A Numerical Analysis of Flow around Rectangular Cylinders

Abstract

By a 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 of l00 to 1200. We have successfully simulated some interesting phenomena whereby flow around the cylinder of the B/H ratio of 2 changes to a fully separated flow at a Reynolds number of 800, while for the cylinder of the B/H ratio of 2.8, a fully separated flow changes to an alternate reattachment one at a Reynolds number of 1200 with the lapse of time, two components with different Strouhal frequencies appear in a flow field around the cylinder of the B/H ratio of 6 at a Reynolds number of 800, and the flow pattern critically changes when the B/H ratio is 2.8 and 6 at Reynolds numbers of 500 to 1200. It is clarified by a numerical simulation that the component with a high Strouhal frequency is induced by vortices separated from the trailing edges and that the low Strouhal component is due to the oscillation of flow over the side walls accompanied by a movement of separation bubbles. Finally, the computed results of flow patterns, base pressure, drag force and Strouhal number show a good agreement with the experiments.