On the flow generated on the leeward face of a rotating flat plate

We experimentally investigate the flow generated on the leeward face of a rotating trapezoidal flat plate of low-aspect-ratio; the motion is an advancing stroke from rest at 90° angle of attack with Reynolds numbers of O(103). The objectives are to characterize the fluid velocity near the tip of the plate for different plate kinematics. The experiments are conducted in a water tank facility, and digital particle image velocimetry is performed to obtain planar velocity measurements. The flow in the region near the tip is relatively insensitive to Reynolds number over the range studied. The component normal to the plate is unaffected by total rotational amplitude, while the tangential component has dependence on this angle. Also, an estimate of the first tip vortex pinch-off time is obtained from the near-tip velocity data and agrees very well with values estimated using circulation. The angle of incidence of the bulk root-to-tip flow relative to the plate normal becomes more oblique with increasing rotational amplitude. Accordingly, the peak magnitude of the tangential velocity is also increased and as a result advects fluid momentum away from the plate at a higher rate. The more oblique impingement of the root-to-tip flow for increasing rotational amplitude is shown to have a distinct effect on the associated fluid dynamic force normal to the plate. For impulsive plate deceleration the time that a nonnegligible force exists decreases, while for nonimpulsive plate deceleration both this time and the relative force magnitude decrease for larger rotational amplitudes.