A Numerical Analysis of Flow around Rectangular Cylinders

Abstract

By the finite difference method, flows around cylinders with rectangular cross sections of various width-to-height ratios of 0.4 to 8 have been computed in the range of Reynolds numbers from 100 to 1.2×10³. We have successfully simulated some interesting phenomena whereby a flow around the cylinder with a B/H ratio of 2 is fully separated from the leading edges at the Reynolds number of 800, while for the cylinder with a B/H ratio of 2.8, a fully separated flow changes to an alternate reattachment flow with lapse of time at the Reynolds number of 1.2×10³, and two components with different Strouhal frequencies appear in a flow field around the cylinder with the B/H ratio of 6 at the Reynolds number of 800. Namely, the flow pattern critically changes when the B/H ratio is 2.8 and 6 at Reynolds numbers of 500 to 1.2×10³. It is clarified by the numerical simulation that the component with a high Strouhal frequency is induced by the vortices separated from the trailing edges and that the low Strouhal component is due to the oscillation of flow over the side surfaces accompanied by the movement of separation bubbles. Finally, the computed results of flow patterns, base pressure, drag force and Strouhal number show a good agreement with the experimental results.