Impact of the surface roughness on the net lift of a compressible slider including the effect of wear

Abstract

Abstract The paper deals with the impact of surface roughness on the net lift of a compressible slider. The problem appears for gas seals and aerodynamic bearings operating at very low film thickness during start-up and shutdown. By using a Weibull distribution of the thin film heights, the influence of the surface roughness is tackled by analyzing the impact of its standard deviation, of its autocorrelation length and of its shape parameter. This latter enables to simulate new and worn surfaces. The analysis is statistically performed by reporting average values and standard deviations for all values of the net lift force. Both an inclined and a parallel rough slider are analyzed. The results show that the compressible thin film flow between two very closely spaced surfaces (convergent or parallel) can generate a net lift that increases with the standard deviation of the combined roughness and decreases for worn surfaces. The lift effect is explained by the high compressibility of the lubricant (air in this case) which generates higher pressures than the under-pressures with respect to the ambient level.