Experimental study of a passive control of airfoil lift using bioinspired feather flap

This paper presents a systematic experimental investigation on a passive flow control of a NACA0012 airfoil using real feather flap which is installed on the pressure surface. The focus of the present study is to determine the major role of a real feather flap in the aerodynamic performance of a NACA0012 airfoil at small attack angles (α). The feather flap width w and its installation position xin are varied from 0.27c to 0.8c and from 0.0 to 0.2c, respectively, where xin is measured from the leading edge of the airfoil, and c is the chord length of the airfoil. Detailed Particle Image Velocimetry (PIV) measurements are conducted to understand the origin of the aerodynamic benefits introduced by the feather flap. When mounted on the pressure side, the feather flap is proved to be beneficial to improve the aerodynamic performance of the airfoil at small α (= −4° to 8°). The lift CL and lift-to-drag ratio CL/CD are enhanced by 186% and 72%, respectively, for w = 0.53c, xin = 0.2c at α = 2°. Time-averaged vorticity and streamwise velocity around the flapped airfoil weaken and decrease, respectively, compared with those around the plain airfoil, which are attributed to the increased CL and CL/CD.