The effects of temporal fluid inertia on tilting pad journal bearing dynamics

Abstract

Rotordynamic predictions on machines supported by fluid film bearings typically rely on models that solve the Reynolds equation to determine the bearing dynamics. The Reynolds equation is derived from the thin film momentum equation that assumes fluid inertia terms can be totally neglected because the reduced Reynolds number is very small. This paper examines the impact of including temporal fluid inertia on tilting pad bearings that are widely used in the applications of concern. Using the small perturbation method, a new form of the perturbed equation is developed for easy application to tilting pad journal bearings. The temporal fluid inertia leads to a set of full added mass coefficients and modifications to the damping coefficients. When applied to a typical 5-pad, tilting pad bearing, it is found that the influence of temporal inertia increases with the increase of shaft whirl frequency. Its impact is also dependent on the magnitude of the added mass coefficients relative to the magnitudes of its stiffness and damping. Therefore, temporal fluid inertia effects could be important for high speed, light rotor applications, as well as applications using low viscosity fluids, such as water.