Parametric research and aerodynamic performance analysis of wind turbine airfoil with added flap

A self-popped up flap is added to the airfoil (S809) suction surface to improve aerodynamic performance under large angle of attack (AOA) inspired by the slightly popped up feathers on the trailing edge of a bird’s wing. The response surface methodology (RSM) optimization of H, D, and θ is conducted. The lift–drag ratio of an airfoil is taken as the optimization response target, and the Box–Behnken design is adopted to design the experiment scheme for H, D, and θ. Multivariate quadratic polynomials are used to carry out equation regression analysis on the combined results of 17 sample schemes, and the mathematical surrogate model between the flap structure parameters and the airfoil lift–drag ratio and the optimal design parameter combination of the flap structure are obtained. The clean airfoil and the airfoil with optimal flap are compared and analyzed from the static and dynamic aerodynamic characteristics by numerical simulation. The calculation results show that the optimal flap obtained by RSM increases the pressure difference between the suction and the pressure surfaces at large AOA, suppresses flow separation on the suction surface, and delays the stall AOA. The airfoil with optimal flap leads to a smaller separation vortex and wake vortex, therefore delaying the dynamic stall effect.