Onset of aerodynamic side forces at zero sideslip on symmetric forebodies at high angles of attack

Keener, Earl R.; Chapman, G. T.

doi:10.2514/6.1974-770

Cited by 75 publications

(19 citation statements)

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“…The baseline (C P m D 0) case shows nonzero C n for ®¸48 deg, a peculiarity of the nose shape on this particular F-15E model that was identi ed previously. 10 Interestingly,the onset ® for the appearance of vortex asymmetry (as evidenced by C n 6 D 0) is consistent with Keener and Chapman's rule-of-thumb that the onset ® is approximately twice the half-angle at the forebody apex 11 if account is taken of the F-15 forebody droop angle of »5 deg. It is evident in Fig.…”

Section: Resultssupporting

confidence: 70%

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

Roos

2001

Journal of Aircraft

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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

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Section: Resultssupporting

confidence: 70%

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

Roos

2001

Journal of Aircraft

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“…A notable one is the generation of a large side force on the forebody, even when the ight vehicle is at zero side slip. The side force, which can be as large as 1.5 times the normal force, 1,2 has been attributed by many to the asymmetric shedding of the forebody vortices. An added complication to this phenomenon is that the traditional control surfaces operating under this condition are ineffective in overcoming the yawing moment created by the side force because they are likely to be immersed in the wakes of the wings and the forebody.…”

Section: Pmentioning

confidence: 99%

“…= pressure coef cient, (P ¡ P 1 )/ (0.5q U 2 1 ) C y = side force coef cient, F y / (0.5q U 2 1 S) C y( X) = local side force coef cient, local side force/ (0.5q U 2 1 D sin 2 a ) D = cylinder diameter F y = side force L = length of body P = pressure on model surface P 1 = freestream static pressure M ODERN aircraft and missile are required to operate agilely at high angles of attack. However, operating under this condition can lead to several adverse effects.…”

Section: Pmentioning

confidence: 99%

Helical-Groove and Circular-Trip Effects on Side Force

Lua

Lim

Luo

et al. 2000

Journal of Aircraft

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When a slender body, such as a missile, is pitched at high angle of attack to an oncoming ow, it may experience a large side force due to the asymmetric shedding of the tip vortices. The side force is well known to be highly detrimental to the performance of the ight vehicle. We assess the effectiveness of two control devices, namely, the circular trips and the helical grooves, in alleviating the side force on a tangent ogive nose cylinder. Simultaneous side force and pressure measurements taken in a wind tunnel show that the circular trip is generally more effective in reducing the side force than the helical grooves over a wide range of angle of attack. Detailed ndings of their performances are reported. Nomenclature C p= pressure coef cient, (P ¡ P 1 )/ (0.5q U 2 1 ) C y = side force coef cient, F y / (0.5q U 2 1 S) C y( X) = local side force coef cient, local side force/ (0.5q U 2 1 D sin 2 a ) D = cylinder diameter F y = side force L = length of body P = pressure on model surface P 1 = freestream static pressure Re D = Reynolds number, U 1 D/ m S = model base area, p D 2 / 4 U 1 = freestream velocity X = axial distance from nose tip a = angle of attack d N = tip semi-apex angle h = azimuth angle around circular cross section measured from the most leeward position m = kinematics viscosity of uid q = density of uid u = roll angle

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“…27 Thus, experimental results indicate that the flow process leading to vortex asymmetry is radically different in the case of a pointed, slender nose from what it is on the cylindrical aft body, the case which until now has received almost all attention, at least in theoretical investigations. It has been noted by Keener and Chapman 54 that the a. boundaries for incipient asymmetric loads at zero sideslip are very similar for slender bodies 10 and delta wings 55 when plotted against the fineness ratio. They suggest, therefore, that the vortex asymmetry in both cases is caused by a basic hydrodynamic instability resulting from the "crowding together" of the vortices.…”

Section: Nose-induced Asymmetric Vorticesmentioning

confidence: 90%

Steady and Unsteady Vortex-Induced Asymmetric Loads on Slender Vehicles

Ericsson¹,

Reding²

1981

Journal of Spacecraft and Rockets

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b c C m D d ' d d J I 1 L M M n N P N q Re R d S S t U x Y a a /3 7 Nomenclature wing span reference length , c = d f or bodies dC m /da;Ce f3 = dC e /d0 drag,coefficentC z> =Z)/(p 00 t/i/2)S sectional drag , coefficient c d = d ' I ( p «, U 2 , /2)c maximum diameter for body of revolution mean diameter, d=\ J 0 2 rd(x/£) bio wing momentum, coefficient body length forebody length forward of rotation center (Fig. 8) nose length = rolling moment, coefficient C, = £/ (p* U^ /2)Sb vortex wake wave length Mach number pitching moment, coefficient C m =M p /( Poo Ul/2)Sc yawing moment, coefficient C n =n/(p 00 U 2 00 /2)Sc = normal force, coefficient C N =N/ (p^ C/i/2)S = nose tip roll rate = pitch rate Reynolds number based on d max and freestream conditions; usually Re = R d Reynolds number, R d = U^d/vr eference area, S = ird 2 /4 reference area ( = projected wing area) time velocity axial body-fixed coordinate (distance from apex) side force, coefficient C Yangle rotation of plane of symmetry of forebody vortices (Fig. 8) cone half-angle 6 A = apex half-angle p = air density = roll angle <£' = coning angle (Fig. 8) 5 = three-dimensional separation angle (Fig. 15) a' = total angle of inclination (Fig. 8) v -kinematic viscosity oj = angular rate Subscripts A = apex AM = effective apex angle A V = asymmetric vortices c = cone n = normal to body axis TV =nose P = port side s = separated flow S = starboard SV = symmetric vortices UV = unsteady vortices v = vortex W =wall oo = freestream conditions Introduction T HE continually increasing performance demands on present day aircraft and missiles have brought on intensive research aimed at providing the needed understanding of the vehicle aerodynamics at high angles of attack where separated flow vortices often have a dominating influence. Recently there has been a series of papers reviewing the state of the art for the prediction of these high-a aerodynamics. M Nielsen 1 ' 2 concentrated his attention on the existing capability of predicting the missile aerodynamics at high angles of attack where the effects of symmetric vortices Lars E. Ericsson has published more than 100 papers in his related fields. Pete Reding, an Associate Fellow of AIAA, has had roughly 22 years experience in the aerospace industry working generally in the field of unsteady aerodynamics. He was first mystified by body vortex effects during his two-and-a-half years at what was then Douglas Aircraft Company, where he worked immediately after graduation from the University of Michigan in 1958. Now at Lockheed Missiles and Space Co., Inc. (since 1961) he has wrestled with separated flows, booster aeroelastic stability, airfoil stall, the dynamics of bulbous based bodies, ablating bodies, shuttle vehicles, decelerators, dynamic support interference, and aeroacoustics. Not one to give up easily he has once again attacked the mysteries of body vortices. 98 L.E. ERICSSON AND J.P. REDING J. SPACECRAFTfrom the forebody and its canard surfaces on aft body and fins have demanded major new analytical/ex...

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Onset of aerodynamic side forces at zero sideslip on symmetric forebodies at high angles of attack

Cited by 75 publications

References 0 publications

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

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

Helical-Groove and Circular-Trip Effects on Side Force

Steady and Unsteady Vortex-Induced Asymmetric Loads on Slender Vehicles

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