Experimental investigation on friction drag reduction on an airfoil by passive blowing

Abstract

Friction drag reduction effect of a passive blowing on a Clark-Y airfoil is investigated. Uniform blowing, conducted in a wall-normal direction on a relatively wide surface, is generally known as an active control method for reduction of turbulent skin friction drag. In the present study, uniform blowing is passively driven by the pressure difference on a wing surface between suction and blowing regions. The suction and the blowing regions are respectively set around the leading edge and the rear part of the upper surface of the Clark-Y airfoil in order to ensure a sufficient pressure difference for passive blowing. The Reynolds number based on the chord length is 0.65×10 6 and 1.55×10 6. The angle of attack is set to 0 • and 6 •. The mean streamwise velocity profiles on the blowing region and the downstream, measured by a traversed hot-wire anemometry, are observed to shift away from the wall by passive blowing. This behavior qualitatively suggests reduction of local skin friction on the wing surface. A quantitative assessment of the friction drag is performed using the law of the wall accounting for pressure gradients (Nickels, 2004), coupled with a modified Stevenson's law (Vigdorovich, 2016) to account for the weak blowing. From this assessment, the local friction drag reduction effect of passive blowing is estimated to reach 4% − 23%.

Parametric study toward optimization of blowing and suction locations for improving lift-to-drag ratio on a Clark-Y airfoil

“…As for the controlled cases, not only the single control of either UB or US but also the combined control of UB and US at the equal flow rate are considered assuming a practical situation where the air required for UB is taken from the other region of the airfoil, as has been attempted in the recent experiment by Hirokawa et al (2020). In the single UB/US cases, we apply the blowing or suction velocity of 0.14%U ∞ , denoted as B014 and S014, respectively.…”