カルマン渦放出に及ぼすフィンと螺旋状側板の効果に関する研究(J13-8 渦励振II,J13 流体関連の騒音と振動)

Abstract

The purpose of this paper is to clarify the effects of fin and helical strakes around a circular cylinder on the vortex shedding. The periodic phenomena of velocity fluctuation in the near wake of a circular cylinder with fin and helical strakes were experimentally investigated by using hot-wire sensors. The distributions of the mean velocity, the intensity of velocity fluctuation and its-spectrum were measured as well as the coherence of a shedding vortex in the spanwise direction.-As a result it was made clear that Karman vortex was clearly formed even in the case of a circular cylinder with fin. The existence of fin around a circular cylinder caused the decrease of the vortex shedding frequency. On the other hand, the velocity fluctuation and the periodicity of vortex shedding from a circular cylinder with helical strake became weak. The coherent scale of vortex in the spanwise direction in the case of helical strakes is much smaller than that of circular cylinder. However, the coherent scale in the case with fin was larger compared with that of circular cylinder.