Experimental and computational study of lift - Based flapping foil propulsion for ships

Flying and marine animals often use flapping wings, fins, or tails to generate thrust. This was based on law of action and reaction because a force given by swimming animals to a fluid causes a reacting force from the fluid to animals, namely thrust. The entire sub-sea aquatic propulsion modes are classified into four different forms: Lift - based, Drag - Based, Undulation mode and Jet Propulsion. Fluid dynamics related to thrust of swimming animals was discussed. In this paper, we used lift-based propulsion modes for 3m ship model. The reciprocating motion consists of yawing and swaying. In this study, the concept design of flapping foil propulsion boat is done with reference to penguin or turtle propulsion. Resistance tests are carried out in towing tank with hull and fins attached to bottom of ship model. The efficiency of lift - based bio-mimetic flapping foil propulsion system is presented in this paper. Numerical simulations have been carried out in CFD Package Ansys Fluent to analyze the vortices of flapping foils. We have studied the thrust generation by a dual flapping foils in tandem mode and the results are presented here. The staggered array of vortices that forms in the wake of a cylinder (or any bluff body) is von karman vortex street (vks) which is drag. At low flapping amplitude for a fixed strouhal number a forced wake resembling a von karman vortex street. When the amplitude increases the rotation of direction of vortices changes and the flows in the wake transit from von karman (vks) to reverse von karman (rvks) and the mean flow is a typical jet profile which characterizes thrust.