Investigation on Infrared Radiation Signatures of Under-Expanded Rocket Exhaust Plumes Due to Angle of Attack

A real flight trajectory varying from 5–60 km altitude was adopted for analyzing the effects of the angle of attack (AOA) on the IR signatures of rocket exhaust plumes. Three representative under-expanded states based on nozzle pressure ratio (NPR), including moderately under-expanded (NPR = 1.27), highly under-expanded (NPR = 12.5), and over-highly under-expanded (NPR = 120) states, were discussed. The results show that the appearance of the AOA shortens the plume scale size and afterburning region, but the peak temperature cannot significantly change. As an increase in the AOA, the high-temperature region and Mach cells are compressed to a small domain. The spectral radiant intensity is reduced and the decreasing rate is gradual for a large AOA. The peak radiance in the $2.7~\mu \text{m}$ band decreases, but that in the $4.3~\mu \text{m}$ band increases. The peak radiance curve shifted toward the increasing NPR as the AOA increases, and then the curve decreases monotonically from an initial “arched” shape. In addition, a group of band pairs can be observed by two intersecting in-band profiles as a function of altitude. The characteristic altitude of band pairs became more concentrated and moved toward low altitude with the increase in AOA.