Effects of the Shaft Speed on Stiffness and Damping Coefficients of Hydrodynamic Bearing-Shaft System under Variable Viscosity

The rotating shaft-hydrodynamic bearings systems operated with high speed and/or heavy load conditions expose serious rotordynamics instability problems due to characteristics of the supporting bearings. The stability and the dynamics of these systems, directly relate to the lubricant properties that are directly affect by the heat generation. The main purpose of this study is investigation of the dynamic characteristics and the stability of a shaft supported by hydrodynamic journal bearing under variable viscosity. Th e equations of lubricant flow were derived by Dowson's model under variable viscosity, and the dynamic characteristics were modelled with the perturbation model in direct and cross directions. The heat transfers between oil and the journal surface was modelled in a 3-dimensional energy and the heat conduction equation. An algorithm based on finite difference and successive-over-relaxation method was developed to solve the theoretical models, simultaneously, and a serial simulation was performed to investigate the variations of the dynamic coefficients of the bearing-shaft system concerning the shaft speed for different radial clearance values. It was determined that the high speed increases the lubricant temperature, and so the static and dynamic performance characteristics decrease, moreover, this effect is more dominant for the smaller radial clearance.