Parametric analysis of an oscillating wing energy harvester with a trailing edge flap

This study investigated the optimal energy harvesting conditions of an oscillating wing with a trailing edge flap for various parameters such as flap length and maximum wing and flap pitch angles. Numerical simulations were performed for flap lengths ranging from 20 % to 70 % of the chord length (c). The maximum wing pitch angle varied from 40° to 75°, whereas the maximum flap pitch angle varied from 15° to 60°. Results show that the power output performance of a large flap is higher than that of a short flap. This is because the incoming fluid is deflected relatively more vertically by a large flap than by a short flap at the same maximum wing and flap pitch angles. Consequently, the momentum change is enhanced in the direction of the heaving motion, which eventually improves the power output performance. In addition, the camber of the wing increases with flap length, leading to an increase in incoming fluid velocity on the leeward surface of the wing. This caused a decrease in leeward surface pressure for large flaps, resulting in an increased pressure difference on the wing surfaces, which assisted in enhancing the heaving force and power. The maximum power output was obtained at a maximum wing pitch angle of 70° for a flap length 20 % of c, and it was reduced to 45° for a flap length 70 % of c. However, the optimum maximum flap pitch angle varied between 35° and 45° for varying flap lengths. The power output and efficiency were improved by around 27 % and 21 %, respectively, compared with an oscillating wing without a flap, and this was achieved for a flap length 60 % of c with the maximum wing and flap pitch angles of 50° and 45°, respectively.