Drag reduction by uniform blowing on the pressure surface of an airfoil

Drag reduction effect by uniform blowing (UB) on the pressure surface of an airfoil is investigated through wind-tunnel experiments. The experiments are conducted using a Clark-Y airfoil model. The UB is realized by supplying air from an external compressor to a chamber, covered with a porous surface, installed near the leading edge of the pressure surface of the airfoil model. To investigate the effect of UB on friction drag, velocity profiles in the boundary layer on the pressure surface are measured using a hot-wire anemometer, and it is confirmed that the velocity profiles shift away from the airfoil surface by UB. The local friction drag reduction rate is quantitatively evaluated by using the law of the wall, and about 50% local friction drag reduction is confirmed by UB at 0.33% of the freestream velocity at the chord Reynolds number Re_c 0.65 × 10⁶ . Besides, the pressure distribution in the wake is measured with a pitot tube to investigate the effect of UB on the total drag. The measurement result indicates that the total drag is reduced by UB about 5%, although the measurement uncertainty is estimated to be on the same order.