Experiments on the reverse Bénard-von Kármán vortex street produced by a flapping foil

International audienceControl of wake vortices to generate propulsive forces is the everyday task of swimming fish and other animals. Many studies on actual flapping tails and fins have been motivated looking forward to gain a better understanding of this form of propulsion with the ultimate goal of enhancing man-made propulsive mechanisms. A feature that is present in almost every configuration involving flapping foils is the generation of a wake vortex street with the sign of vorticity in the core of each vortex reversed with respect to the Bénard-von Kármán (BvK) street in the wake of non-flapping body. The goal of the present work is to study experimentally this reverse BvK vortex street in a simple configuration in order to identify basic dynamical mechanisms