Dynamics of a hydrofoil in the wake of a cylinder

We present the dynamics of a hydrofoil free to oscillate in a plane as it interacts with vortices that are shed from a cylinder placed upstream. When the cylinder is fixed, the shedding of vortices follows the Strouhal law, and the hydrofoil responds by following several different trajectories in all of which oscillations in the transverse direction follow the frequency predicted by the Strouhal law. When the cylinder is forced to rotate in one direction, at higher rotation rates, the shedding of vortices is suppressed, and the cylinder exhibits a mainly static response. When the cylinder is forced to rotate periodically, the frequency of the hydrofoil’s response in the transverse direction follows the frequency of the forced rotation rather than following the shedding frequency predicted by the Strouhal law. Based on these observations, we discuss methods of controlling the rotation of the cylinder such that we can obtain a predetermined trajectory for the hydrofoil’s response.