An improved CO₂, H₂O and soot infrared radiation models for high temperature flows

A versatile computer model for calculating the infrared radiation of soot and H₂O and CO₂ molecules in generic flowfields is proposed and examined. These radiators are often the major sources in combustion and atmospheric flows, yet most existing programs do not accurately model them. Molecular radiation is calculated using the HITRAN/HITEMP and CDSD-1000 line-by-line databases to provide high-resolution, accurate spectra between 200 and 8200 cm^-1. The internal partition functions and state energies are divided into rotational and vibrational components to incorporate non-local thermal equilibrium conditions. Soot particulates are assumed to be spherical; therefore, their radiation is modeled using the first-term approximation of Mie scattering theory. Because the particles are small compared to the wavelengths modeled, it is possible to neglect scattering in the pseudo-gas approximation. The program was parallelized in spectral increments to run efficiently on an MPI-equipped cluster. Local thermal equilibrium results for H₂O and CO₂ were compared against the ATHENA radiation model. Additionally, the program was modified to model CO radiation to make a direct non-local thermal equilibrium comparison with NEQAIR-IR. Soot radiative properties were validated against measurements made on a sooting diffuse laminar flame. The completed program is applied to two situations: a non-equilibrium bow shock generated by a sounding rocket and a sooting plume from an Atlas rocket. Analysis of the bow shock spectrum at 40 and 50 km shows that H₂O and CO₂ are the predominant radiators. NO contributes approximately 10 percent of the total intensity at 40 km while other radiators are less than .1 percent as bright as the triatomic molecules. The overall intensity is lower at 50 km than it is at 40 km because of the reduced atmosphere.