  Effects of a gurney flap were numerically investigated on the supercritical
NASA airfoil by solving the two-dimensional Reynolds-averaged Navier-Stokes
equations for a range of transonic Mach numbers and angles of attack, using
turbulence compressible KW SST model. The height of the gurney flap was
selected to be 1.65 percent chord length. A high-resolution mesh was applied to
accurately predict the flow field specifically in the vicinity of the airfoil.
Below the drag divergence Mach number, the gurney flap has a remarkable
influence on the aerodynamic coefficients especially at -1 and 0 degrees angle
of attack resulting in 50 percent increase in L over D ratio. At high Mach
numbers and angles of attack, Gurney flap loses its effects and the clean
airfoil has better aerodynamic performance since it significantly boosts both
the pressure and shear drag. It was observed that the gurney flap mitigates the
transonic lambda shock on both surfaces of the airfoil. Moreover, it alters the
Kutta condition by changing the separation point location at the trailing edge
which provides the airfoil more bound circulation and lift force.
