FLOW TRANSITIONS IN THE WAKE OF A STREAMWISE-ROTATING SPHERE

The flow past a streamwise-rotating sphere is investigated numerically for Reynolds numbers (based on sphere diameter) in the range 10 < Re < 500, and dimensionless rotation speeds of 0 < Ω < 0.25. In particular, we focus on the influence of sphere rotation rates on the transition (or critical) Reynolds numbers. It is found that the transition to three-dimensionality occurs at a Reynolds number, Re1, which is highly dependent on the rotation rate. Furthermore, the transition to unsteadiness, which is characterized by the presence of hairpin vortex shedding, occurs at higher Reynolds numbers for intermediate rotation rates. An interesting characteristic of the flow is the appearance of “frozen ” vortex structures, which simply rotate in the wake without variation in shape or strength. These vortex structures are not observed for a stationary sphere