Flow Structure in the Wake of a Rotationally Oscillating Cylinder

Abstract

The characteristics of the flow in the wake of a circular cylinder performing rotational oscillation about its own axis and placed horizontally in a cross-stream is investigated. The governing equations based on stream function-vorticity formulation are solved numerically to determine the flow field structure. The parameters dominating flow structure are Reynolds number, Re, amplitude of oscillation, ΘA and frequency ratio FR=S/S0 where S is the forcing frequency and S0 is the natural frequency of vortex shedding. The ranges considered for these parameters are 40⩽Re⩽200, 0⩽ΘA⩽π and 0⩽FR⩽2. The lock-on phenomenon has been predicted and its effect on the flow hydrodynamics has been determined. The lock-on phenomenon is found to occur within a band of frequency encompassing the natural frequency. This band, however, becomes wider as the amplitude of oscillation increases. The obtained results show that the flow pattern in the near wake has a strong dependence on the oscillation parameters but not the far wake. [S0098-2202(00)01102-0]