Drag Reduction of a Square Prism : 1st Report, Flow Control Around a Square Prism Using a Small Vortex shedder

Abstract

Experimental studies on drag reduction of a square prism were conducted. To control the flow around a square prism, a small vortex shedder was set up upstream of the prism. The side of the prism, D, was 30 mm and the Reynolds number was Re=3.2×10⁴. The diameter of the rod used as the vortex shedder, d, ranged from 1 to 6 mm, and the space between the prism and the rod, G, was varied. The results obtained are as follows. The critical space G_C, is given as G_C=D+4.5d, where vortex shedding from the rod disappears. The Strouhal number of the prism decreases at G>G_C and increases at G≤G_C. In the range of 0.1≤d/D≤0.2, drag of the prism decreases about 50% at G>G_C and 70% at G≤G_C.