Experiments with impulsive motion of a foil to generate large lift and thrust forces

Abstract

As underwater vehicles become increasingly versatile and capable, bio-inspired propulsion systems are becoming a viable possibility for future vehicles. In particular, flapping foil actuators are promising in their abilities for propulsion and maneuvering. Current underwater vehicles rely on propellers, which form a jet wake to produce propulsion forces, and, as such, experience an inherent delay between the movement of the propeller and the vehicle feeling a propulsive force. To mitigate this shortcoming, flapping foils were moved in swift, one-time strokes to produce large, transient forces in still water to produce propulsive and/or maneuvering forces almost instantaneously. Previous work produced trajectories, characterized by heave and pitch motions, for which the lift and thrust profiles were confirmed. These strokes take advantage of added mass/inertial effects to produce propulsive forces useful for maintaining position or orientation or for precise maneuverability. Various novel combinations of heave and pitch motions were tested and dye visualization was performed with a custom wing to elucidate the wake and vortical structures produced by these strokes.