Review of flapping foil actuation and testing of impulsive motions for large, transient lift and thrust profiles

Abstract

Flapping foils were tested to produce large, transient forces in still water. These swift, onetime strokes take advantage of added mass/inertial effects and large, stably attached vortices to avoid delay due to the realization of a jet wake for propulsion [1]. Previous work has produced trajectories, characterized by heave and pitch, for which the lift and thrust profiles were confirmed. Two trajectories were reproductions from previous studies, and the lift and thrust force profiles match those produced before. An additional trajectory was tested, which produced a much different profile. All three trajectories included a smooth sweeping motion, but the third trajectory included a subsequent sharp change in pitch. This sharp change in pitch, or pure rotation, produced sharp force peaks and oscillations in thrust, in addition to force peaks from the sweeping motion which resembled the other two trajectories' profiles. Further work includes confirming the lift and thrust coefficients and exploring additional trajectories or optimizing current trajectories for producing large, transient forces for underwater vehicle propulsion and control.