Self-propulsion of a Flexible Plunging Foil Near a Solid Wall

This paper is a numerical investigation of wall effect on the self-propulsion of a flexible plunging foil. Simulations are performed by a Fluid-Structure Interaction (FSI) solver which couples immersed boundary method for the fluid and finite difference method for the structure. A systematic study is conducted by varying the distance between the foil and the wall. It is found that the time-averaged lift force first pulls the foil towards the wall and then pushes foil away from the wall as the distance decreases. The cruising speed increases when the foil approaches the wall, while the propulsive efficiency decreases a little and then increases rapidly as the distance becomes less than one chord length of the foil. It is observed that wake structure deflects obviously in the near-foil regions, but becomes parallel to the horizontal direction again in the far field downstream.