Feedback control of vortex shedding from a circular cylinder by cross-flow cylinder oscillations

Feedback control of vortex shedding from a circular cylinder in a uniform flow at moderate Reynolds numbers is studied experimentally with the cylinder subjected to feedback cylinder oscillations in cross-flow direction. The cylinder oscillation is digitally phase shifted with respect to the shedding vortex and is controlled by velocity feedback from the shear layer of the cylinder wake. Possible attenuation of vortex shedding is demonstrated by hot-wire measurements of the flow field and its mechanisms are studied by simultaneous data sampling and flow visualization with the smoke wire method and a laser-sheet illumination technique. Measurement results reveal substantial reduction in the fluctuating reference velocity at the optimum phase control. Flow visualization study indicates that the shear layer roll-up and the eventual vortex formation are dynamically attenuated under the control which results in a modification of the near wake.List of symbols A amplitude of cylinder oscillation - D cylinder diameter - E_u power spectrum function for fluctuating velocity u - frequency - R radius of circular cylinder - t time - u streamwise mean velocity - u streamwise fluctuating velocity - U streamwise mean velocity of main flow - u_r mean reference velocity - u_r fluctuating reference velocity - u_rf fluctuating reference velocity after filtering - y_c cylinder displacement - x, y, z coordinates from the cylinder center (Fig. 1) - feedback coefficient - phase lagThe authors would like to express thanks to Professor K. Nagaya for his advice for designing electromagnetic actuators in the present experiments.