Manipulating thrust wakes: A parallel with biomimetic propulsion

We present an experiment to investigate the role of shed vortices in thrust production. Using two different mechanisms, harmonic acoustic forcing and vortex trapping, a dry-air jet was manipulated to give the wake a typical propulsive-like pattern as observed behind swimmers or flyers. Our results show that even in a thrust production configuration, wakes with asymmetric roll-up of vortices are always associated to performance loss. By contrast, cases involving symmetric modes show thrust enhancement, as reported in very recent studies on pulsed jet propulsion.