Leichtfuss, Sebastian ; Durbiano, Loic ; Kreschel, Martin ; Dielenschneider, Tobias ; Nordmann, Rainer ; Atzrodt, Heiko ; Pilotto, Rafael ; Schiffer, Heinz-Peter (2019)
Advanced measurements and model update of an automotive turbocharger with full-floating journal bearings.
SIRM 2019 – 13th International Conference on Dynamics of Rotating Machines. Copenhagen, Denmark (13.02.2019-15.02.2019)
Konferenzveröffentlichung, Bibliographie

Kurzbeschreibung (Abstract)

Full-floating journal bearings are commonly used in automotive turbochargers. Subsynchronous vibrations in such applications are often caused by oil-whirl and -whip phenomena. The small rotor weight in combination with very high rotational speeds provoke this unstable rotor-bearing behavior. This often leads to high vibration amplitudes, undesired noise or even risks rotor integrity. Models are commonly used to predict the complex nonlinear interaction of shaft, casing, floating-ring and oil film. Those models are based on basics of mechanics, experiences and are normally calibrated with simplified experiments. In this paper a unique set of experimental data are compared to different simulation methods providing an overview of the physical behavior of a typical automotive turbocharger rotor and the model complexity needed to account for such phenomena. Experimental data are gathered at the hot gas test stand at Technische Universitaet Darmstadt. Intensive high-speed instrumentation is used providing information of the relative radial movement of the shaft at both ends of the rotor. Additionally, the rotational speed of both floating rings is monitored, and the axial movement of the shaft is recorded. The turbocharger is operated with realistic oil and gas temperatures and pressures. Acceleration and deceleration sweeps with different aerodynamic throttlings are recorded accounting for varying axial thrust. Experimental results are compared with a model results presented by Koehl 2015 [1] and related to simulation results conducted by the Fraunhofer institute LBF with the simulation tool MADYN 2000. The rotor model by Koehl is using Ritz-Ansatz functions. These ansatz functions have to discretize the rotor eigenmodes and fulfill the geometrical boundary conditions of the rotor system. In MADYN 2000 the rotor is modelled by using the Timoshenko beam theory and Finite-Elements with Hermite polynomials to model properties of the rotor including gyroscopic effects. The forces in the floating bearing system are calculated by integration of the fluid film pressure. Those are derived from the solution of the Reynolds equations numerically solved using the Finite-Volume method.

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