A Study on Vortex Shedding from Spheres in a Uniform Flow

Vortex shedding from spheres at Reynolds numbers from 3×102 to 6×104 in a uniform flow was experimentally investigated. Standard hot-wire techniques were used to measure the vortex shedding frequency form spheres in a low-speed wind tunnel. Flow-visualization experiments were carried out in a water channel. Important findings resulting from the investigation were that (i) the variation of the Strouhal number St (=fD/U0, U0 : free-stream velocity, D : diameter of sphere, f : vortex shedding frequency) with the Reynolds number Re (=U0D/ν, ν : kinematic viscosity) can be classified into four regions, (ii) the critical Reynolds number at which the horseshoe-shaped vortex loops are shed periodically is about 300, (iii) the vortex loops diffuse very rapidly and the wake structure of the sphere is not shown clearly when a Reynolds number of about 800 is reached, and (iv) at Reynolds numbers ranging from 8×102 to 1.5×104, the higher and lower frequency modes of the Strouhal number which are caused by the periodic fluctuation in the vortex sheet separating from the surface of the sphere and in a wake with progressive wave motion are coexisted.