Hydrodynamic and energy extraction properties of oscillating hydrofoils with a trailing edge flap

In order to improve the energy extraction efficiency of the oscillating hydrofoil, this research proposes a model of an oscillating hydrofoil with trailing edge flaps. In this study, firstly we established the equation of the flap swing motion equation and that of the effective angle of attack angle, then the model of simple oscillating hydrofoil structure was numerically simulated using the dynamic and moving grid technology of the CFD software. Secondly, the model of oscillating hydrofoil structure was modified with trailing edge flap and the model was numerically simulated with dynamic and mobile grid technology of CFD software with refined the equations of motion and the equation of effective attack angle of flap swinging. The simulation results show that the length, the pitching amplitude and the frequency of the trailing-edge flap significantly affect the efficiency of the energy extraction. There is an optimal range for each of the three main parameters to maximize the energy extraction efficiency and the time average efficiency for specific angle of attack compared to the primary hydrofoil. The use of the trailing-edge flap may increase the time averaged efficiency by 81%. The flap increases the camber angle of the hydrofoil, and improves the lift coefficient of the whole hydrofoil, which leads to the improvement of the energy extraction efficiency of the hydrofoil. With the increase of lift coefficient, the drag coefficient also increases. As for the reliability and stability of the oscillating hydrofoil device, the drag of the oscillating hydrofoil should be within the range that the oscillating hydrofoil device can bear while improving the time average efficiency.