Computational Study of Unsteady Flows around Dragonfly and Smooth Airfoils at Low Reynolds Numbers

A computational study was conducted to investigate the unsteady quasi-two-dimensional flow around a streamlined NASA low-speed GA(W)-1 airfoil and a corrugated dragonfly airfoil at the Reynolds numbers of 68,000 and 55,000. Both 2D and 3D simulations were carried out by solving the unsteady Navier-Stokes equations to predict the behavior of the unsteady flow structures around the airfoils at different angles of attack (AOAs). Extensive comparisons were made between the numerical results and wind-tunnel experimental results for the same configurations. It was found that the 2D and 3D simulations differ significantly at relatively high AOAs, and that the 3D computational results agree much better with the experimental data. It is believed that unsteady vortex-dominated flow at high angle of attack is strongly three-dimensional. As a result, the 2D simulations are not adequate in resolving the fundamental flow physics, and 3D simulations are necessary to correctly predict the flow behavior at such conditions.