Influence of Cross-Film Viscosity Variation on Conduction Effects in Journal Bearings

Abstract

This paper evaluates the effect of cross-film viscosity and temperature variation in the solution of the Reynolds equation with the intent of analyzing industrial bearing designs without requiring detailed temperature boundary conditions. The cross-film integrals found in the generalized Reynolds equation are evaluated for a quadratic variation in cross-film temperature. A closed-form solution for the viscosity variation across a simplified thin-film shows that a quadratic approximation of cross-film temperature is accurate. The cross-film integrals can be expressed using a multinomial power series and an incremental enhancement to previous approximate algorithms for the thermal analysis of fluid-film bearings. Application to a test rig bearing illustrates that the effect of considering cross-film viscosity variation, as opposed to a mean viscosity value based on the average cross-film temperature, generates changes in the predicted bearing characteristics where the journal temperature deviates from the average film temperature. Such a condition would be expected for a bearing with a thermal load coming from the associated process, whether from cooling or heating. With such an applied thermal load, several bearing characteristics showed an influence from the cross-film viscosity variation, including the operating attitude angle, required oil flow, peak film pressure, and stability threshold. Accurate consideration of shaft heat flux either into or out of a bearing requires inclusion of cross-film viscosity variation in the solution of the Reynolds equation.

Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998

KEY WORDS:

• Journal Bearings
• Lubricant Rheology
• Dynamic Modeling

Notes

Presented at the 53rd Annual Meeting in Detroit, Michigan May 17–21, 1998