Ph.D. Thesis Defense by Susan R. Harp
Thursday, April 6, 2000

(Dr. Richard Salant, advisor)

"A Computational Method for Evalutating Cavitating Flow Between Rough Surfaces"

Abstract

The separation between lubricated, tribological surfaces is often on the same order as the surface roughness.  In such thin films, lubricant cavitation can be induced by a surface divergence on the order of the roughness.  The resulting “inter-asperity” cavitation significantly affects the performance of the tribological system.

In the current study, the Reynolds Equation is modified with flow factors to simulate the combined effects of surface roughness and inter-asperity cavitation.  The flow factors are functions of a cavitation number that characterizes the degree to which the fluid film has cavitated.  As in previous models, the flow factors are also functions of the ratio of mean film thickness to rms roughness and a surface directionality parameter.

The flow factors are determined in a parametric study via numerical experiments.  For each set of parameters, several statistically similar experiments are performed and the results averaged in order to calculate flow expectancies and mean pressure elevations.  The flow factor relations are organized into expressions that can be easily employed in the modified Reynolds equation for design purposes.

In order to extend its utility, the inter-asperity cavitation model is combined with a global cavitation model for situations in which both types of cavitation exist.  The model’s validity is proven through numerical experiments and the utility of the model is demonstrated in several examples of seal lubrication.