NUMERICAL INVESTIGATION OF TURBULENT FLOW AROUND A STEPPED AIRFOIL AT HIGH REYNOLDS NUMBER

This study presents the numerical simulation of flow development around NACA-2412 airfoil which utilized the backward facing step to explore the possibility of enhancing airfoil aerodynamic performance by trapped vortex lift augmentation. This article concentrate on the effect of separated flow and following vortex formation which is created by backward facing step on pressure distribution and subsequently on lift and drag coefficient. Reynolds number that based on the free stream velocity and airfoil chord is 5.7x10(6). The two-equation shear stress transport (SST) k-omega turbulence model of Menter is employed to determine accurately turbulent flow, as well as the recirculation pattern along the airfoil. The Reynolds-averaged Navier Stokes (RANS) equations are solved numerically using finite volume based solution with second-order upwind Roe's scheme. Steps are located on both suction side and pressure side of the airfoil, at different locations, different lengths and various depths in order to determine their effects on lift, lift to drag ratio and near stall behavior. The modeling results showed that all stepped airfoil cases studied experienced higher drag compared to the base airfoil. Considerable lift enhancement was found for airfoil with backward facing step on pressure side at all values of angle of attack because of trapped vortex. The results suggest that the steps on the lower surface that extended back to trailing edge can lead to more enhancement of lift to drag ratio for some angles of attack; while the rear locations for the step on upper surface was found to have negative effect on lift to drag ratio. Based on this study, the backward facing step on suction surface offers no discernable advantages over the conventional airfoil but showed some positive effect on delaying stall.