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 - RPRT A1 - Nakos, Alex A1 - Schafferus, Markus A1 - Sasakaros, Marios A1 - Zobel, Arthur T1 - Intentional Mistuning zur Begrenzung erzwungener Schwingungsantworten von Radialturbinen T2 - Abschluss- und Zwischenberichte der Forschungsstellen : Frühjahrstagung 2022 : Tagungsband, FVV 2022 Spring Conference, March 30-31, 2022, Würzburg, Germany Final and interim reports presented by the RTD performers engines N2 - Im Vordergrund des Forschungsprojekts steht die Reduktion der Schwingungsantwort einer Radialtur-bine. Die in den Vorgängervorhaben [1], [2] und [3] gewonnen Erkenntnisse und Methoden hinsichtlich des auftretenden Mistunings sollen auf die betrachtete Radialturbine übertragen und angewendet wer-den, sodass die zu erwartenden Schwingungsüberhöhungen dargestellt werden können. Aufbauend auf die drei Vorgängervorhaben soll zusätzlich erstmalig die erfolgreiche Umsetzung von Intentional Mistuning (IM) untersucht werden, welches das Potential besitzt die Schwingungsantwort drastisch re-duzieren zu können. Auf Basis von numerischen Modalanalysen unter Verwendung der finiten Element-Methode werden Be-rechnungsmodelle erstellt, mit denen das Schwingungsverhalten beschrieben und ebenfalls ein geeig-netes Bearbeitungsmuster zur Umsetzung von IM erzielt werden kann. Diese stellen die Basis zur Er-arbeitung einer geometrischen Anpassung eines Versuchsträgers dar. Da die Strukturdämpfung bei Radiallaufrädern im Hinblick auf Schaufelschwingungen verschwindend gering ausfällt, ist die aerodynamische Dämpfung von großer Bedeutung und liefert einen entscheiden-den Beitrag zur entsprechenden Schwingungsüberhöhung bzw. -reduktion. Mit Hilfe numerischer Strö-mungssimulationen werden aerodynamische Dämpfungskurven unter Betriebsbedingungen berechnet, welche im Rahmen der numerischen Simulationen zur Entwicklung geeigneter IM-Modifikationen mit-berücksichtigt werden. Bei den Versuchsträgern handelt es sich um zwei baugleiche Radialturbinen eines Abgasturboladers gleicher Serie, welche im Rahmen von Schwingungsuntersuchungen im Stillstand sowie unter Betriebs-bedingungen untersucht werden sollen. Dabei dient ein Laufrad als unbearbeitete „getunte“ Referenz, an der die Schwingungsantwort des zweiten bearbeiteten Laufrades validiert werden soll. Im Rahmen von Schwingungsuntersuchungen bei Stillstand unter Laborbedingungen werden erste Analysen hin-sichtlich der erfolgreichen Umsetzung des IM vorgenommen, welche im späteren Verlauf des Projektes durch Messungen auf einem Prüfstand ergänzt werden. Dabei soll die Wirksamkeit der Anwendung von IM unter Betriebsbedingungen untersucht und nachgewiesen werden. Hierfür wird ein am IKDG der RWTH Aachen betriebener Abgasturboladerprüfstand an die spezifischen Anforderungen des aktuellen Turboladers angepasst und mit erforderlicher Messtechnik ausgerüstet. Da die aerodynamische Dämpfung maßgeblich ist für das Schwingungsverhalten von Radiallaufrädern in Integralbauweise, werden experimentelle Modalanalysen unter veränderlichem Umgebungsdruck durchgeführt und auf der Basis hieraus abgeleiteter modaler Parameter eine Formel weiterentwickelt, welche eine Abschätzung des Dämpfungsniveaus während der Entwicklungsphase ermöglichen soll. Ziel hierbei ist die Möglichkeit zur Bewertung des zu erwartenden Schwingungsniveaus in frühen Sta-dien der Laufradentwicklung. Y1 - 2022 N1 - Zwischenbericht, FVV Nr. 1389, Projekt-Nr. (BTU) 35057002 PB - Forschungsvereinigung Verbrennungskraftmaschinen e.V. (FFV) CY - Frankfurt am Main 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 - 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 -