Thermohydrodynamic Analysis of Misaligned Journal Bearings

Abstract

Hydrodynamic journal bearings are used to support rotating shafts of machines such as compressors, turbogenerators, pumps, etc. under imposed operating conditions which comprises speed and load. These bearings are normally designed using data developed with the assumptions that they operate with isoviscous lubricants and are aligned. Oil viscosity is a strong function of oil temperature and varies throughout the film. This, in turn, influences the prediction of various bearing performance characteristics. The temperature of the lubricant is largely controlled by the speed of the journal. Since there is a tendency to design rotors to operate at high speeds for optimum performance, the assumption of constant temperature (and hence constant viscosity) appears to be doubtful. Further, due to manufacturing tolerances, deflection of journal and bearing support, asymmetric bearing load, etc., journal bearings may quite often operate at the misaligned condition. The geometry of clearance space between the journal and the bush influences the bearing performance significantly. The clearance geometry depends largely on the amount of misalignment present between the axes of bearing and journal. Therefore, for a more accurate prediction of bearing performance, it is essential to perform a complete thermo hydrodynamic (THD) analysis of misaligned journal be~ings. The present study has been planned with these forethoughts. Although the theory of thermohydrodynamic (THD) lubrication developed quite significantly during the last few decades, it remained confined mainly to the problems of aligned journal bearings. The published literature on the THD investigations on misaligned journal bearings is scant. Even the isothermal literature on misaligned journal bearings is generally limited to the computation of static and dynamic performance characteristics of circular bearing geometries (ie plain and two-axial-groove) only.