Numerical Investigation into Single and Double Gurney Flaps for Improving Airfoil Performance

The impact of single and double Gurney flaps of heights within the range of [Formula: see text] is determined for a typical symmetrical airfoil (NACA 0015) by numerical simulations using an unsteady Reynolds-averaged Navier–Stokes approach. The optimal scaling of the Gurney flap to maximize the lift-to-drag ratio of the airfoil is revisited and confirmed to depend on the boundary-layer thickness in the region where it is deployed. Appropriate scaling rules for both single and double Gurney flap are proposed. Studying the Gurney flap’s pressure distribution at a finely resolved level highlights its effect on the overall foil’s pressure distribution. Finally, the unsteady simulations carried out are harnessed to determine the shedding frequencies generated by the flaps and the flow structures associated with them, hinting at the physical mechanisms by which Gurney flaps may increase lift at a low drag cost, thus improving the lift-to-drag ratio of the airfoil.