A two-dimensional numerical investigation was performed to determine the effect of a Gurney flap on a NACA 4412 airfoil. A Gurney flap is a flat plate on the order of 1-3% of the airfoil chord in length, oriented perpendicular to the chord line and located on the airfoil windward side at the trailing edge. The flowfield around the airfoil was numerically predicted using INS2D, an incompressible Navier-Stokes solver, and the one-equation turbulence model of Baldwin and Barth. Gurney flap sizes of 0.5%, 1.0%, 1.25%, 1.5%, 2.0%, and 3.0% of the airfoil chord were studied. Computational results were compared with available experimental results. The numerical solutions show that some Gurney flaps increase the airfoil lift coefficient with only a slight increase in drag coefficient. Use of a 1.5% chord length Gurney flap increases the airfoil lift coefficient by ΔC_l ≈ 0.3 and decreases the angle of attack required to obtain a given lift coefficient by Δα_(L = 0) > - 3°. The numerical solutions show the details of the flow structure at the trailing edge and provide a possible explanation for the increased aerodynamic performance.
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