Vibro-acoustical Behavior of a Turbocharger Housing Excited by Oil-film Induced Rotor Oscillations

This paper deals with the interaction of the turbocharger housing and the rotor to reveal the acoustic phenomena which are excited by the oil whirl/whip instabilities. Therefore, a flexible multibody model is built up for the rotor subsystem which is supported in floating ring bearings. The flexibility of the housing subsystem is taken into account by considering it as a modally reduced structure within the multibody simulation model. Primarily, the two subsystems are simulated sequentially. The first step gives the oil film forces during a typical run-up simulation of the rotor subsystem if the bearing shell deformation is neglected. In a second step, the obtained oil film forces are applied at the decoupled housing structure to analyze the vibro-acoustics of the turbocharger in detail. The vibro-acoustical behavior is judged by the occurring housing amplitudes which are predominantly influenced by the mounting concept of the turbocharger on the engine. It is found out that the subsynchronous excitation due to the oil films can be magnified through the housing structure in a quite wide speed range which is the main excitation mechanism affecting the acoustics of turbochargers. Finally, the run-up simulation is performed for the coupled subsystems of rotor and housing where the oil film forces are also dependent on the local deformation of the bearing housing

On the Importance of Frictional Energy Dissipation in the Prevention of Undesirable Self-Excited Vibrations in Gas Foil Bearing Rotor Systems

In this contribution, a nonlinear and fully coupled fluid–structure–rotor interaction model of a gas foil bearing rotor system is presented. Aiming at the reduction of undesirable self-excited vibrations, many common bearing designs feature a compliant and slightly movable multi-part foil structure inside the lubrication gap. The present paper discusses the general impact of frictional energy dissipation within the foil structure by adding equivalent viscous damping to the widespread simple elastic foundation model. For the computational analysis, the PDEs describing the fluid pressure distribution and the foil structure deformation field are spatially discretized using finite difference schemes. After suitable nondimensionalization of the resulting system of nonlinear ODEs, a corresponding state-space representation is deduced. Using numerical simulation tools, the stability of equilibrium points and the occurrence of self-excited vibrations are addressed and possible bifurcation scenarios are discussed. Summing up all results, frictional energy dissipation proves to be of crucial importance with regard to the reduction or prevention of undesirable self-excited vibrations in gas foil bearing rotor systems