Abstract
This paper describes an experimental investigation on the blockage effect of an upper wall of wind-tunnel on the flow past sphere placed on a ground plane. The experiment was carried out in an N. P. L. blow down type wind-tunnel having a working section of 400mm×400mm×2, 000mm in size at the Reynolds number Re=4.72×104. The surface pressure distribution on a sphere, the frequency of arch vortices shedding from sphere and the length of recirculation region were measured, and the drag and lift coefficients were determined by integration of surface pressure. The experimental results were discussed in comparison with the corrected results by the existing formulae. From those results, it was found that the drag and lift of the sphere increase as the blockage ratio (S/C) increases, and that the critical value of blockage ratio of wind-tunnel wall which can be ignored, is S/C=0.05.
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