Thrust and Efficiency of Propulsion by Oscillating Foils

Oscillating foils are being considered for propulsion of submersible vehicles and micro air vehicles (MAVs), at low Reynolds numbers where conventional propulsion techniques become inefficient. Linearized theories and potential flow methods provide good estimates of thrust and propulsive efficiencies at higher Reynolds numbers, but cannot account for the leading-edge flow separation and vortex formation that can occur in viscous flows. A 2D unsteady Navier Stokes solver was used to explore the effect of flow separation on the thrust and efficiency of an airfoil undergoing various combinations of sinusoidal pitching and plunging motions. The Navier Stokes solver has been validated against a number of flow visualizations for pure plunging motion, and quantitative experimental and computational studies of pure pitching motion, with good results [1]. Here combined pitching and plunging motions are computed, with thrust and efficiency results compared to small-amplitude potential theory (Garrick [2]), largeamplitude unsteady panel method (UPM) potential flow simulations [1, 3], and experimental results of Anderson et al [4].