Wake of rotating and translating sphere at low Reynolds number

The aim of this paper is to experimentally investigate the wake of a transversely rotated sphere at Reynolds number (Re), ranging from 250 to 400, for nondimensional rotational speed, Ω* of 0.375 and 0.5. Nondimensional rotational speed, Ω*, is defined as the ratio of maximum azimuthal velocity and free stream velocity of the sphere. PIV measurements show that flow exhibits the presence of strong shear on the upper surface at Ω*= 0.375 and Re=250 and with increase in rotational speed there is decrease in separation bubble on bottom surface. Velocity profiles for steady case at different sections in spanwise direction shows self-similarity. Vortex ring generated due to three dimensional separations from the surface of the sphere becomes unstable with small perturbations. At similar Reynolds number, but Ω*= 0.5 separated shear layer becomes unstable and shear layer breaks down into vortex rings and the phenomena repeat with time. This regime is termed as vortex shedding. The strength of the vortex rings weakens in the far wake with time. Time period of the vortex shedding remains nearly constant in the given Ω* and Re. The Strouhal number calculated in this range of Ω* and Re compares well with the reported literature.