Development of underexpanded sonic jet exhausting from the convergent nozzle of an axisymmetric afterbody configuration

Experimental investigations were carried out to study the development of underexpanded sonic jets and the effect of jet plume boundary shape on the pressure drag characteristics of an axisymmetric afterbody configuration. Experiments were conducted in the free stream Mach number range of 0.6 to 1.20 with the Reynolds number varying from 7.5 x 10 to the 6th to 13 x 10 to the 6th (based on the length of the model) keeping the model at zero degree of incidence. The jet pressure ratio was varied from 1 to about 6. The jet at the nozzle exit was 13; sonic throughout these tests. Experimental results show that the jet plume displacement effect on the afterbody flow is predominant at transonic free stream Mach numbers while the jet plume entrainment effect is predominant at subsonic/high subsonic free stream Mach numbers. The resultant effect of the increase in initial inclination13; of jet plume (with the increase in jet pressure ratio) caused favorable jet- free stream interactions causing the decrease in afterbody pressure drag. Jet plume-induced base pressure for the axisymmetric air nozzle correlated with the jet induced effects of other axisymmetric nozzles by matching the thrust coefficient based on the nozzle lip condition