Underexpanded jet-freestream interactions on an axisymmetric afterbody configuration

Abstract

Experimental investigations are carried out in the 0.3 m trisonic wind tunnel at NAL to study exhaust jetfreestream interactions on an axisymmetric afterbody configuration. The model chosen for these studies is an equivalent body of revolution of a representative combat aircraft configuration. The effects of jet pressure ratio and freestream Mach number on boattail, base, and afterbody pressure drag are studied along with color Schlieren flow visualization of the afterbody flowfield. Experiments are carried out in the freestream Mach number range of 0.6 to 1.1 at Reynolds number from 20 × 10⁶/m to 35 × 10⁶/m keeping model at zero degree of incidence. Jet pressure ratio is varied from 1 to 6 during this investigation. The jet at nozzle exit is sonic throughout these tests. Experimental results show that the underexpanded jet plume affects predominantly the afterbody pressure distribution and hence the afterbody pressure drag. Upstream influence of the jet extends even up to the boattail shoulder and is predominant in the region of freestream shock location over the afterbody at transonic speeds. The movement of shock location determined from color Schlieren flow visualization studies agree well with the theoretical predictions made on the basis of transonic small perturbation calculations.