Analysis of Hydrodynamic Journal Bearing Including Thermal Effect

Abstract

In hydrodynamic journal bearing, due to shearing action, temperature of the oil film increases. On account of rise in temperature, viscosity of the lubricant is reduced which in turn leads to decrease in load carrying capacity of the film. Hence, for better estimation of bearing performance, thermohydrodynamic (THD) analysis of journal bearing is essential. An appropriate boundary condition should be identified to predict results corresponding to the actual conditions. In this paper, steady-state analysis is presented to study the influence of thermal boundary conditions namely, Adiabatic, Isoadiabatic (ISOADI) and Full thermal (THD), on the simulation results of journal bearing. Finite difference method is used to discretize the governing equations. Generalized Reynolds equation, viscosity-temperature relationship and two dimensional energy equation are solved simultaneously. Correction factor for thermal characteristics in cavitation zone and the energy balance at oil inlet have been taken into consideration. In cases of ISOADI and THD, shaft metal body is assumed as an isothermal surface having a zero net heat flux. Full THD boundary condition is capable to account heat transfer through bush. Effect of eccentricity ratio on performance characteristics have been studied for various thermal boundary cases. Results obtained by including thermal effect have been compared with the isothermal results. Load carrying capacity of the bearing obtained by including thermal effect seems to be realistic and is lower than isothermal solution. It is noticed that performance characteristics of the bearing for Adiabatic, ISOADI and THD cases, have no significant variation. However, maximum temperature within the oil film for adiabatic case is more than ISOADI and THD condition. Comparison between the present results and available experimental results indicate that ISOADI / THD is appropriate and realistic than the adiabatic case.