Free Swimming Bio-Inspired Hydrofoils in Unsteady Ground Effect

A free-swimming potential flow analysis of unsteady ground effect is conductedfor self-propelled, two-dimensional hydrofoils via a method of images. The foilsundergo a pure pitching motion about their leading edge, and the positionsof the body in the stream-wise and cross-stream directions are determinedby the equations of motion of the body. It is shown that the unconstrainedswimmer is attracted to a time-averaged position that is mediated by the flowinteraction with the ground. The robustness of this fluid-mediated equilibriumposition is probed by varying the non-dimensional mass, initial conditionsand kinematic parameters of motion. Comparisons to the foils fixed-motioncounterpart are also made to pinpoint the effect that free swimming nearthe ground has on wake structures and the fluid-mediated forces over time.Optimal swimming regimes for near-boundary swimming are then determinedand elaborated upon.