Energy extraction properties of a flapping wing with an arc-deformable airfoil

Abstract

The active synchronous deformation in the arc length of an airfoil employed in a flapping wing can improve its energy extraction efficiency. The present study seeks to understand the underlying physics of this energy extraction by conducting transient numerical simulations of a novel arc-deformable flapping foil design based on dynamic mesh technology and a relative heaving motion reference system. The influence of the flapping frequency and the pitching amplitude on the energy extraction efficiency of the flapping foil modeled under a constant arc length is investigated. The effects of the deformation magnitude β and the position of the deformation center on the energy extraction efficiency are also examined at a constant flapping frequency and pitching amplitude. The results show that active synchronous arc deformation can greatly improve the energy extraction efficiency of a flapping foil compared to the efficiency of a conventional non-deformable flapping foil design. In addition, the results provide sets of optimal flapping frequencies and pitching amplitudes for the deformable flapping foil design with fixed deformation parameters and the non-deformable foil design that obtains the highest energy extraction efficiencies. A single high efficiency zone is obtained for the deformable foil design at a relatively high flapping frequency. In contrast, relatively high efficiency zones are obtained for the non-deformable foil design at both a relatively low flapping frequency and a high flapping frequency. The energy extraction efficiency of the deformable flapping foil first increases with increasing β up to a maximum value of β = 0.25 and then decreases with a further increase in β. The energy extraction efficiency of the deformable flapping foil is also demonstrated to increase as the deformation center moves from the leading edge of the foil to the trailing edge, attaining a maximum value when the deformation center coincides with the center of the pitching axis, and then decreases.