Flow behavior behind a clockwise-and-counterclockwise rotational oscillating cylinder

Flow characteristics downstream of a rotational oscillating cylinder at Reynolds number Re = 300 was investigated. The experiments were conducted using a model cylinder in a recirculating open water channel and the flow field was captured by using the Particle Image Velocimetry (PIV) technique. The model cylinder was set to undergo clockwise-and-counterclockwise rotation at selected angular amplitude (angular amplitude α varying from 0° to 360°) and at the lock-on frequency ratio Fr = 1.0 (where Fr = fn/fv, the ratio of the forcing frequency fn to the natural vortex shedding frequency fv). The effects of rotational movement of the cylinder on the near wake downstream of the cylinder were interpreted in terms of the instantaneous vorticity patterns, as well as the time-averaged streamline topology, mean velocity distributions and Reynolds shear stress contours. Based on the observation of the flow patterns and vortex contours, it was deduced that the clockwise-and-counterclockwise rotation produced significant effect on the wake and modified the wake flow structures and vortex shedding patterns. The time-averaged streamline structures appeared to be non-symmetrical about the longitudinal axis of the flow.