Simulation of unsteady hypersonic combustion around projectiles in an expansion tube

The temporal evolution of combustion flowfields established by the interact ion between wedge-shaped bodies and explosive hydrogen-oxygen-nitrogen mixt ures accelerated to hypersonic speeds in an expansion tube is investigated. The analysis is carried out using a fully implicit, time-accurate, computa tional fluid dynamics code that we recently developed to solve the Navier-S tokes equations for a chemically reacting gas mixture. The numerical result s are compared with experimental data from the Stanford University expansio n tube for two different gas mixtures at Mach numbers of 4.2 and 5.2. The e xperimental work showed that flow unstart occurred for both the Mach 4.2 ca ses, These results are reproduced by our numerical simulations and, more si gnificantly, the causes for unstart are explained. For the Mach 5.2 mixture s, the experiments and numerical simulations both produced stable combustio n. However, the computations indicate that in one case the experimental dat a were obtained during the transient phase of the flow; that is, before ste ady state had been attained.