Swimming Freely Near the Ground*

A free-swimming potential flow analysis of unsteady ground effect is conducted for two-dimensional airfoils via a method of images. The foils undergo a pure pitching motion about their leading edge, and the positions of the body in the streamwise and cross-stream directions are determined by the equations of motion of the body. It is shown that the unconstrained swimmer is attracted to a time-averaged position that is mediated by the flow interaction with the ground. The location of this fluid-mediated equilibrium position is probed by varying the non-dimensional mass, initial conditions and kinematic parameters of motion. Comparisons to experimental data are also made to pinpoint the effects viscosity, leading edge separation, and unconstrained motion have on wake structures and the fluid-mediated forces. The benefits incurred from the solid boundary are extracted by normalizing propulsive metrics by performance data exhibited by isolated swimmers with identical kinematics.