Assessment of Friction Drag Reduction on a Clark-Y Airfoil by Uniform Blowing

Effects of uniform blowing on a Clark-Y airfoil are investigated experimentally aiming at turbulent friction drag reduction. The uniform blowing is applied on the rear part of the upper surface. The experiment is carried out at the free-stream velocity of U∞=58 m/s, and the Reynolds number based on the chord length is Rec=1.5×106. The angle of attack is set to α=0° and 6°. In the velocity measurement by a hot-wire anemometry, the velocity profile in the blowing region is found to shift away from the wall. This behavior is consistent with that observed in the previous studies on a flat plate, and it qualitatively suggests that the local friction drag is reduced by uniform blowing. Subsequently, this study attempts a quantitative assessment of the local friction drag reduction rates by fitting the mean velocity profile to the log-law taking into account the pressure gradient and the blowing effect. From this, this study has confirmed about 20–40% local friction drag reduction due to blowing. Unfortunately, however, the total drag estimated from the wake pressure profile is found to increase slightly by blowing.