Analysis and calculation of chemical non-equilibrium turbulent flow in a scramjet nozzle

In this paper, 7-species, 8-step finite-rate chemical reaction models of the non-equilibrium flow in a scramjet single expansion ramp nozzle have been investigated numerically. Chemical reactions and mass transfer under various freestream Mach numbers and flight height conditions are performed by the RNG k-ε turbulence model. The fluid flow in the nozzle is analyzed under non-equilibrium chemical reactions and frozen flow conditions. It is shown that the total temperature is obviously increased while the total pressure is evidently decreased in the chemical non-equilibrium flow at certain inlet conditions. The mass fractions of H₂ and O₂ are decreased while that of H₂O is increased, and the mass fraction of N ₂ is almost identical throughout the whole reaction process. This indicates that combustion occurs in the nozzle, and the scramjet nozzle can supplement the combustion in a supersonic combustor so that the performance of the nozzle can be increased. It can be found that there are eddies in the chemical non-equilibrium flow because of the variations of the mass fractions of O₂, H, O and OH. These eddies suggest that the variations of the mass fractions of O₂, H, O and OH is non-monotonic. Although the flow is speeded up, the chemical reaction at the beginning part of the nozzle is faster than that downstream. The calculation shows that the non-equilibrium chemical reactions should always be considered in investigations of the flow and performance of scramjet nozzles.