| Summary: | Molecular gas film lubrication (MGL) equation, which is derived based on linearized Boltzmann equation, is the reliable means to analyze the molecular gas flow in the narrow channel, whose thickness is as thin as the molecular mean free pass. Though, the application limit of MGL equation against the surface roughness exists. Because the equation is available under the condition that the local surface curvature is sufficiently large, as in the case of Reynolds equation. This paper describes the effects of surface roughness on the lubrication characteristic and the application limit of MGL equation. The lubrication characteristics affected by surface roughness, such as the pressure, the shear force and the mass flow rate, are calculated by using two methods, direct simulation Monte Carlo (DSMC) method and MGL equation. DSMC method is free from the restriction by surface configuration and is expected to give the correct solution for molecular flow. The calculations are performed against the simple two-dimensional channel, which consists of the moving smooth plate and the stationary flat slider possessing the triangular roughness. No pressure difference exists between the ends of slider. It is clarified that the difference of resulted characteristics by two methods expands as the roughness slope increases, indicating the application limit of MGL equation. It is suggested that the relation between the mass flow rate and the roughness slope could be the index of the application limit of MGL equation.
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