@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} } @techreport{NakosSchafferusSasakarosetal., author = {Nakos, Alex and Schafferus, Markus and Sasakaros, Marios and Zobel, Arthur}, title = {Intentional Mistuning zur Begrenzung erzwungener Schwingungsantworten von Radialturbinen}, series = {Abschluss- und Zwischenberichte der Forschungsstellen : Fr{\"u}hjahrstagung 2022 : Tagungsband, FVV 2022 Spring Conference, March 30-31, 2022, W{\"u}rzburg, Germany Final and interim reports presented by the RTD performers engines}, journal = {Abschluss- und Zwischenberichte der Forschungsstellen : Fr{\"u}hjahrstagung 2022 : Tagungsband, FVV 2022 Spring Conference, March 30-31, 2022, W{\"u}rzburg, Germany Final and interim reports presented by the RTD performers engines}, publisher = {Forschungsvereinigung Verbrennungskraftmaschinen e.V. (FFV)}, address = {Frankfurt am Main}, abstract = {Im Vordergrund des Forschungsprojekts steht die Reduktion der Schwingungsantwort einer Radialtur-bine. Die in den Vorg{\"a}ngervorhaben [1], [2] und [3] gewonnen Erkenntnisse und Methoden hinsichtlich des auftretenden Mistunings sollen auf die betrachtete Radialturbine {\"u}bertragen und angewendet wer-den, sodass die zu erwartenden Schwingungs{\"u}berh{\"o}hungen dargestellt werden k{\"o}nnen. Aufbauend auf die drei Vorg{\"a}ngervorhaben soll zus{\"a}tzlich erstmalig die erfolgreiche Umsetzung von Intentional Mistuning (IM) untersucht werden, welches das Potential besitzt die Schwingungsantwort drastisch re-duzieren zu k{\"o}nnen. 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 Versuchstr{\"a}gers dar. Da die Strukturd{\"a}mpfung bei Radiallaufr{\"a}dern im Hinblick auf Schaufelschwingungen verschwindend gering ausf{\"a}llt, ist die aerodynamische D{\"a}mpfung von großer Bedeutung und liefert einen entscheiden-den Beitrag zur entsprechenden Schwingungs{\"u}berh{\"o}hung bzw. -reduktion. Mit Hilfe numerischer Str{\"o}-mungssimulationen werden aerodynamische D{\"a}mpfungskurven unter Betriebsbedingungen berechnet, welche im Rahmen der numerischen Simulationen zur Entwicklung geeigneter IM-Modifikationen mit-ber{\"u}cksichtigt werden. Bei den Versuchstr{\"a}gern 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 sp{\"a}teren Verlauf des Projektes durch Messungen auf einem Pr{\"u}fstand erg{\"a}nzt werden. Dabei soll die Wirksamkeit der Anwendung von IM unter Betriebsbedingungen untersucht und nachgewiesen werden. Hierf{\"u}r wird ein am IKDG der RWTH Aachen betriebener Abgasturboladerpr{\"u}fstand an die spezifischen Anforderungen des aktuellen Turboladers angepasst und mit erforderlicher Messtechnik ausger{\"u}stet. Da die aerodynamische D{\"a}mpfung maßgeblich ist f{\"u}r das Schwingungsverhalten von Radiallaufr{\"a}dern in Integralbauweise, werden experimentelle Modalanalysen unter ver{\"a}nderlichem Umgebungsdruck durchgef{\"u}hrt und auf der Basis hieraus abgeleiteter modaler Parameter eine Formel weiterentwickelt, welche eine Absch{\"a}tzung des D{\"a}mpfungsniveaus w{\"a}hrend der Entwicklungsphase erm{\"o}glichen soll. Ziel hierbei ist die M{\"o}glichkeit zur Bewertung des zu erwartenden Schwingungsniveaus in fr{\"u}hen Sta-dien der Laufradentwicklung.}, 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} }