Oscillatory Blowing: A Tool to Delay Boundary-Layer Separation

TLDR

Oscillatory blowing is examined as a technique to delay boundary‑layer separation. Experiments employed a flapped NACA 01115 airfoil with a slot over the flap hinge, varying steady blowing momentum independently of oscillation amplitude and frequency. Modulated blowing increased lift, eliminated form drag, and improved performance at lower energy inputs, with optimal benefits at reduced frequencies of order unity for a flap extending 25 % of the chord and effective up to 40°.

Abstract

The effects of oscillatory blowing as a means of delaying separation are discussed. Experiments were carried out on a follow, flapped NACA 01115 airfoil equipped with a two-dimensional slot over the hinge of the flap. The flap extended over 25% of the chord and was detected at angles as high as 40 deg. The steady blowing momentum coefficients could be varied independently of the amplitudes and frequencies of the superimposed oscillations. The modulated blowing was a major factor in improving the performance of the airfoil at much lower energy inputs than was hitherto known. Optimum benefits in performance were obtained at reduced frequencies, based on the flap chord, of an order of unity. Significant increase in lift as well as cancellation of form drag were observed