Interaction of multiple supersonic jets with a transonic flow field

The infl uence of multiple high-pressure, supersonic, radial or tangential j ets, that are inj ected f rom the c ircumference of the base plane of an axisymmetric body , on its longitudinal aerodynamic coefficients in transonic flow is studied experi mentally . The interaction of the jets with t he body f low field increases the pressures on the f o rebody. thus altering its lift and static stability c haracteristics. It is shown that, within the range of parameters studied (0.7 ~ ~ S 1.05; 20 S Poj/p~ S 70; 0° S a S 18°). this interaction has a stabilizing effect on the body. The contribution to lift and stability is significant at small angles of attack and decreases nonlinearly at higher angles when the cross flow mechanism becomes dominant. The experimental results. obtained with several injection pressure ratios. are correlated using a newly defined jet penetration height into transonic flow. An equivalent flare (or skirt ) is proposed for an approximate engineering prediction of the normal force and of the pOSition of the center of pressure. Nomenclature A throat cross-section area of injection nozzles (Eq. (12 » CD = drag coefficient. D/ qS Cj nozzle disc harge coefficient. mj /Pj VjAj CN normal f orce coefficient. N/qS Cp pressure coefficient. (p p~) /q d no zzle diameter D body diameter. also drag h jet penetration height M Mach number IiI = mass flux N normal force n number of jets p = pressure *NRC Senior Research Associate. On leave from Technion-Israel Institute of Technology. Member AIAA. ~Research Scientist. This paper is declared a work of the U.S. Government and therefore is in the public domain. 1 q = f ree-stream dynamic pressure R = gas constant S = model c ross-section area T = temperature v = velocity x = streamwise distance measured upstream from the jets a = angle of attack y = specific-heat ratio $ = circumferential angle P = density Subscripts CP = center of pressure j jet parameters o = stagnation conditions t = nozzle throat parameters = free-stream conditions Introduction Attention was first focused on the interaction of jets with external flow fields in the early fifties, with the advent of jet-propelled vehicles and the beginning of the space program. I n j et and rocket propul sion, the j et is approximately aligned with the externa l f low f ield and the interaction between them is relatively Simple . More complicated is the problem of a jet that is not aligned with the outer flow. such as retrojets or trans versal jets. This latter type of interaction can be found in short takeoff and landing (STOL) aircraft. in thrust vector control. and in direct vehicle-attitude control. It is characterized by an effective jet thrust that is larger than the conventional thrust. obtained by blowing into a stagnant medium. as a result of its interaction with the surrounding flow field. Early studies of this transonic-flow interaction phenomenon concentrated on the interaction of a Single, usually sonic. and two-dimensional jet with an external supersonic flow. Most studies were experimental because of the complexity of the problem. A few simple analytical. Semi-empirical and numerical methods were also introduced at a later stage. These methods required. however. many simplifying assumptions and were, therefore. limited to a small group of problems.