A STUDY ON VORTEX SHEDDING FROM SPHERES IN A UNIFORM-FLOW

Vortex shedding from spheres at Reynolds numbers from 3 x 10(2) to 4 x 10(4) in a uniform flow was investigated experimentally. Standard hot-wire technique were used to measure the vortex shedding frequency from spheres in a low-speed wind tunnel. Flow-visualization experiments were carried out in a water channel. Important results from the investigation were that (i) the variation of the Strouhal number St ( = fD/U0, U0: freestream velocity, D: diameter of the sphere, f: vortex shedding frequency) with the Reynolds number ( = U0D/v, v: kinematic viscosity) can be classified into four regions, (ii) the Reynolds number at which the hairpinshaped vortices begin to change from laminar to turbulent vortices so that the wake structure behind the sphere is not shown clearly when a Reynolds number of about 800 is reached, and (vi) at Reynolds numbers ranging from 8 x 10(2) to 1.5 x 10(4), the higher and lower frequency modes of the Strouhal number coexist.