Abstract
The effects of surface roughness on the molecular gas lubrication characteristics have been studied for defining the application limits of Molecular gas film lubrication (MGL) equation against the roughness. The applicability has been evaluated by comparing the difference of characteristics calculated by MGL equation and direct simulation Monte Carlo (DSMC) method. In this paper, the evaluation for the two kinds of surface roughness was performed to check the influence of roughness shape. The one of roughness has the sinusoidal shape and the other has the triangular shape. It comes evident that the magnitude of transverse flow velocity in the gas film has close relationship with the slope of surface roughness, by comparing the flow pattern for two roughness shapes. The transverse flow, which is not included in MGL equation, causes the difference between the calculated results obtained by MGL equation and DSMC method and, thus, the slope of surface roughness can be the index of applicability of MGL equation. It is clarified that the applicability declines in the case of large roughness slope. The roughness slope, which gives the limit of application, is large for smaller Knudsen number.
