Turbulent separation control on an airfoil surface using a wavy wall

This study investigates the effects of two-dimensional streamwise wall waviness (WW) on turbulent boundary layer separation over an airfoil surface (National Advisory Committee for Aeronautics, NACA 4412) under adverse pressure gradient (APG) conditions. Various WW configurations are analyzed at a friction Reynolds number Reτ=2500 to identify the most effective design for delaying flow separation. The most beneficial configuration (W4) is further examined under Reτ=1200−2500 to assess the sensitivity of its performance to changes in Reτ. Results show that the effective slope (ES) parameter significantly influences separation delay and wall shear stress (τw) enhancement. Separation is maximally delayed at ES≈0.17, beyond which the trend reverses. A strong correlation between the wavelength (λ) of WW and the downstream shift of the separation point is observed with increased λ leading to higher τw, while amplitude (A) shows no clear correlation. The enhancement of τw is highly dependent on the Reynolds number; the beneficial effects of W4 are prominent at Reτ=2500 but diminish at lower values. It is demonstrated that the effectiveness of WW remains consistent whether it is integrated into a flat wall subjected to an external APG source or into a curved surface of an airfoil.