Numerical study on energy-extraction performance of a flapping hydrofoil with a trailing-edge flap

Unlike traditional rotary turbines, the flapping hydrofoil energy harvesters can capture kinetic energy from flowing fluids by undergoing combined heaving and pitching motions. In this paper, a new type of flapping hydrofoil energy harvester whose trailing-edge can deflect upwards during downstroke flapping cycle and downwards during the upstroke has been proposed. The energy-extraction performance of the proposed flapping hydrofoil then was investigated by numerical simulations based on the two-dimensional incompressible NavierStokes equations at a Reynolds number of 4.7 x 10(5). Influences of various characteristic parameters including deflection angle amplitude, flap length, gap width on the energy-extraction efficiency of the proposed flapping hydrofoil were analyzed. The present results show that the heaving force is the most dominant contributor to total power output of the flapping hydrofoil and it can be greatly increased due to the deflection of TEF. It is also found that there exist optimal deflection angle amplitude and TEF length which can significantly improve the energy-extraction efficiency at moderate to high values of reduced frequency. Moreover, the smaller the gap width, the higher the efficiency can be achieved. As a result, the maximum energy-extraction efficiency of the flapping hydrofoil with optimized TEF can be increased by approximately 23.5% compared to the conventional flapping hydrofoil-based current energy harvester.