Complex Wall Injector Array for Scramjet Combustors

This paper presents the results of experimental and numerical studies of an array of injectors combining inclined, circular and diamond-shaped, sonic nozzles for application to high-Mach-number scramjets with light-gas fuels. The freestream Mach number was 4, and Helium was used as the injectant to safely simulate Hydrogen fuel. The diamond injector provided improvements in penetration of more than a factor of two compared to the circular injectors. This is a much greater increase than had been inferred earlier by comparing test results with isolated diamond and circular injectors. The rate of mixing as indicated by the decay of maximum concentration in the plume was about the same. CFD with a RANS formulation was applied to this flow problem with four different turbulence models. The helium mixing predictions from the four turbulence models, showed that the simulations are heavily impacted by the turbulence model selection. None of the turbulence models were able to accurately simulate the helium mixing shown in the experiment, but some models did much better than others. From the selected models, the k-ω model by Wilcox had the best correlation with the experimental helium concentration profiles. The CFD solutions were also probed to elucidate the behavior of the flow in the plumes from the circular and diamond injectors. From a design point-of-view, these results show that it is useful to combine inclined diamond and circular injectors to achieve good fuel coverage and fuel/air mixing across a scramjet combustor.