Abstract: S809 is used as the main airfoil and an auxiliary airfoil is added at its leading edge. Based on the SST k-ω model, the effect of the auxiliary airfoil on the aerodynamic characteristics of the main airfoil S809 at the angle of attack from 2°~22° are analyzed.The results show that when the leading edge auxiliary airfoil is added at the leading edge of the main airfoil, the lift force of the main airfoil is decreased and the drag force is increased at a small angle of attack of 2°~6°. However, when the angle of attack reaches 8°, the leading edge auxiliary airfoil increase the lift force of the main airfoil, the drag force is decreased and the lift-drag ratio is increased. The flow separation law and the lifting mechanism of the main airfoil at 10°, 14°, 18° and 22° are analyzed. The existence of leading edge auxiliary airfoil effectively inhibits and delays flow separation, and effectively inhibits separation bubbles at large angles of attack. As can be seen from vorticity cloud images of 10° and 18°, the vortex generated at the leading edge auxiliary small airfoil has an obvious inhibition effect on the main airfoil vortex. In the boundary layer, the x-direction velocity component at the same height is larger than that of the original airfoil, which indicates that the fluid along the x-direction of the airfoil surface has greater kinetic energy, which is helpful to improve the aerodynamic performance of the main airfoil at large angles of attack.

Key words: numerical simulation, flow separation, S809 airfoil, auxiliary small airfoil, aerodynamic performance, separation vortex