Numerical Study of Film Thickness Averaging in Compressible Lubricating Films Incurring Stationary Surface Roughness

Abstract

The compressibility effects of lubricating films incurring a roughness on film thickness averaging were studied numerically with a focus on the physical interpretation of the roughness effects. A numerical comparison between load-carrying capacities resulting from rough film thickness and from averaged film thickness are presented for a wide range of bearing numbers up to 107 . It is found that currently indicated particular features such as the appearance of the maximum or minimum load-carrying capacity can be induced from the superimposition of local compressibility effects (LCEs) caused by individual unit roughness on compressibility effects owing to averaged film thickness. The most noticeable difference between the case of small LCEs and that of saturated LCEs is that the roughness phase results in a minimal effect with the increasing wave number for the former, while it creates a dominant effect for the latter. The results confirm that the same averaging method as that for incompressible films can be applied for small LCEs, and that Greengard’s method is applicable for nearly saturated LCEs. It should be noted that the averaged film thickness can be determined physically for small LCE regions, while it is defined mathematically for nearly saturated LCE regions.