - https://doi.org/10.33737/gpps22-tc-61 SN - 2504-4400 ER - TY - GEN A1 - Kober, Markus A1 - Beirow, Bernd A1 - Singh, Kai Navtej T1 - Towards the Isogeometric Aero-Engine T2 - Proceedings of 16th German LS-DYNA Forum, 11.-12. Oktober 2022, Bamberg Y1 - 2022 UR - https://www.dynamore.it/en/training/conferences/upcoming/16th-german-ls-dyna-forum-2022/preliminary-agenda#tag-1 SN - 978-3-9816215-8-7 ER - TY - GEN A1 - Nakos, Alex A1 - Beirow, Bernd A1 - Wirsum, Manfred A1 - Schafferus, Markus A1 - Sasakaros, Marios A1 - Vogt, Damian A1 - Zobel, Arthur T1 - Mistuning and Damping of a Radial Turbine Wheel. Part 3: Validation of Intentional Mistuning During Machine Operation T2 - Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023 N2 - This contribution investigates the implementation and verification of intentional mistuning (IM) to a radial turbine wheel of an exhaust turbocharger. In principle, inaccuracies in manufacture or material inhomogeneities may lead to random blade mistuning and thus localized modes with severely magnified blade vibrations can occur. With regard to axial compressors and turbines, IM has proved to be an efficient measure to mitigate the forced response. For radial turbine wheels, on the other hand, a successful implementation of IM into a wheel hardware has not yet been presented. This work aims at the design, implementation, and verification of successful IM considering both measurements at standstill and test runs on a turbocharger test rig. The fundamental analyses have been carried out in part one [1] of this three-part paper in order to find a suitable IM-pattern featuring only two different blade designs. The AABB sequence was identified to be the most promising one in terms of mitigating the maximum forced response of the fundamental bending mode at the considered operating point. In concrete terms, a 40% attenuation of the maximum forced response was predicted by employing reduced order models. The second part [2] discussed the detailed geometric adaption of the turbine wheel hardware focussing on the implementation and validation of the IM pattern under laboratory conditions (standstill). Part three is about validating the efficacy of IM under operating conditions. In that sense, the successful implementation of IM and thus the machining of the wheel hardware are investigated within the framework of test runs on a turbocharger test rig. Test runs are conducted for both a wheel with and a wheel without IM. Non-intrusive blade-tip-timing (BTT) technology is employed to record forced response data. A well-known approach to evaluate the raw data namely times of arrival (TOA) without the availability of a once-per-revolution (OPR) signal is adapted, implemented, and applied for the evaluation. The results are compared to those received by using a commercial evaluation software for BTT measurement data. Finally, the actual gain achieved by means of IM is discussed in detail. KW - Intentional Mistuning KW - Blade Vibration KW - Damping Y1 - 2023 SN - 978-0-7918-8706-6 U6 - https://doi.org/10.1115/GT2023-101993 ER - TY - GEN A1 - Gambitta, Marco A1 - Beirow, Bernd A1 - Klauke, Thomas T1 - Investigation of Rear Blisk Drum Dynamics Under Consideration of Multi-Stage Coupling T2 - Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023 N2 - The analysis of the structural dynamics of multistage cyclic structures as linked components is required to model the interstage coupling. In turbomachinery, this can result in a collaboration between different compressor or turbine stages. This paper investigates the coupling between two rear drum blade integrated disk stages of an axial compressor to support the mechanical design process. Considering the vibration modeshapes of a multistage system, different components may co-participate in the dynamics. For this reason, a criteria to identify the modes affected by the coupling and to quantify this coupling is defined. This allows to distinguish between modes with inter-stage coupling, requiring the multistage system for their description, and uncoupled modes, involving a single stage. In addition, it is of interest to research methods to reduce the impact of the coupling on the vibrating system without drastically altering the geometry of the components. The vibration analyses of a two-stage compressor generalized geometry, representative of a compressor rear drum blisk, is presented as a study case. The use of a reducing method allows to describe the behavior of the nominal multistage system with a computationally efficient technique, enabling a parametric analysis of the stages’ coupling. The investigation considers the effect of a set of geometrical and mechanical parameters on the dynamics, identifying the driving parameters of the coupled vibration characteristics. Y1 - 2023 SN - 978-0-7918-8705-9 U6 - https://doi.org/10.1115/GT2023-103756 ER - TY - GEN A1 - Nakos, Alex A1 - Beirow, Bernd T1 - On the Influence of Installation on the Forced Response of Radial Turbine Wheels T2 - Proceedings of Global Power and Propulsion Society, GPPS Hongkong, October 16 - 19, 2023 N2 - Radial turbine wheels are commonly designed as integrally bladed rotors featuring extremely low structural damping in comparison to separate designs of blades and disk. Consequently, they are more prone to vibration. Moreover, random blade mistuning due to unavoidable inaccuracies in manufacture or material inhomogeneities can severely increase the maximum forced blade vibration amplitude compared to the tuned counterpart. Unfortunately, this response magnification may worsen in case of small damping. Since modes exhibiting blade dominated vibration are usually considered vulnerable in this regard, the influence of disk and shaft and its mounting conditions seems to be negligible. In this paper, reduced order models are employed in order to simulate the forced response of a radial turbine wheel. Experimental modal analyses have been carried out to provide realistic damping ratios considering both the single turbine wheel hardware as well as the full rotor mounted in a turbocharger test rig. Test runs are conducted and non-intrusive blade-tip-timing technology provides measurement data to validate the simulation models. Contrary to the original presumption, it is shown that additional structural damping contributed by assembling can significantly influence the forced response even though the focus is on blade dominated vibration. Y1 - 2023 U6 - https://doi.org/10.33737/gpps23-tc-138 SN - 2504-4400 ER - TY - GEN A1 - Gambitta, Marco A1 - Beirow, Bernd A1 - Schrape, Sven T1 - Modelling Method for Aeroelastic Low Engine Order Excitation Originating from Upstream Vanes’ Geometrical Variability T2 - International Journal of Turbomachinery Propulsion and Power N2 - The manufacturing geometrical variability in axial compressors is a stochastic source of uncertainty, implying that the real geometry differs from the nominal design. This causes the real geometry to lose the ideal axial symmetry. Considering the aerofoils of a stator vane, the geometrical variability affects the flow traversing it. This impacts the downstream rotor, especially when considering the aeroelastic excitation forces. Optical surface scans coupled with a parametrisation method allow for acquiring the information relative to the real aerofoils geometries. The measured data are included in a multi-passage and multi-stage CFD setup to represent the mistuned flow. In particular, low excitation harmonics on the rotor vane are introduced due to the geometrical deviations of the upstream stator. The introduced low engine orders, as well as their amplitude, depend on the stator geometries and their order. A method is proposed to represent the phenomena in a reduced CFD domain, limiting the size and number of solutions required to probabilistically describe the rotor excitation forces. The resulting rotor excitation forces are reconstructed as a superposition of disturbances due to individual stator aerofoils geometries. This indicates that the problem is linear in the combination of disturbances from single passages. KW - Aeroelasticity KW - Low Engine Order KW - Geometrical Variability Y1 - 2024 U6 - https://doi.org/10.3390/ijtpp9020012 SN - 2504-186X N1 - BTU-interne Projekt-Nr. 35059006 VL - 9 IS - 2 ER - TY - GEN A1 - Gambitta, Marco A1 - Beirow, Bernd A1 - Schrape, Sven T1 - Modelling method for aeroelastic low engine order excitation originating from upstream Vanes’ geometrical variability T2 - International Journal of Turbomachinery Propulsion and Power N2 - The manufacturing geometrical variability in axial compressors is a stochastic source of uncertainty, implying that the real geometry differs from the nominal design. This causes the real geometry to lose the ideal axial symmetry. Considering the aerofoils of a stator vane, the geometrical variability affects the flow traversing it. This impacts the downstream rotor, especially when considering the aeroelastic excitation forces. Optical surface scans coupled with a parametrisation method allow for acquiring the information relative to the real aerofoils geometries. The measured data are included in a multi-passage and multi-stage CFD setup to represent the mistuned flow. In particular, low excitation harmonics on the rotor vane are introduced due to the geometrical deviations of the upstream stator. The introduced low engine orders, as well as their amplitude, depend on the stator geometries and their order. A method is proposed to represent the phenomena in a reduced CFD domain, limiting the size and number of solutions required to probabilistically describe the rotor excitation forces. The resulting rotor excitation forces are reconstructed as a superposition of disturbances due to individual stator aerofoils geometries. This indicates that the problem is linear in the combination of disturbances from single passages. KW - Aeroelasticity KW - Low Engine Order KW - Geometrical Variability Y1 - 2024 SN - 2504-186X VL - 2024 ER - TY - GEN A1 - Sasakaros, Marios A1 - Schafferus, Markus A1 - Wirsum, Manfred A1 - Zobel, Arthur A1 - Vogt, Damian A1 - Nakos, Alex A1 - Beirow, Bernd T1 - Experimental Investigation of Synchronous-Flow-Induced Blade Vibrations on a Radial Turbine T2 - International Journal of Turbomachinery, Propulsion and Power N2 - In this study, a thorough experimental investigation of the synchronous blade vibrations of a radial turbine is performed for different IGV configurations. First, the blade modes are measured experimentally and calculated numerically. Subsequently, the vibrations are recorded with two redundant measurement systems during real operation. Strain gauges were applied on certain blades, while a commercial blade-tip-timing system is used for the measurement of blade deflections. The experimentally determined vibration properties are compared with numerical estimations. Initially, the vibrations recorded with the “nominal” IGV were presented. This IGV primarily generates nodal diameter (ND) 0 vibrations. Subsequently, the impact of two different IGV configurations is examined. First, a mistuned IGV, which has the same number of vanes as the “nominal” IGV is examined. By intentionally varying the distance between the vanes, additional low engine order excitations are generated. Moreover, an IGV with a higher number of vanes is employed to induce excitations at higher frequency modes and ND6 vibrations. Certain vibrations are consistently measured across all IGV configurations, which cannot be attributed to the spiral turbine casing. In addition, a turbine–compressor interaction has been observed. Y1 - 2024 U6 - https://doi.org/10.3390/ijtpp9040035 SN - 2504-186X VL - 9 IS - 4 PB - MDPI AG ER - TY - GEN A1 - Gambitta, Marco A1 - Beirow, Bernd A1 - Klauke, Thomas T1 - Structural dynamics of an axial compressor’s rear blisk drum and multi-stage coupling T2 - ASME Turbo Expo 2024: Turbomachinery Technical Conference and Exposition, June 24–28, 2024, London, United Kingdom Y1 - 2024 SN - 978-0-7918-8803-2 U6 - https://doi.org/10.1115/GT2024-128647 ER - TY - GEN A1 - Beirow, Bernd A1 - Nakos, Alex A1 - Golze, Mark A1 - Vogt, Damian A1 - Wirsum, Manfred A1 - Schafferus, Markus A1 - Sasakaros, Marios T1 - Forced response reduction of a turbine impeller T2 - Advances in Mechanism Design IV, Proceedings of TMM 2024 Y1 - 2024 SN - 978-3-031-70253-2 SN - 978-3-031-70250-1 U6 - https://doi.org/10.1007/978-3-031-70251-8_6 SN - 2211-0984 SP - 53 EP - 65 PB - Springer CY - Cham ER - TY - GEN A1 - Kober, Markus A1 - Beirow, Bernd A1 - Meyer, Marcus A1 - Singh, Kai T1 - Towards the Isogeometric Aero-Engine T2 - Results in Engineering N2 - Creating very detailed finite element models of aero-engines is a very time-consuming process especially if structured meshes have to be generated for thousands of parts. Isogeometric analysis offers the possibility of an accelerated model creation process while achieving higher accuracy by using the non-uniform rational B-spline functions used for the geometry description also as basis functions for the finite element analysis. In this case, no meshing is necessary anymore. Here, we demonstrate this process by applying a self-developed tool which creates a geometry description and a computational model of a part at the same time. By the help of this tool we build up a simplified mechanical aero-engine model, which is used for transient implicit computations simulating the acceleration process of the rotor. We discuss the results as well as the computational time of isogeometric models in comparison to classical finite element models. KW - Isogeometric analysis KW - Finite element method KW - Aero-engine model generation KW - Accelerated whole-engine modeling Y1 - 2023 UR - https://www.sciencedirect.com/science/article/pii/S2590123023002621?via%3Dihub U6 - https://doi.org/10.1016/j.rineng.2023.101135 SN - 2590-1230 VL - Vol. 18 ER - TY - GEN A1 - Sasakaros, Marios A1 - Schafferus, Markus A1 - Wirsum, Manfred A1 - Zobel, Arthur A1 - Vogt, Damian A1 - Nakos, Alex A1 - Beirow, Bernd T1 - Experimental Investigation of Synchronous Flow Induced Blade Vibrations on a Radial Turbine - Part 2: Influence of Different Inlet Guide Vane Configurations T2 - Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023, Volume 11, A. Aerodynamics excitation and damping, bearing and seal dynamics N2 - The occurrence of blade vibrations in radial turbines leads to limit cycle oscillations, which in time increase the risk of component failure due to high cycle fatigue. In this context, the precise determination of the resonance operating points and the estimation of the vibration magnitudes are essential for an accurate assessment of the service life of the turbocharger components. In radial turbines forced blade vibrations are primarily flow induced. These vibrations are produced by the non-uniform flow field in the circumferential direction which acts on the blades as a cyclic pressure fluctuation. Previous studies have identified the inlet guide vane (IGV) and the spiral turbine housing as the primary sources of the non-uniform flow field. In the present study a thorough experimental investigation of the synchronous blade vibrations of a radial turbine is performed. First, the blade vibration modes were measured experimentally and calculated numerically for the determination of the speed ranges that need to be examined. Subsequently, the vibrations were captured with two redundant measurement systems during real turbocharger operation. Strain gauges were applied on certain blades while eight optical sensors were distributed on the circumference of the turbine shroud for the measurement of the blades tips deflection through a commercial tip-timing system. In the first part, the blade vibrations caused by the “nominal” IGV are presented. Part 2 analyses the changes of the blade vibrations due to the application of two different IGVs. The first IGV has the same number of vanes as the “nominal” IGV. Nevertheless, it generates additional low engine order excitations by intentionally varying the distance between the vanes. Next, an IGV with a higher number of vanes is employed for the excitation at higher frequencies and thus of higher blade modes. Contrary to expectations, certain synchronous vibrations can be measured in the experiments of all IGVs. These cannot be attributed to the spiral turbine casing. KW - synchronous blade vibrations KW - flow induced vibrations KW - mistuning Y1 - 2023 SN - 978-0-7918-8705-9 U6 - https://doi.org/10.1115/GT2023-102243 N1 - Projekt Nr. BTU: 35057002 FVV/AiF-Projekt PB - ASME CY - New York ER - TY - GEN A1 - Schafferus, Markus A1 - Sasakaros, Marios A1 - Wirsum, Manfred A1 - Zobel, Arthur A1 - Vogt, Damian A1 - Nakos, Alex A1 - Beirow, Bernd T1 - Experimental Investigation of Synchronous Flow Induced Blade Vibrations on a Radial Turbine - Part 1: Nominal Inlet Guide Vane T2 - Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023, Volume 11, A. Aerodynamics excitation and damping, bearing and seal dynamics N2 - The service life of today’s turbochargers is limited among other things by the mechanical load caused by blade vibrations. In this context, the precise determination of the resonance operating points and the estimation of the vibration magnitudes are essential for an accurate assessment of the service life of the turbocharger components. Forced blade vibrations in radial turbines are primarily flow induced. Flow induced blade vibrations are caused by the nonuniform flow field in the circumferential direction which acts on the blades as a cyclic pressure fluctuation. Previous studies identified the inlet guide vane (IGV) as well as the spiral turbine housing as the primary sources of the non-uniform flow field. In the present study a thorough experimental investigation of the synchronous blade vibrations of a radial turbine is performed. A detailed description of the experimental setup is given. In this setup the vibrations are captured with two redundant measurement systems during real turbocharger operation. Strain gauges, applied on certain blades, as well as optical tip-timing sensors distributed on the circumference of the turbine shroud are used. The advantages of the combined usage of these two measuring systems are shown in the paper. Initially, the blade vibration modes are determined experimentally in stand still tests and numerically calculated through FEM models. This served for the creation of a Campbell diagram, which determined the speed ranges that are examined. The mistuning, which is not taken into account in the numerics, is therefore determined via the experiment. In addition, the experimental results are compared with those of numerics and the frequencies from standstill test. The first part of this two-part paper is focused on the vibrations caused by the “nominal” IGV. This “nominal” IGV has twice the number of blades compared to the rotor. Part 2 will analyze the changes of the blade vibrations due to the application of two different IGVs. Y1 - 2023 SN - 978-0-7918-8705-9 U6 - https://doi.org/10.1115/GT2023-103037 PB - ASME CY - New York ER - TY - GEN A1 - Zobel, Arthur A1 - Fuhrer, Christopher A1 - Vogt, Damian A1 - Nakos, Alex A1 - Beirow, Bernd A1 - Blessing, Alexander A1 - Zippack, Carolin T1 - On the Influence of Bearing Modeling Details on the Dynamical System Effects of a Mid-Size Turbocharger Rotor T2 - Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023, Volume 11, A. Aerodynamics excitation and damping, bearing and seal dynamics N2 - The investigation of the excitation of turbocharger rotors to quantify the High-Cycle-Fatigue (HCF) risk is still a demanding task nowadays. The common way to investigate such phenomena is to look either at the turbine or the compressor rotor in an isolated manner. This approach gives mostly reliable results, if the investigated excitation pattern is stemming from the up- or downstream parts in the machine. However, there is a lack of studies on the existence of responses, which may exist due to the coupling between compressor and turbine. With the increase of computational capabilities and the improvement of FE tools, it is possible to create a full rotor model featuring the compressor and the turbine wheel as well as the bearings to investigate the dynamical behavior of the full rotor at different resonances. To carry out such an investigation, both wheels and the shaft are modeled. The axial, as well as the radial bearings, are modelled realistically by suitable elements and values. Due to the asymmetry of damping and stiffness properties, the resulting system matrices are asymmetrical as well. The eigenfrequencies and mode shapes of such a system can be obtained in a reasonable time by carrying out a modal analysis using the QR damp eigensolver in Ansys APDL. The present paper will show the differences in dynamical system effects of a mid-size turbocharger with different shaft support conditions. For this purpose, the FE simulation with the full rotor and fixed support at the radial bearing position, which is comparable to the isolated rotor consideration, will be compared to the model featuring the detailed bearing modeling with stiffness and damping values originating from the OEM. Besides the detailed process of modeling the bearings, the mutual influence of both rotor wheels at certain eigenfrequencies is analyzed. This allows to conclude on the level of detailing needed to ensure that dynamical system effects are properly accounted. KW - Bearings KW - Dynamic Systems KW - Modeling KW - Rotors Y1 - 2023 SN - 978-0-7918-8705-9 U6 - https://doi.org/10.1115/GT2023-102098 PB - ASME CY - New York ER - TY - GEN A1 - Gambitta, Marco A1 - Beirow, Bernd A1 - Klauke, Thomas T1 - Investigation of Rear Blisk Drum Dynamics Under Consideration of Multi-Stage Coupling T2 - ASME Journal of Engineering for Gas Turbines and Power N2 - The analysis of the structural dynamics of multistage cyclic structures as linked components is required to model the interstage coupling. In turbomachinery, this can result in a collaboration between different compressor or turbine stages. This paper investigates the coupling between two rear drum blade integrated disk stages of an axial compressor to support the mechanical design process. Considering the vibration modeshapes of a multistage system, different components may coparticipate in the dynamics. For this reason, criteria to identify the modes affected by the coupling and to quantify this coupling are defined. This allows to distinguish between modes with interstage coupling, requiring the multistage system for their description, and uncoupled modes, involving a single stage. In addition, it is of interest to research methods to reduce the impact of the coupling on the vibrating system without drastically altering the geometry of the components. The vibration analyses of a two-stage compressor generalized geometry, representative of a compressor rear drum blisk, are presented as a study case. The use of a reducing method allows to describe the behavior of the nominal multistage system with a computationally efficient technique, enabling a parametric analysis of the stages' coupling. The investigation considers the effect of a set of geometrical and mechanical parameters on the dynamics, identifying the driving parameters of the coupled vibration characteristics. Y1 - 2024 U6 - https://doi.org/10.1115/1.4063633 VL - 146 IS - 2 ER - TY - GEN A1 - Gambitta, Marco A1 - Beirow, Bernd A1 - Schrape, Sven T1 - Modelling Method for Aeroelastic Low Engine Order Excitation Originating from Upstream Vanes’ Geometrical Variability T2 - Preprints : the multidisciplinary preprint platform N2 - The manufacturing geometrical variability in axial compressors is a stochastic source of uncertainty, implying that the real geometry differs from the nominal design. This causes the real geometry to lose the ideal axial symmetry. Considering the aerofoils of a stator vane, the geometrical variability affects the flow traversing it. This impacts the downstream rotor, especially when considering the aeroelastic excitation forces. Optical surface scans coupled with a parametrization method allow for acquiring the information relative to the real aerofoils geometries. The measured data are included in a multi-passage and multi-stage CFD setup to represent the mistuned flow. In particular, low excitation harmonics on the rotor vane are introduced due to the geometrical deviations of the upstream stator. The introduced low engine orders as well as their amplitude depend on the stator geometries and their order. A method is proposed to represent the phenomena in a reduced CFD domain, limiting the size and number of solutions required to probabilistically describe the rotor excitation forces. The resulting rotor excitation forces are reconstructed as a superposition of disturbances due to individual stator aerofoils geometries. This indicates that the problem is linear in in the combination of disturbances from single passages. KW - Aeroelasticity KW - Low Engine Order KW - Geometrical Variability Y1 - 2023 U6 - https://doi.org/10.20944/preprints202311.0493.v1 SN - 2310-287X VL - 2023 ER - TY - GEN A1 - Sasakaros, Marios A1 - Becker, Jonte A1 - Wirsum, Manfred A1 - Beirow, Bernd T1 - On the determination of nodal diameter spectrum and mistuning quantification of synchronous blade vbrations through blade-tip-timing measurements T2 - Journal of engineering for gas turbines and power N2 - Synchronous vibrations can severely impact the service life of impellers. Previous studies have demonstrated that mistuning significantly influences the nodal diameter of these vibrations. Mistuned impellers exhibit forced vibration responses comprising multiple nodal diameters, leading to asymmetric vibration expression among the impeller sectors and substantial amplitude overshoots. BTT is a promising technique for monitoring synchronous vibrations due to its non-intrusive nature and capability to monitor all blades simultaneously. This paper presents a novel method for calculating the NDS of synchronous blade vibrations through BTT measurements. The method utilizes the vibration properties, which are estimated via BTT through the Circumferential Fourier Fit method, to reconstruct the blade vibrations. Since the vibration properties of the blades are not determined at the same time, the vibrations are synchronized to acquire the impeller ODS. Subsequently, the NDS is determined by performing DFT analysis on the impeller ODS. Simulated data are used to assess the effect of the vibration sample point on the DFT results and the impact of noise. Based on these results a strategy for the determination of the NDS in a revolution is derived. Next, the method is applied to experimental data acquired from a turbocharger test bench. To investigate the consistency of the proposed method, the results of multiple datasets of the same vibration are presented. In addition, the method is validated by comparing the experimental results with those acquired by forced response simulations. Finally, by employing the experimentally determined impeller ODS and the NDS, mistuning quantification factors are calculated. Y1 - 2025 U6 - https://doi.org/10.1115/1.4069620 SN - 0742-4795 SP - 1 EP - 15 PB - ASME International CY - New York, NY ER - TY - GEN A1 - Beirow, Bernd A1 - Nakos, Alex A1 - Stecklina, Caroline A1 - Noack, Martin A1 - Firl, Matthias A1 - Sasakaros, Marios T1 - Implementation of intentional mistuning by means of finite element based shape optimization T2 - Journal of engineering for gas turbines and power N2 - Intentional Mistuning has turned out to be an effective measure to alleviate the maximum forced response of bladed wheels in the framework of numerous studies in the past. In particular solutions based on two different blade designs, following e.g. alternating or AABB patterns, have proved to be promising in this regard and moreover robust against the impact of unavoidable random mistuning. Thus, for example, a 40 percent reduction of the first blade bending maximum forced response has been proved experimentally for a turbine impeller of a turbo charger application. Despite this success, the technical implementation of the frequency based mistuning pattern followed an academic solution based on locally removing material at the leading edge tip, which is not suited for the use in serial wheels since it may disturb the flow channel. In addition, the forced response of other blade modes may be affected in a negative manner. In order to overcome these problems, an alternative way of implementing Intentional Mistuning is suggested by applying a marginal geometric modification of the blade thickness distribution to adjust the natural frequency of the first bending mode. Finite element based shape optimization is utilized to this end. Secondary conditions are ensuring that only the target frequency of the first bending mode is adjusted whereas natural frequencies of other modes are kept almost unchanged. Y1 - 2025 U6 - https://doi.org/10.1115/1.4069624 SN - 0742-4795 SP - 1 EP - 15 PB - ASME International CY - New York ER - TY - GEN A1 - Nakos, Alex A1 - Beirow, Bernd T1 - Comparative experimental determination of mistuning of a bladed turbine wheel using different evaluation approaches T2 - Journal of engineering for gas turbines and power N2 - Random mistuning of integrally manufactured turbine and compressor wheels can lead to severely high magnitudes in blade vibration. In order to be able to calculate the vibration response of bladed wheels correctly the actual mistuning should be quantified most accurately and taken into account e.g. in simulation models. An industry-suited procedure has been introduced by Kühhorn and Beirow [1] which modifies a conventional experimental modal analysis by isolating the blade that is excited and measured from all remaining ones. This enables the often coupled frequency response function peaks to decouple and obtain only one single peak which marks the actual frequency mistuning of the blade. Indeed, the procedure has proved to be accurate if isolated blade mode families are considered. In other cases, blade-disk-coupling can still be a problem and falsify the evaluation. The reason for this is an unfavourable application of the additional masses which most often cannot be avoided and may lead to an inaccurate or even erroneous mistuning value. However, Zhou et al. [2] have developed a novel approach to calculate an error term in order to correct the measured frequency mistuning. In this paper a radial turbine wheel is subjected to the blade frequency tests. The evaluation is carried out by using both, the conventional evaluation of the frequency response function and the novel approach. Finally, the impact and measurement falsification of additional masses when testing a radial turbine wheel is discussed. Y1 - 2025 U6 - https://doi.org/10.1115/1.4069626 SN - 0742-4795 SP - 1 EP - 13 PB - ASME International CY - New York, NY ER - TY - GEN A1 - Sasakaros, Marios A1 - Becker, Jonte A1 - Wirsum, Manfred A1 - Beirow, Bernd T1 - On the determination of nodal diameter spectrum and mistuning quantification of synchronous blade vbrations through blade-tip-timing measurements BT - Volume 9 : structures and dynamics : structural mechanics & vibration; supercritical CO2 T2 - Proceedings of the ASME Turbo Expo 2025, Memphis, June 16–20, 2025 N2 - Synchronous vibrations can severely impact the service life of impellers. Previous studies have demonstrated that mistuning significantly influences the nodal diameter of these vibrations. Specifically, mistuned impellers exhibit forced vibration responses comprising multiple nodal diameters, leading to asymmetric vibration expression among the impeller sectors and substantial amplitude overshoots. Blade-Tip-Timing (BTT) is a promising technique for monitoring synchronous vibrations due to its non-intrusive nature and capability to monitor all blades simultaneously. This paper presents a novel method for calculating the Nodal Diameter Spectrum (NDS) of synchronous blade vibrations through BTT measurements. The method utilizes the vibration properties, which are estimated via BTT through the Circumferential Fourier Fit method, to reconstruct the blade vibrations. Since the vibration properties of the blades are not determined at the same time, the vibrations are synchronized to acquire the impeller Operational Deflection Shape (ODS), which can be associated with the mistuned impeller modes at the resonance crossings. Subsequently, the NDS is determined by performing Discrete Fourier Transform (DFT) analysis on the impeller ODS. Simulated data are used to assess the effect of the vibration sample point on the DFT results and the impact of noise. Based on these results a strategy for the determination of the NDS in a revolution is derived. Next, the method is applied to experimental data acquired from a turbocharger test bench. To investigate the consistency of the proposed method, the results of multiple datasets of the same vibration are presented. In addition, the method is validated by comparing the experimental results with those acquired by forced response simulations. Finally, by employing the experimentally determined impeller ODS and the NDS, mistuning quantification factors are calculated. KW - Blade-Tip-Timing KW - Synchronous Blade Vibrations KW - Nodal Diameter KW - Nodal Diameter Spectrum KW - Mistuning Y1 - 2025 SN - 978-0-7918-8885-8 U6 - https://doi.org/10.1115/GT2025-151774 PB - The American Society of Mechanical Engineers CY - New York, NY ER - TY - GEN A1 - Nakos, Alex A1 - Beirow, Bernd T1 - Comparative experimental determination of mistuning of a bladed turbine wheel using different evaluation approaches BT - Volume 9 : structures and dynamics : structural mechanics & vibration; supercritical CO2 T2 - Proceedings of the ASME Turbo Expo 2025, Memphis, June 16–20, 2025 N2 - Random mistuning of integrally manufactured turbine and compressor wheels can lead to severely high magnitudes in blade vibration. This is caused by unavoidable imperfections due to manufacturing processes or material inhomogeneities and the resulting deviation in geometry and structure between the individual blades. In order to be able to calculate the vibration response of bladed wheels correctly the actual mistuning should be quantified most accurately and taken into account e.g. in simulation models. Since mistuning is usually described as a frequency deviation of the nominal value measuring procedures have been developed in order to measure existing wheel hardware. An industry-suited procedure has been introduced by Kühhorn and Beirow [1] which modifies a conventional experimental modal analysis by isolating the blade that is excited and measured from all remaining ones. Therefore, additional masses are applied in order to cause a detuning and thus an isolated vibration of the blade under consideration. This enables the often coupled frequency response function peaks to decouple and obtain only one single peak which marks the actual frequency mistuning of the blade. Indeed, the procedure has proved to be accurate if isolated blade mode families are considered. In other cases, blade-disk-coupling can still be a problem and falsify the evaluation. The reason for this is an unfavourable application of the additional masses which most often cannot be avoided and may lead to an inaccurate or even erroneous mistuning value. However, Zhou et al. [2] have developed a novel approach to calculate an error term in order to correct the measured frequency mistuning. In this paper a radial turbine wheel is subjected to the blade frequency tests. The evaluation is carried out by using both, the conventional evaluation of the frequency response function and the novel approach. The error term is calculated and the mistuning distributions were corrected. Finally, the impact and measurement falsification of additional masses when testing a radial turbine wheel is discussed. KW - Mistuning KW - Blade Vibration KW - Damping KW - Modal Analyses Y1 - 2025 SN - 978-0-7918-8885-8 U6 - https://doi.org/10.1115/GT2025-151778 PB - The American Society of Mechanical Engineers CY - New York, NY ER - TY - GEN A1 - Beirow, Bernd A1 - Nakos, Alex A1 - Stecklina, Caroline A1 - Noack, Martin A1 - Firl, Matthias A1 - Sasakaros, Marios T1 - Implementation of intentional mistuning by means of finite element based shape optimization BT - Volume 9 : structures and dynamics : structural mechanics & vibration; supercritical CO2 T2 - Proceedings of the ASME Turbo Expo 2025, Memphis, June 16–20, 2025 N2 - Intentional Mistuning has turned out to be an effective measure to alleviate the maximum forced response of bladed wheels in the framework of numerous studies in the past. In particular solutions based on two different blade designs, following e.g. alternating or AABB patterns, have proved to be promising in this regard and moreover robust against the impact of unavoidable random mistuning. Thus, for example, a 40 percent reduction of the first blade bending maximum forced response has been proved experimentally for a turbine impeller of a turbo charger application. Despite this success, the technical implementation of the frequency based mistuning pattern followed an academic solution based on locally removing material at the leading edge tip, which is not suited for the use in serial wheels since it may disturb the flow channel. In addition, the forced response of other blade modes may be affected in a negative manner. In order to overcome these problems, an alternative way of implementing Intentional Mistuning is suggested by applying a marginal geometric modification of the blade thickness distribution to adjust the natural frequency of the first bending mode. Finite element based shape optimization is utilized to this end. Secondary conditions are ensuring that only the target frequency of the first bending mode is adjusted whereas natural frequencies of other modes are kept almost unchanged. KW - Intentional Mistuning KW - Turbine Impeller KW - Forced Response KW - Shape Optimization Y1 - 2025 SN - 978-0-7918-8885-8 U6 - https://doi.org/10.1115/GT2025-151617 PB - The American Society of Mechanical Engineers CY - New York, NY ER -