Influence of Cross-Sectional Configuration on Karman Vortex Excitation

Abstract

The influence of cross-sectional configuration on Karman vortex excitation was investigated experimentally using a circular, a semi-circular and a triangular cylinder with an equal height. The cylinders were supported elastically in a wind tunnel for a cross-flow oscillation test, with virtually equal effective mass, spring constant and damping factor. Although the "lock-in" of Karman vortex shedding has been confirmed to occur on all three cylinders when a certain oscillation amplitude and frequency are given, the Karman vortex excitation behavior of the elastically supported systems differs drastically among the three cylinders. The mechanism for the effect of the cross-sectional configuration on the Karman vortex excitation is attributed to the movement of the separation point. In the case of the circular cylinder, the separation point moves forward and backward around the maximum height position synchronizing with the cylinder oscillation, thus the alternating lift force becomes higher. On the other hand, movement of the separation point is limited to the upstream arc for the semicircular cylinder and fixed at the downstream edge for the triangular cylinder.