EFFECT OF THE SECONDARY FLOW ON KARMAN VORTEX SHEDDING FROM A YAWED CYLINDER.

Abstract

The Karman vortex shedding from a circular cylinder with a yaw angle in a uniform flow was investigated using a wind tunnel. The yaw angle made the vortex shedding irregular and its frequency low. In addition, an intense secondary flow along the cylinder generatrix in the wake just behind the cylinder was induced by the yawing. When a pair of parallel plates were placed parallel to the free flow behind the cylinder in order to cut off the secondary flow, the vortex shedding in the area between the plates became regular and the frequency returned to the value for a normal one. The vortex shedding was more regular when the distance between the plates was made smaller, whereas the highest frequency was attained when the distance was 1 approx. 1. 6 times the cylinder diameter. It is concluded that the depression of the vortex shedding frequency by the yawing is attributed to the secondary flow behind the cylinder.