Radiative Interactions in Thermochemical Nonequilibrium Expanding Flows

A numerical study is conducted to investigate radiative interactions in flows with thermal and chemical nonequilibrium. The two dimensional spatially elliptic Navier-Stokes equations have been used to numerically investigate different physical processes in the nozzle flow problem. The system of governing equations are solved using explicit, unsplit MacCormack predictor-corrector scheme. The chemistry source term is treated implicitly to alleviate stiffness associated with fast chemical reactions. Different physical processes considered in this study are investigated in a systematic manner. Finite chemical processes in chemically reacting supersonic nozzle flows are studied. Five hydrogen-air combustion models have been employed to study the influence of chemistry on flowfield and wall quantities. Truncated versions of different chemistry models are used to identify the effect of different chemical species and reaction paths. Further, extensive parametric studies are conducted to investigate the effects of equivalence ratio and inlet Mach number on the flowfield characteristics as well as on wall heat flux. Combustion of hydrogen-air results in highly absorbing-emitting gases such as water vapor, OH and NO radicals. The effect of radiative interactions has been studied through application of a gray gas model. Results indicate that choice of chemistry model is an important issue. Based upon the understanding of chemical nonequilibrium and radiative interactions, thermal nonequilibrium phenomena are investigated. Furthermore, radiative interactions are included in this problem. Also for basic understanding of the radiative interaction, a simple problem is used to investigate effects of radiative energy transfer in incompressible flows under the assumption of local thermodynamic equilibrium (LTE) and non-local thermodynamic equilibrium (NLTE). Results indicate that both chemical and thermal nonequilibrium effects are important in the expansion region of the nozzle. The effect of radiative interactions is to reduce the extent of thermal nonequilibrium due to additional mode of energy transfer