An adaptive plate at flapping wing’s trailing edge in promoting energy extraction performance

Abstract

As is known, the maximum thickness position plays a key role in determining the energy extraction properties for flapping wing airfoils. Previous work demonstrated that the energy extraction efficiency might increase when we move the maximum thickness position towards the leading-edge direction. Inspired from this phenomenon, we propose in this work the addition of a flat plate at the tail of the flapping wings. Under two different Reynolds numbers (Re = 1100 and Re = 5×105), the effect of adding a rigid flat plate or a flexible flat plate to the trailing edge of the flapping wing on the flapping wing’s energy efficiency was investigated. The corresponding results were also compared with that of the original flapping wing. Results show that the addition of a rigid flat plate is sufficient for the amelioration of the flapping wing’s energy extraction efficiency in low Reynolds number cases. At high Reynolds number cases, the flapping wing with flexible flat plate trailing edge can maintain a relatively high energy extraction efficiency over a wide range of frequency, while the flapping wing with rigid flat plate trailing edge can only improve the energy extraction efficiency in the low frequency region. Therefore, we propose the application of flapping wings with flexible flat plate trailing edge for increasing the energy extraction efficiency under high Reynolds number conditions.