Experimental and computational study of infrared emission from underexpanded rocket exhaust plumes

Underexpanded rocket exhaust plumes generated in a test-bed facility are studied experimentally. Infrared (IR) images of the plume have been obtained with an IR camera equipped with narrow bandpass filters. The spectral distribution of the IR emission has been measured with a spectroradiometer. Numerical simulations of the exhaust plume have been conducted. The gas-dynamic and thermodynamic properties of the flowfield were computed by the General Aerodynamic Simulation Program computational fluid-dynamic code. On the basis of the simulated flowfield, the IR radiation was numerically calculated by using a computer program INFRAD, which has been developed for this purpose. The program calculates the radiation transfer through the plume using the statistical narrowband model technique. It allows simulation of the IR plume images as well as the local and the space-integrated plume spectra. The simulated and experimental results agree well.