Narrow-band infrared radiation characteristics of rocket exhaust plume by using correction function related to thermodynamic state

Abstract

Modeling of plume infrared radiation requires the accurate calculation of gas radiation properties of the plume non-uniform flow field. Aiming at the problem that the Curtis-Godson approximation (CGA) method can give the exact result in the limits of weak lines and strong lines, but overestimates the absorption of the optical intermediates path. This study develops an accurate model to study the infrared radiation of rocket plume. This model calculates narrow-band radiation properties using an equivalent half-width corrected by a correction function, which relates to the thermodynamic state of the no-uniform plume and is followed by radiative transfer calculations. Several Lorentz single lines were adopted to evaluate this correction function by the equivalent width of a fictitious non-uniform gas column, results showed high accuracy, especially at optical intermediates. Simulation of plume reaction flow was implemented by a refined 11-species, 17-reaction chemistry scheme, which can describe the afterburning between the multi-component fuel injected from the nozzle and ambient air. Then, adopting the temperature, pressure and radiating species distribution of the plume flow field, the model can predict accurate spectra that fit the experimental spectrometer data well. Finally, the effects of propellant formulation and flight conditions on plume infrared radiation were investigated: (a) hydroxyl-terminated polybutadiene (HTPB) and nitrate ester plasticized polyether (NEPE); (b) flight altitude; (c) flight Mach number. Results show that the composition of the propellant has a significant effect on the plume afterburning, NEPE plume afterburning effect is stronger, and the total radiation intensity is 61.5% higher than HTPB in 1.5–6.0 μm. The increase of flight altitude weakens the radiation, while due to the expansion of the radiant area, the spectral radiation intensity increases significantly. With the increase of Mach number, the band intensity decreases exponentially, and the plume structure gradually develops into a slender shape, the radiation decreases significantly. The research has significance for the application of target early warning, detection and identification.