Effects of Asymmetric Separated Shear Layers on the Vortex Shedding from a Circular Cylinder

Abstract

Experimental studies have been carried out to clarify the flow around a circular cylinder accompanying asymmetric separated shear layers. To control the flow, one or two tripping wires were attached on the surface of the cylinder. Three flow patterns were employed, that is, the laminar separation, turbulent separation and direct separation types. The flow behind the circular cylinder is dominated by the both separated shear layers. The Strouhal number behind the cylinder, the base pressure and the darg force acting on the cylinder become the intermediate values between those of the upper and the lower side flow patterns. In the case of asymmetric shear layers, the correlation between the Strouhal number and the drag force is the same as that of the symmetric ones. In the case of the turbulent shear layer from one side of the cylinder, the lift force of C_L=0.5∼0.8 is generated. The wake Strouhal number S^*_w/U_s(mean), defined by the mean velocity of the two shear layers U_s(mean) and the wake width at the position of vortex formation d_w, becomes almost a constant for various combinations of the flow patterns.