Subsonic Rarefied Gas Flow over a Rectangular Cylinder

A subsonic rarefied gas flow past a rectangular cylinder of infinite span is studied by applying a numerical method based on the solution of the S-model kinetic equation. The effect exerted on the resulting flow field by the Reynolds number Re∞ ranging from 10 to 200 is analyzed. At Re∞ = 200 the effect of the cylinder geometry on the flow field is investigated by varying the aspect ratio AR of the cylinder from 1 to 8. The results are presented in terms of the drag, lift, and pressure coefficients and the Strouhal number. The flow patterns downstream of the cylinder exhibit a recirculation region whose size and shape depend on both Re∞ and AR. In the case of steady flow, it is found that the flow-characterizing coefficients depend strongly on the Reynolds number. In the case of unsteady flow, this dependence becomes weaker. As AR increases, the recirculation region downstream of the cylinder is reduced, which leads to a decrease in the drag coefficient. Additionally, the reliability of the approach applied to a class of similar problems is estimated by comparing the present results with data available in the literature.