Microblowing for High-Angle-of-Attack Vortex Flow Control on a Fighter Aircraft

Abstract

Effectiveness of the microblowing technique for controlling forebody vortex asymmetry at high angles of attack has been investigated in low-speed wind-tunnel experiments with the F-15E ghter aircraft con guration. One blowing-port installation, based on previous experiments with generic forebody shapes, was evaluated. At very high angles of attack (® >50 deg), microblowing was effective in generating and controlling yawing moment levels comparable to those demonstrated by high-pressure jet nozzle blowing, while requiring only 1 100 as much mass ow, demonstrating the leveraging available through controlling the vortex ow eld at the point of instability. The microblowing port con guration employed was unable to generate usable yawing moments at moderate angles of attack (® < -35 deg). Control-port optimization promises to improve microblowing effectiveness in the intermediate ® range. Nomenclature A= reference area for all coef cients: forebody planform area for isolated forebody; wing planform area for F-15 C P m = control-jet mass-ow-rate coef cient, C P m D P m j =½ 1 U 1 A C N = normal force coef cient C n = yawing-moment coef cient C Y = side-force coef cient D = base diameter of F-15E model forebody d = diameter of control-jet ori ce F Y = side force P m j = mass-ow rate of control jet Re = Reynolds number based on D, U 1 D=º 1 T = equivalent sonic-jet thrust U 1 = freestream ow speed x = axial distance from (virtual) apex of tangent ogive forebody ® = angle of attack = sideslip angle º 1 = kinematic viscosity of freestream air ½ 1 = freestream air density Á = azimuthal angle (from windward meridian) Ã = yaw angle

Modification of the wake behind a circular cylinder by using synthetic jets

“…For example, a pulsed jet has been implanted on a two-element flat plate model by McManus et al (1995): the wind tunnel experimental results illustrate the efficiency of the actuators in inhibiting separation and delaying stall. Roos et al (1993Roos et al ( , 1996Roos et al ( , 1997 have tested microblowing on a fighter aircraft. Very small flush ports, implanted at the nose of a blunted hemisphere-cylinder forebody, delivered a pulsed jet which controlled the flow and could produce a steady change in flow asymmetry.…”

Forebody Flow Control at Conditions of Naturally Occurring Separation Asymmetry

“…0:00020) before the effect of the initial geometric microasymmetry, dominant at C P m D 0, could be overpowered, causing the constant-magnitude side force to change direction. (Note the unusual de nition of positive side force, 9 used here as well as in Figs. 6 and 7 to be discussed later shown in Figs.…”

“…3;4 Because of the nature of the separation asymmetry at ® > 2µ A , it is relatively easy to control the direction of the generated side force at high angles of attack but very dif cult to control its magnitude, as has been demonstrated by the effect of microblowing. 9 Starboard-side forward blowing at » D 0:20 and Á D 135 deg on the nose of a smooth, pointed 3.5-caliber tangent-ogive was used to promote cross ow separation, giving the results shown in Fig. 3.…”

Mechanism of perturbation-combined active control technique for asymmetric vortex flow over slender body at high angle of attack

“…In some techniques, the microblowing or unsteady bleeding as a nose disturbance is used to manipulate the forebody asymmetric vortices. In the experimental studies by Roos [3,14,15], Williams [6][7][8] and Malcolm [1,2] et al, the control ports consisted of two small holes on each side of nose tip and were located at ±135° from the windward meridian of the forebody. However their experimental results have shown that if angle of attack is high enough, such as =50, the asymmetric vortices over slender body present the behavior of bistable state, and the available results show that the behavior of asymmetric vortices is too sensitive to blowing perturbation.…”