Application of k-distribution method to molecular radiation in hypersonic nonequilibrium flows

In typical earth reentry conditions, high-temperature gases in the shock-layer are highly dissociated, and molecular radiation radiation is comparatively weaker than atomic radiation. Even for conditions where molecular radiation is significant, it is optically thin, and most of it escapes from the shock layer. For typical flow conditions molecular radiation problems can be solved quite accurately by making the gray approximation. One such calculation is presented for the stagnation line flow field of the Crew Exploration Vehicle (CEV). For other cases, when molecular radiation is not optically thin, there may be significant absorption of incoming and locally emitted energy. For such cases, the gray approximation results in significant error. The k-distribution method for an isolated molecular band in nonequilibrium hypersonic flow is presented. Both the correlated-k and the scaling approximation approaches are discussed, and heat transfer results are compared with line-by-line bench marks and gray calculations. Schemes for dividing the full spectrum into a number of part-spectra are presented, together with the achieved improvement in accuracy of the k-distribution method.