A simple model of propulsive oscillating foils

The design of thrusters inspired by the locomotion of fishes is currently investigated in many research centres for unmanned underwater vehicles. Fast fishes propel themselves in water through the rhytmic motion of their tail. Propulsion is achieved by means of the periodic shedding of vortex structures by the edges of the tail. Thrust is produced because the vortices give rise to a steady jet of fluid which leaves the tail in the direction which is opposite the forward motion of the fish. Assuming that the fish tail can be modelled by a 2-D plate in steady forward motion and oscillating with a combination of harmonic heaving and pitching movements, Brown and Michael's model is presently used to determine the dynamics of the vortex structures shed by plate edges. Numerical simulations have been carried out to investigate the effects on the flow field of varying the physical parameters of the phenomenon. The knowledge of the strength and trajectory of the vortex structures shed by the plate allows the characteristics of the jet producing the thrust to be quantified.