Flow structure in the wake of a rotationally oscillating cylinder

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, Theta (A) and frequency ratio F-R=S/S-o where S is the forcing frequency and S-o is the natural frequency of vortex shedding. The ranges considered for these parameters are 40 less than or equal to Re less than or equal to 200, 0 less than or equal to Theta (A)less than or equal to pi and 0 less than or equal toF(R)less than or equal to2. 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].