@misc{GambittaBeirowSchrape, author = {Gambitta, Marco and Beirow, Bernd and Schrape, Sven}, title = {Modelling Method for Aeroelastic Low Engine Order Excitation Originating from Upstream Vanes' Geometrical Variability}, series = {Preprints : the multidisciplinary preprint platform}, volume = {2023}, journal = {Preprints : the multidisciplinary preprint platform}, issn = {2310-287X}, doi = {10.20944/preprints202311.0493.v1}, abstract = {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.}, language = {en} } @misc{SasakarosBeckerWirsumetal., author = {Sasakaros, Marios and Becker, Jonte and Wirsum, Manfred and Beirow, Bernd}, title = {On the determination of nodal diameter spectrum and mistuning quantification of synchronous blade vbrations through blade-tip-timing measurements}, series = {Journal of engineering for gas turbines and power}, journal = {Journal of engineering for gas turbines and power}, publisher = {ASME International}, address = {New York, NY}, issn = {0742-4795}, doi = {10.1115/1.4069620}, pages = {1 -- 15}, abstract = {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.}, language = {en} } @misc{BeirowNakosStecklinaetal., author = {Beirow, Bernd and Nakos, Alex and Stecklina, Caroline and Noack, Martin and Firl, Matthias and Sasakaros, Marios}, title = {Implementation of intentional mistuning by means of finite element based shape optimization}, series = {Journal of engineering for gas turbines and power}, journal = {Journal of engineering for gas turbines and power}, publisher = {ASME International}, address = {New York}, issn = {0742-4795}, doi = {10.1115/1.4069624}, pages = {1 -- 15}, abstract = {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.}, language = {en} } @misc{NakosBeirow, author = {Nakos, Alex and Beirow, Bernd}, title = {Comparative experimental determination of mistuning of a bladed turbine wheel using different evaluation approaches}, series = {Journal of engineering for gas turbines and power}, journal = {Journal of engineering for gas turbines and power}, publisher = {ASME International}, address = {New York, NY}, issn = {0742-4795}, doi = {10.1115/1.4069626}, pages = {1 -- 13}, abstract = {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 K{\"u}hhorn 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.}, language = {en} } @misc{SasakarosBeckerWirsumetal., author = {Sasakaros, Marios and Becker, Jonte and Wirsum, Manfred and Beirow, Bernd}, title = {On the determination of nodal diameter spectrum and mistuning quantification of synchronous blade vbrations through blade-tip-timing measurements}, series = {Proceedings of the ASME Turbo Expo 2025, Memphis, June 16-20, 2025}, journal = {Proceedings of the ASME Turbo Expo 2025, Memphis, June 16-20, 2025}, publisher = {The American Society of Mechanical Engineers}, address = {New York, NY}, isbn = {978-0-7918-8885-8}, doi = {10.1115/GT2025-151774}, pages = {15}, abstract = {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.}, language = {en} } @misc{NakosBeirow, author = {Nakos, Alex and Beirow, Bernd}, title = {Comparative experimental determination of mistuning of a bladed turbine wheel using different evaluation approaches}, series = {Proceedings of the ASME Turbo Expo 2025, Memphis, June 16-20, 2025}, journal = {Proceedings of the ASME Turbo Expo 2025, Memphis, June 16-20, 2025}, publisher = {The American Society of Mechanical Engineers}, address = {New York, NY}, isbn = {978-0-7918-8885-8}, doi = {10.1115/GT2025-151778}, pages = {11}, abstract = {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 K{\"u}hhorn 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.}, language = {en} } @misc{BeirowNakosStecklinaetal., author = {Beirow, Bernd and Nakos, Alex and Stecklina, Caroline and Noack, Martin and Firl, Matthias and Sasakaros, Marios}, title = {Implementation of intentional mistuning by means of finite element based shape optimization}, series = {Proceedings of the ASME Turbo Expo 2025, Memphis, June 16-20, 2025}, journal = {Proceedings of the ASME Turbo Expo 2025, Memphis, June 16-20, 2025}, publisher = {The American Society of Mechanical Engineers}, address = {New York, NY}, isbn = {978-0-7918-8885-8}, doi = {10.1115/GT2025-151617}, pages = {11}, abstract = {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.}, language = {en} }