Two dimensional steady state Navier-Stokes computations were performed to determine the effect of Gurney flap on NACA 4412 and NACA 0011 airfoils. Gurney flap sizes selected for the study range from 0.5% to 4% of the airfoil chord. A compressible Navier-Stokes solver with Baldwin-Lomax turbulence model, JUMBO2D, is used to predict the flow field around the airfoils. Computed results have been compared with available experimental and computational data. There is good correlation observed between computed and experimental data. Addition of Gurney flap increases the lift coefficient significantly with very little drag penalty if proper Gurney flap height is selected. Nose down pitching moment also increases with Gurney flap height. Flow field structure near the trailing edge shows very good resemblance with Liebeckx2019;s hypothesis that provides the possible explanation for the increased aerodynamic performance