Excitation mechanisms of non-linear rotor systems with floating ring bearings - simulation and validation

Abstract

Concerning dynamical systems an integral part of the construction is the support. Due to favourable thermal and mechanical properties, journal bearings are widely used, from steam or gas turbines of power plants over main bearings of combustion engines to automotive exhaust gas turbochargers, with its comparatively small turbines. The latter shows due to the floating ring bearings an increased level of complexity.The focus of the present study lies on the non-linear effects of floating ring bearings, which have a significant influence on the maximum vibration amplitude, especially in the context of fast rotating and/or slightly loaded rotor systems. The typical resonance conditions of linear systems are inadequate for predicting the system’s behaviour and must therefore be supplemented with non-linear effects. The acting principles of subharmonic excitation and their interaction with the eigenfrequencies of rotor systems supported by journal bearings will be investigated and characterised using the example of an exhaust gas turbocharger. Because the mutual influence between rotor system and support is essential for a detailed illustration of the main effects, a holistic simulation for transient conditions is performed including analysis of eigenbehaviour in form of linear and non-linear Campbell diagrams.