Effects of periodic spanwise blowing on delta-wing configuration characteristics

Abstract

Periodic leading-edge spanwise blowing was tested on a 60-deg swept delta-wing fighter aircraft model in a low-speed wind tunnel, up to an angle-of attack of a = 60 deg. At low frequencies, lift and drag coefficients correspond to the pulsating blowing pressure: when the valve is open, they reach the same values as with continuous blowing, and when it is closed, they agree with the no-blowing values. A lag in the response time is observed, which is equal at low incidences to the freestream convective time, but increases to 30 convective times at a = 30-40 deg. This response time is much longer when the valve closes than when the valve opens at a = 20-30 deg. These features are similar to those of delta wings in unsteady flows, such as in pitching or plunging motions. They are insensitive to the flow parameters and are valid at low blowing frequencies. At high frequencies, lift and drag coefficients do not correspond to the pulsating pressure, but remain at an intermediate value between those of continuous and no blowing. In both cases, the mean lift and drag coefficients are equal to the values obtained by continuous blowing at the same mean momentum coefficient. Nomenclaturenozzle internal diameter / = blowing frequency k = reduced blowing frequency, 2nf • c/V m -jet mass flux P = static pressure downstream of the valve q = freestream dynamic pressure r = relative pulse length (pulse/period ratio) R c = chord Reynolds number, V • c/v S = wing planform area T = pulsating period t = time t r = response time of the aerodynamic coefficients r* = dimensionless response time, t r /t Q t$ = convective time of the freestream on the wing, c/ V V = freestream velocity Vj = jet exit velocity a = angle of attack v = kinematic viscosity

Separation drag reduction through a spanwise oscillating pressure gradient

“…Some authors applied blowing over the separation line of supersonic airfoils (Bradley & Wray 1974; Meyer & Seginer 1994; Wong & Kontis 2007) or backward-facing steps (Chun, Lee & Sung 1999), effectively reducing the reattachment length. More recent studies, such as Brackston, Wynn & Morrison (2016 b ), have employed extremum-seeking feedback control, implemented via pulsed-jet actuators, to minimize the separation drag given by a bluff-body wake.…”