Vortex shedding in unsteady flow

Previous experiments by other workers have shown that when a cylinder vibrates in a steady flow the frequency of the vortex shedding from the cylinder can synchronize with the frequency of the cylinder's vibration. As a result the shedding frequency remains constant over a range of flow velocities, and the oscillatory forces acting on the cylinder increase. It has been suggested that synchronization should also occur for a stationary cylinder in a flow which has a superimposed oscillatory perturbation. An experimental investigation was made, therefore, of the vortex shedding from rectangular and circular cylinders in such a flow. Synchronization of the frequency of the vortex shedding from a circular cylinder with the perturbation frequency was found when the vortex shedding frequency was half the perturbation frequency. This result confirms the prediction by Clements (1975). The flow is similar to that which occurs in water when waves are superimposed on a steady current. That synchronization can occur for this type of flow could be important in the design of certain offshore structures. © 1983.