Flows over a spinning disc at incidence

Flows normal to the surface of stationary finite discs exhibit distinct periodic motions in their wakes marked by regular shedding of loop-like vortical structures. Most studies focus on the flows in the wake region; however, the present study focuses on the flows upstream and near the surface of spinning discs at incidence.  Flows are studied over a range of angles of incidence, 0 ≤ α ≤ 36^◦, spinning at angular velocities, Ω = 0 & ± 6.2 rev/s, in a freestream velocity of U_∞ = 2 m/s. The Reynolds number based on the diameter of the disc is 2.7 × 10⁴. A smoke-wire technique is used for smoke visualization and a planar particle image velocimetry technique is used to make velocity measurements near the upstream surface.

The formation and shedding of coherent vortical structures are observed near the upstream surface of the disc over the full range of angle of incidence. Two vortex shedding modes are observed, though signatures of both modes are present over the full range of angle of incidence. The primary mode is more prevalent at low angles of incidence and the secondary at high angles. The flows over spinning discs generally mimic flows over nonspinning discs, but resulting centrifugal forces affect vortex formation and decay. Time averaged velocity measurements provide axial and radial velocity profiles that are compared to existing analytic solutions.