Propulsive Performance of a Twin-Rectangular-Foil Propulsor in a Counterphase Oscillation

Analysis of propulsive thrust and efficiency of a finite aspect ratio, twin-foil counter- phase wing-in-ground (WIG) effect propulsor configuration is made using a time- domain panel method. Comparisons were made for the effects of number of foils (single versus double), aspect ratio, variable distance between two foils with fixed heave amplitude—that is, influence of interaction, and heave amplitude with fixed distance. In addition to the apparent advantage of propulsor dynamics equilibrium due to the cancellation of the side and vertical forces, results show that each foil of the twin-foil configuration, when close to each other to generate the WIG effect, has substantially higher thrust contribution than the single-foil propulsor under moderate to heavy load conditions (reduced frequency greater than 0.5). Due to the interaction of foils on each other, increase of thrust also produced a higher efficiency over the whole range of reduced frequencies examined. Findings also include the tendency of the thrust and efficiency due to both the fixed heave amplitude with varied distance between foil equilibrium position and fixed distance with varied heave amplitude. Twin-foil counterphase oscillating propulsors show an aerodynamic and hydrodynamic advantage for micro air vehicles (MAV) and autonomous underwater vehicles (AUV) over the single-foil configuration.