Numerical investigation of a new three-degree-of-freedom motion trajectory on propulsion performance of flapping foils for UUVs

Abstract To improve the propulsive performance of unmanned underwater vehicles with flapping foils, a new three-degree-of-freedom motion trajectory for flapping foils named infinity-sign-motion “∞” is proposed in this study. The propulsive performances of the infinity-sign-motion are investigated and compared with that of other motion trajectories using computational fluid dynamics (CFD) based on the finite volume method (FVM). Two-dimensional unsteady incompressible Navier-Stokes simulations were conducted to investigate the fluid-foil interaction and determine the optimal parameters. The effects of the relative flapping frequency, the ratio of surging and heaving amplitude as well as the phase difference between surge and heave motion were systematically studied. Numerical results demonstrate that the hydrodynamic performance of the proposed “∞” motion is better than that of the other motions, and it can obtain more thrust force and higher propulsive efficiency. Specifically, the “∞” motion of flapping foils can generate three positive thrust peaks in one flapping cycle, while the other motions can only produce one or two positive thrust peaks. Moreover, the “∞” motion can achieve four times as much thrust force as that of the two-degree-of-freedom traditional motion, and the increase of propulsive efficiency is up to 29.47%.