Two-way Coupling between the Wake of a D-shaped Cylinder and a Thrust-producing Pitching Plate

For a cylinder in cross-flow, the phenomenon of vortex "lock-in" is the synchronization of vortex shedding with the vibration of a cylinder in the streamwise or transverse direction. On the other hand, an oscillating foil or fin immersed in the von Karman vortex street downstream of a cylinder can extract energy from the vortices, to reduce drag or enhance thrust, when the motion of the body is appropriately phased with the passing vortices. In the present study, the two-way coupling between a pitching plate and the vortex wake of a D-shaped cylinder is investigated under conditions in which the presence and motion of the plate influences the shedding behavior of the cylinder. The streamwise spacing between the cylinder and plate, as well as the pitching amplitude and frequency of the plate are systematically varied while visualizing the flow to understand how the motion of the plate influences vortex shedding from the cylinder and, subsequently, how the perturbed vortices interact with the plate. Measurements of the thrust and propulsive efficiency of the plate provide insight into how the fully-coupled system can be leveraged to maximize thrust performance of the plate under conditions in which it can modify the oncoming vortex street.