RANS Simulations of Oscillating Foils for High-Thrust Marine Propulsion

Flow simulations were performed at a high Reynolds number (10⁶) for oscillating foil propulsion over a sweep of pitch, heave and frequency kinematics. The goals are to investigate thrust and efficiency values over the parameter range for bio-inspired propulsion on larger surface vessels such as tug boats and other watercraft. An incompressible RANS solver was used on a two-dimensional domain with dynamic meshing. Results show high efficiencies up to 80% for low frequencies and angles of attack, whereas high thrust coefficient values were obtained at higher frequencies. Further calculations indicated performance comparable to conventional propellers, but with an ability to adapt the kinematics to meet vessel demands in different operational regimes. Contour plots of efficiency and thrust coefficient in terms of Strouhal number and max relative angle of attack provide an insight into modulating the kinematics of the heaving-pitching motion from a high-thrust regime to a high-efficiency regime. Lastly, flow around the hydrofoil and in the wake is classified into different regimes based on nature of flow separation and formation of vortices, demonstrating the effect of hydrodynamics on performance.