On the optimal morphology and performance of a modeled dragonfly airfoil in gliding mode

Abstract

Numerical investigation on the effect of wing morphology of the dragonfly Aeshna cyanea is carried out to understand its influence on the aerodynamic performance. The two-dimensional wing section has corrugation all over the surface along the chord length on both upper (suction side) and lower (pressure side) surfaces. By considering each corrugation separately on different airfoils at their different positions, 10 single corrugated airfoils were generated. Simulations are performed on these different airfoils to determine the effect of each corrugation on aerodynamic performance. The flow is modeled as incompressible, Newtonian, homogeneous, and unsteady. The angle of attack was varied from 0° to 20°, and the Reynolds number (Re) was varied from 150 to 10 000. The optimum morphology and angle of attack were predicted by using the surrogate-based optimization technique for a maximum gliding ratio at different Re. A fully corrugated pressure side gives the best performance at angles of attack of 9.79° and 14.83° at low Re. At high Re, corrugations on the pressure side which are in the middle and those near the trailing edge give a maximum gliding ratio at angles of attack 9.22° and 5.276°. The spatiotemporal dynamics indicate that corrugations near the leading edge on the upper surface and corrugations near the trailing edge for the lower surface and which are in the middle are beneficial. It is also found that shear drag due to corrugation decreases but pressure drag increases; therefore, the overall drag coefficient for a fully corrugated airfoil increases. Corrugations on the suction side have little influence, while those on the pressure side causes lift enhancement.