Delay of airfoil stall by periodic excitation

TLDR

Airfoil flow over slotted flaps depends on slot geometry, Reynolds number, and flap deflection, but incremental performance gains are largely insensitive to Reynolds number when it is large. Oscillatory blowing delays airfoil separation more effectively than steady blowing, but the effect depends on slot location, jet momentum, oscillation frequency, airfoil shape, and incidence, and the oscillations produce little lift variation or pressure‑center meandering. C* C D = dp Ct = T.

Abstract

It was recently demonstrated that oscillatory blowing can delay separation from a symmetrical airfoil much more effectively than the steady blowing used traditionally for this purpose. Experiments carried out on different airfoils revealed that this flow depends on many parameters such as, the location of the blowing slot, the steady and oscillatory momentum coefficients of the jet, the frequency of imposed oscillations, and the shape and incidence of the particular airfoil. In airfoils equipped with slotted flaps, the flow is also dependent on the geometry of the slot and on the Reynolds number in addition to the flap deflection that is considered as a part of the airfoil shape. The incremental improvements in single element airfoil characteristics are generally insensitive to a change in Reynolds number, provided the latter is sufficiently large. The imposed oscillations do not generate large oscillatory lift nor do they cause a periodic meander of the c.p. C* C D = dp Ct =