Influence of thermally induced changes in lubricating gap clearance and oil viscosity on nonlinear oscillations of hydrodynamically supported rotors

Abstract

Despite many advantages, hydrodynamic bearings tend to induce nonlinear vibrations on rotor systems at low external loads. The occurrence and also the amplitudes of these vibrations are very sensible to the operating conditions of the system such as occurrence of gaseous cavitation, oil viscosity (strongly dependent on oil temperature), bearing clearance (dependent on metal temperature and thermal expansion coefficients) or rotor imbalance. This contribution shows the calculation of nonlinear rotor oscillations with the help of a detailed transient 3D-thermo-hydrodynamic bearing model. Referring to experimental data of a real exhaust turbocharger with semi-floating ring bearings, this holistic approach is used for a separate investigation of a) the influences of the temperature-dependent oil viscosity in the lubricating films and b) the influences of temperature-related changes in the lubricating gap on the nonlinear oscillations of the rotor.