Speaker
Description
High-temperature exhaust plumes may represent a significant source of infrared radiation in propulsion-related high-speed flows. Their emission depends on the local thermochemical state of the gas, the spatial distribution of radiating species, self-absorption along the optical path, and the viewing direction. A consistent coupling between CFD flow-field solutions and spectrally resolved radiative transfer is therefore required to predict observable infrared quantities and to assess the interaction between radiation and the plume flow field.
In this work, a CFD-to-radiation framework is presented for predicting infrared emission from high-temperature exhaust plumes. The methodology adopts a one-way coupling strategy, in which temperature, pressure, species concentrations, and geometrical information extracted from the CFD solution are used to reconstruct the radiating and absorbing gas domain. Spectral absorption coefficients are evaluated through a detailed line-by-line treatment based on molecular spectroscopic databases, accounting for transition line positions, temperature-dependent line intensities, pressure-broadening effects, and the local thermochemical state of the plume.
Radiative transfer is then solved for multiple prescribed observation directions through a line-of-sight marching procedure. Along each ray, the emission–absorption equation is integrated using a segment-wise analytical solution, where the local source function is given by the Planck spectral radiance at the gas temperature. This formulation naturally accounts for both local gas emission and attenuation by the intervening plume medium. The resulting spectral radiance is integrated over selected infrared bands and projected onto an equivalent observation plane, providing synthetic radiometric maps and band-integrated plume intensities.
The framework is demonstrated on an axisymmetric high-temperature exhaust plume reconstructed in three dimensions and analysed over a range of viewing directions. The results highlight the influence of plume morphology, projected emitting area, optical path length, and self-absorption on the angular dependence of the observed infrared radiation. To mitigate the computational cost of line-by-line calculations, the framework includes thermochemical clustering, spectral chunking, precomputed Planck functions, and line-of-sight geometry caching. These strategies enable practical multi-band and multi-angle analyses while preserving the high-resolution spectral description of the gas radiation.
Overall, the proposed framework provides a computationally efficient way to exploit high-fidelity line-by-line radiation modelling for plume analyses. This enables practical multi-band and multi-angle predictions while offering a modular foundation for future fully coupled CFD-radiation simulations, in which radiative source terms could be fed back into the flow solver.
Summary
A one-way CFD-to-radiation framework is presented for predicting infrared emission from high-temperature exhaust plumes. CFD-derived thermochemical fields are used to reconstruct the radiating gas domain and drive line-by-line radiative transfer calculations based on molecular spectroscopic databases. The emission–absorption equation is solved along multiple lines of sight to obtain spectral radiance, band-integrated intensities, and synthetic radiometric maps for different observation directions. The application to a reconstructed axisymmetric plume highlights how plume morphology, projected emitting area, optical path length, and self-absorption affect the observed infrared signature. Computational acceleration strategies enable practical multi-band and multi-angle analyses while preserving high-resolution spectral accuracy.