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Multi-group reductions of LTE air plasma radiative transfer in cylindrical geometries

par Scoggins, James Brice;Magin, Thierry ;Wray, Alan;Mansour, Nagi N.N.
Référence 44th AIAA Thermophysics Conference(44: 2013-06-24), American Institute of Aeronautics and Astronautics Inc
Publication Publié, 2013

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Résumé :

Air plasma radiation in Local Thermodynamic Equilibrium (LTE) within cylindrical geometries is studied with an aim towards modeling the radiative transfer inside arc-constrictors, a central component of constricted-arc arc jets. A detailed database of spectral absorption coefficients for LTE air is computed using the NEQAIR code developed at NASA Ames Research Center. The database stores calculated absorption coefficients for 1,051,755 wavelengths between 0:04 μm and 20 μm over a wide temperature (500K to 15 000K) and pressure (0:1 atm to 10:0 atm) range. The multi-group method for spectral reduction is investigated by generating a range of reductions including pure binning and banding reductions from the detailed absorption coefficient database. The accuracy of each reduction is compared to line-by-line calculations for cylindrical temperature profiles resembling typical profiles found in arc-constrictors. It is found that a reduction of only 1000 groups is sufficient to accurately model the LTE air radiation over a large temperature and pressure range. In addition to the reduction comparison, a cylindrical-slab formulation is compared with a finite-volume method for the numerical integration of the radiative flux and energy source term inside cylinders. By varying the ratio of the cylinder length to its radius, it is determined that the cylindrical-slab approximation can be used to adequately model arc-constrictors with large length to radius configurations.