Abstract
A two-dimensional numerical investigation was conducted to determine the effect of a modified Gurney flap configuration on S823 and S822 aerofoils (from the NREL aerofoil family). The device used consists of a flap in the order of 1-3% of the aerofoil chord in length, oriented perpendicular to the chord line and located on the pressure side at 96% of the chord from the leading edge. The remaining 4% of the chord was eliminated similarly to the structure of blunt trailing edge aerofoils, for the purposes of drag reduction and structural stability. The flow field around the aerofoil was numerically predicted using an incompressible Navier-Stokes solver and the two-equation turbulence model k-epsilon at different Reynolds numbers. The numerical results show that the flaps increase the aerofoil lift coefficient and slightly decrease the drag coefficient. The data obtained show that flaps with high length increase drag significantly. It was found that using a flap length of 2% of the chord at angles of attack ranging from 4(0) to 6(0) increases lift to drag ratio to reach its maximum value (increases by 97%)