Effect of Helical Strakes Around a Finned Tube on Aeolian Tone

In the present paper, the characteristics of vortex shedding and Aeolian tone radiated from a finned tube with helical strakes were experimentally investigated. The helical strakes are mounted spirally around a serrated finned tube surface. We measured the turbulence intensity in the wake, velocity fluctuation spectrum, the coherence of velocity fluctuations in the spanwise direction and SPL spectrum. The Aeolian tone radiated from the finned tube with helical strakes at high Reynolds number was smaller than the case of no helical strakes. The helical stakes were effective to reduce the Aeolian tone radiated from the finned tube. And the existence of helical strakes of large diameter caused the decrease of the periodicity and the turbulence intensity in the wake of the finned tube. The coherent scale of Karman vortex in the spanwise direction is smaller than that of a finned tube without helical strakes. However, the effect of helical strakes of small diameter on vortex shedding depended on the Reynolds number. The Karman vortex was clearly formed even in the case of helical strakes of small diameter at low Reynolds number. The existence of helical strakes of small diameter around a finned tube caused the increase of the periodicity of vortex shedding from a finned tube. The coherent scale of Karman vortex in the spanwise direction was larger than that of a finned tube without helical strakes.