Performance of flapping foil propulsion

The performance of an aquatic propulsion system inspired from the thunniform swimming mode is experimentally studied. This consists of generating the propulsive force with a foil undergoing a harmonic flapping which is a combination of a heave translation and a pitch rotation. Experiments are performed at a fixed value of the Reynolds number and of the heave amplitude. The effects of variations of the Strouhal number and of the maximum angle of attack on the thrust force and on the hydromechanical efficiency are investigated. Systematic measurements of the fluid loading show a peak of efficiency of more than 70% for optimal combinations of the parameters. Moreover, a parameter range is identified where efficiency and high thrust conditions are achieved together, as required for use as a propulsion system. When performing experiments on foils undergoing nonsymmetrical flapping, we also observe the maneuvering capacity of such a biomimetic system.