Friction drag reduction on an airfoil using passive blowing*

Friction drag reduction of a passive blowing on a Clark-Y airfoil is investigated experimentally. The passive blowing is driven by the pressure difference on the surface between suction and blowing sections. The experiment is carried out in a JAXA 0.65 m×0.55 m low turbulence wind tunnel. The Reynolds number based on the chord length is set to 0.65×10⁶ and 1.54×10⁶. The angle of attack is 0° and 6°. The streamwise mean velocity profile in the blowing section is shifted away from the wing surface, which suggests friction drag reduction by the passive blowing. We quantitatively assess the effect of blowing using log-law by taking into account the effects of pressure gradient and the roughness of the wall caused by the perforated metal plate used for blowing. In order to obtain the friction velocity, the slope of the velocity profile corrected through the modified log-law which takes into account the blowing effect is fitted to the slope of the theoretical profile with pressure gradients. As a result of this quantitative assessment, we estimate that the passive blowing reduces the local friction drag by 5% - 25%.