The effect of a perturbation on the flow over a bluff cylinder

Abstract
Measurements are presented of the frequency of vortex shedding from, in turn, a circular, a D-section cylinder, and a flat plate for a flow that has a single-frequency perturbation superimposed on its mean velocity component. It is found that over a range of velocities the vortex shedding locks-in to the frequency of the perturbation such that the shedding frequency is half the perturbation frequency. Also, the range of velocities for which lock-in occurs increases as the perturbation amplitude is increased. With lock-in, the mean base pressure is found to decrease, and measurements of the vortex shedding from the circular cylinder show that the correlation of vortex shedding increases. The changes associated with lock-in are found to be greatest for the circular cylinder.

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