Experimental study of flapping foil propulsion system for ships and underwater vehicles and PIV study of caudal fin propulsors

Deep sea aquatic animal propulsors are classified into four main categories lift-based propulsion, drag-based propulsion, undualtion mode and jet propulsion. In order to develop combined flapping and undulation mode propulsion for ships and underwater vehicles a brief introduction is given to lift-based propulsors and undulation mode. Combined bio-mimetic flapping and undulation mode propulsion systems for underwater vehicles have advantages such as ecologically pure, relatively low operational frequency and higher efficiency. This system can combine the function of propulsor, control device and stabilizer, provides static thrust, high maneuverability, less conspicuous wake and less cavitation problem than conventional propellers. In this paper, we experimentally study the application of a lift-based fore flipper locomotion applied to a 3m ship model, the concept of which resembles to the propulsion of penguins and turtles and present the results and observations. An electro-mechanical drive and transmission system is designed to actuate a pair of oscillating foils fitted at the bottom of the ship model. The model performances, both resistance and propulsion aspects, were studied. Sharks exhibit high-performance aquatic locomotion through oscillation of its homocercal forked caudal fin. This paper also presents the PIV measurements carried out on a live shark fish to understand and analyze the hydrodynamic behavior of its propulsion using the caudal fin. The velocity vector plots shows that the fins and caudal fins produce reverse von Karman vortex street resulting in a aftward jet formation which gives it the propulsive force.