@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{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{NakosBeirowWirsumetal., author = {Nakos, Alex and Beirow, Bernd and Wirsum, Manfred and Schafferus, Markus and Sasakaros, Marios and Vogt, Damian and Zobel, Arthur}, title = {Mistuning and Damping of a Radial Turbine Wheel. Part 3: Validation of Intentional Mistuning During Machine Operation}, series = {Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023}, journal = {Proceedings of ASME Turbo Expo 2023, Boston, Massachusetts, June 26-30, 2023}, isbn = {978-0-7918-8706-6}, doi = {10.1115/GT2023-101993}, abstract = {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.}, 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} }