Surface Roughness Effects in Low Reynolds Number Channel Flows (Preprint)

Rarefied helium and nitrogen flow expanding into vacuum through 150μm high and 1.5 cm long channels is studied experimentally and numerically with the DSMC method. Different types of channel walls are examined, both polished and rough with well characterized roughness shaped as triangles and rectangles. The pressure varies from 200 to 13,000 Pa, with the gas mean free path being both much larger and much smaller than the roughness size of about 20μm. A conical surface roughness model applicable for the DSMC method is proposed. An expression relating this model to the Cercignani-Lampis scattering model is derived. Good agreement between the numerical and experimental results is observed for the rough walled channel.