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[FAQ]

Studies have shown that for Re < 20 (Re based on sphere diameter), there is no separation and the flow is referred to as creeping flow. Taneda's paper determined that separation from the rear of the sphere occurs at Re ~ 24 and results in the generation of an axisymmetric vortex ring. At Reynolds numbers between 24 and approximately 210, the flow is separated, steady, axisymmetric and topologically similar. In the range of 210 < Re <270, the flow becomes non-axisymmetric as the ring-vortex shifts, however this wake was observed to remain steady. For Re > 280, hairpin-shaped vortices are periodically shed from the sphere to form a completely laminar wake. Hence, up to Re=210, one can model the flow over sphere as axisymmetric.