Experimental and numerical study on a uniform shear flow past a circular cylinder

Abstract

Extensive laboratory experiments and numerical studies were carried out to investigate the uniform-shear flow approaching a circular cylinder. The impact of the free-stream shear on the vortex shedding frequency, force coefficients and wake structure is to be examined. A water tunnel was constructed, and a non-intrusive measurement system was devised to observe the wake pattern behind the cylinder. The aim of the present experiment is to construct the Strouhal number(St)-Reynolds number(Re) diagrams over a broad range of the shear parameter Sk (0 $\le \mbox{Sk} \le 0.25$) and at higher values of Re($600 \le \mbox{Re} \le 1600$). An individually controlled multi-channel shear flow regulator was installed in the water channel. This proved to be capable of generating high-quality uniform-shear flows. An image processing technique, in conjunction with flow visualization studies, was used to secure quantitative depictions of vortex shedding from the cylinder. Parallel numerical studies were made to complement the experimental results. The vorticity stream-function formulation was adopted to numerically solve the Navier-Stokes equations. The far-field boundary conditions were obtained based on the integral series formula. The results of numerical computaions were consistent with the experimental observations. The three-dimensionality of the flow was weak under the operating conditions of the present experiment. The St-Re plots obtained for low Reynolds numbers were compatible with the existing data in the literature. The present results indicate that St tends to be fairly constant with Re at large Reynolds numbers. The Strouhal number increases with increasing shear parameter. Measurements were made of the drag coefficient $\mbox{C_d}$ by means of a force-transducer. The drag coefficient decreases with increasing Re; also, $\mbox{C_d}$ decreases as the shear parameter Sk increases at high Reynolds numbers.