Multiscale hydrodynamics in thrust bearing involving surface roughness

When the surface roughness is comparable to the surface separation in a hydrodynamic thrust bearing, the effect of the surface roughness should be considered. In the condition of low bearing clearances such as on the scales of 1 nm and 10 nm, normally not only the surface roughness but also the physically adsorbed layer on the bearing surface should be simultaneously considered in evaluating the bearing performance. The present paper presents the numerical calculation results of the surface roughness influences on the hydrodynamic pressure and carried load of the inclined fixed pad thrust bearing with low bearing clearances when the effect of the adsorbed layer is incorporated. It is shown that the influence of the surface roughness is strongly dependent on the adsorbed layer and it is significantly increased with the increase in the interaction strength between the fluid and the bearing surface when the bearing clearance is low. For a weak fluid-bearing surface interaction, the results are close to those obtained from the classical hydrodynamic theory indicating the increase in the hydrodynamic pressure and carried load of the bearing with the increase in the surface roughness, while for the medium or strong fluid-bearing surface interactions, this surface roughness effect is much stronger. The results reveal the new mechanism in the studied model of the bearing regarding the coupled effects of the surface roughness and the physically adsorbed layer on the bearing surface.