Vortex Structure and Periodicity of Disturbances in the Wake of a Rotationally Oscillating Cylinder

抄録

The onset of periodic behavior in a two-dimensional unsteady flow past a rotationally oscillating circular cylinder is examined numerically by the finite-element method. The main emphasis is placed on the wake–cylinder response for the high oscillation frequency. The frequency responses are examined by measuring the power spectra of the lift coefficient. It is shown that rotary oscillations produce a coupled wake–cylinder response. The power spectra of the lift coefficient associated with these coupled motions have dominant peaks which are combinations of multiples of the shedding frequency and the forcing frequency. Instantaneous vorticity contours are also displayed to show the near-wake flow structure subjected to the controlled forcing.