@misc{KoberBeirowMeyeretal., author = {Kober, Markus and Beirow, Bernd and Meyer, Marcus and Singh, Kai}, title = {Towards the Isogeometric Aero-Engine}, series = {Results in Engineering}, volume = {Vol. 18}, journal = {Results in Engineering}, issn = {2590-1230}, doi = {10.1016/j.rineng.2023.101135}, abstract = {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.}, language = {en} } @misc{SasakarosSchafferusWirsumetal., author = {Sasakaros, Marios and Schafferus, Markus and Wirsum, Manfred and Zobel, Arthur and Vogt, Damian and Nakos, Alex and Beirow, Bernd}, title = {Experimental Investigation of Synchronous Flow Induced Blade Vibrations on a Radial Turbine - Part 2: Influence of Different Inlet Guide Vane Configurations}, series = {Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023, Volume 11, A. Aerodynamics excitation and damping, bearing and seal dynamics}, journal = {Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023, Volume 11, A. Aerodynamics excitation and damping, bearing and seal dynamics}, publisher = {ASME}, address = {New York}, isbn = {978-0-7918-8705-9}, doi = {10.1115/GT2023-102243}, pages = {15}, abstract = {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.}, language = {en} } @misc{SchafferusSasakarosWirsumetal., author = {Schafferus, Markus and Sasakaros, Marios and Wirsum, Manfred and Zobel, Arthur and Vogt, Damian and Nakos, Alex and Beirow, Bernd}, title = {Experimental Investigation of Synchronous Flow Induced Blade Vibrations on a Radial Turbine - Part 1: Nominal Inlet Guide Vane}, series = {Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023, Volume 11, A. Aerodynamics excitation and damping, bearing and seal dynamics}, journal = {Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023, Volume 11, A. Aerodynamics excitation and damping, bearing and seal dynamics}, publisher = {ASME}, address = {New York}, isbn = {978-0-7918-8705-9}, doi = {10.1115/GT2023-103037}, pages = {13}, abstract = {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.}, language = {en} } @misc{ZobelFuhrerVogtetal., author = {Zobel, Arthur and Fuhrer, Christopher and Vogt, Damian and Nakos, Alex and Beirow, Bernd and Blessing, Alexander and Zippack, Carolin}, title = {On the Influence of Bearing Modeling Details on the Dynamical System Effects of a Mid-Size Turbocharger Rotor}, series = {Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023, Volume 11, A. Aerodynamics excitation and damping, bearing and seal dynamics}, journal = {Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023, Volume 11, A. Aerodynamics excitation and damping, bearing and seal dynamics}, publisher = {ASME}, address = {New York}, isbn = {978-0-7918-8705-9}, doi = {10.1115/GT2023-102098}, pages = {11}, abstract = {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.}, language = {en} } @misc{GambittaBeirowKlauke, author = {Gambitta, Marco and Beirow, Bernd and Klauke, Thomas}, title = {Investigation of Rear Blisk Drum Dynamics Under Consideration of Multi-Stage Coupling}, series = {ASME Journal of Engineering for Gas Turbines and Power}, volume = {146}, journal = {ASME Journal of Engineering for Gas Turbines and Power}, number = {2}, doi = {10.1115/1.4063633}, pages = {8}, abstract = {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.}, language = {en} } @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} }