Unsteady Flow Features of a Flapping and Pitching Wing at Low Reynolds Number

Abstract

The unsteady flow field of a flapping-and-pitching flat plate wing of elliptic planform at a nominal Reynolds number, Re c = 4100 and reduced frequency, k = 0.138, was studied using flow visualization. Hydrogen bubbles and dye were employed as tracers. The study reveals many vortical flow features. The trailing edge vortex shows very interesting dynamics immediately following pitching at stroke reversal. A leeward surface spanwise flow towards the wing tip immediately following stroke reversal is observed. A vortex trapping model is proposed to explain enhanced lift observed in insects. The study has applications in flow control and micro air vehicle design and development.