Effect of Reynolds number in transversely rotating and translating sphere

Here we present 2D Particle Image Velocimetry results of flow in the wake of a transversely rotating and translating sphere in quiescent water in wide range of Reynolds number (Re). A roller connects the sphere by a small shaft and assembly moves on a track that is capable of changing the angle of inclination resulting in different velocity of the sphere. For rotation rate of 0.375 (ratio of maximum sphere velocity to free stream velocity) different regimes of wake structures are seen when Re is varied from 250 to 1750. At Re of 250 flow remains steady with strong shear present in the wake. The 2D velocity field shows asymmetry in the velocity field arising due to rotation. With increase in Re to 267 the shear layer becomes unstable and pair of vortices appears in the wake. Vortex shedding continues with the increase in Re. At Re=1500, wake is combination of shear layer vortex (near wake) and vortex shedding (far wake). At Re of 1750 shear layer type of shedding dominates. Possibly this is a 2D representation of  hairpin type of vortex in the mid-plane. The velocity profile in the wake at steady as well as in regular vortex shedding regime shows some self-similarity. Self-similarity is destroyed at higher Re due to formation of small-scale structures from the shed vortex rings.