Wind-tunnel Experiment of Drag Reduction with Uniform Blowing on the Pressure Surface of an Airfoil

Abstract

We investigate the drag reduction effect of uniform blowing (UB) on the pressure surface of the airfoil by wind-tunnel experiments. The experiments are performed using a Clark-Y airfoil model. The UB is conducted by supplying air to a chamber in the airfoil model covered with porous material using an external compressor. The blowing region is installed near the leading edge of the pressure surface of the airfoil. To investigate the effect of UB on the friction drag, the velocity distribution in the boundary layer is measured using a hot-wire anemometer, and it is confirmed that the distribution shifted away from the airfoil surface by UB. Quantitative evaluation using the wall law shows that the local friction drag is reduced up to about 51% under the experimental conditions of the angle of attack α = 0° and the Reynolds number based on the chord length Re_c = 0.65 × 10⁶ and UB at 0.33% of the free-stream velocity. In addition, pressure measurements performed in the wake of the airfoil qualitatively confirm that the velocity deficit is reduced by UB on the pressure side of the airfoil, qualitatively resulting in up to 5.4% reduction in the total drag, although, the measurement uncertainty is found to be on the same order as the total drag reduction rate.