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 $\operatorname{Re}_\infty$ ranging from 10 to 200 is analyzed. At $\operatorname{Re}_\infty$ = 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 $\operatorname{Re}_\infty$ 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.