Aerodynamic Characteristics of a Dragonfly Wing Section in Gliding Flight

摘要

The aerodynamic characteristics of a corrugated cross section based on the forewing of a dragonfly (Aeshna cyanea) during gliding flight was studied by using the method of large eddy simulation at Reynolds number 10,000.In addition to the corrugated airfoil, simulations have also been carried out for its profiled airfoil and flat plate. The simulations demonstrated that a corrugated airfoil could produce more lift than a profiled airfoil with the same cross-section or a flat plate, with a moderate drag closely. The rotating vortices fully filled in the valleys of the corrugated airfoil along the chordwise, changing the effective aerodynamic profile similar to a ‘streamlined' airfoil. Multiple stagnation points firstly observed on the lower surface result in the pressure on the lower surface which contributes much more than the suction on the upper surface for lift generation, a much higher lift value than its profiled airfoil or flat plate is the result of combining of the rotating vortices with multiple stagnation points. The fundamental reason for a low drag is that the component of drag i.e. the skin friction drag contributes little even negative value because of the recirculation zones which formed within the corrugations. Furthermore, the results also indicated that the corrugated airfoil has much better performance over its profiled airfoil and flat plate in suppressing the large scale flow separation and delaying the airfoil stall.