Friction drag reduction on a clark-Y airfoil using 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 both actively using a compressor and passively using the pressure difference on the airfoil. The experiment is carried out at the free-stream velocity of 58 m/s: the Reynolds number based on the chord length is 1.5 × 10⁶. The angle of attack is set to 0^◦ and 6^◦ in the active blowing case and 6^◦ in the passive blowing case. In the active blowing case, the velocity profile in the control region is shifted 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. We have also attempted a quantitative assessment of the control effect; however, it is found to be difficult because we need an exact value of velocity gradient on the wall and also need to consider how pressure gradient affects on the flow behaviors in control regions, which cannot be measured directly. Therefore, the velocity profile in the boundary layer is corrected through modified log-law by taking into account the blowing effects and fitted to the theoretical profile with pressure gradients to determine the friction velocity. Through these procedures, we estimate 40% local friction drag reduction at most. In addition, we confirm that passive blowing control is feasible, and the local friction drag is reduced by it.