Unsteady-state simulation of model ram accelerator in expansion tube

Steady- and unsteady-state numerical simulations have been carried out to i nvestigate the ram accelerator flowfield that had been studied experimental ly using an expansion tube facility at Stanford University. Navier-Stokes e quations for chemically reactive flows were used for the modeling with a de tailed hydrogen-air combustion mechanism. The governing equations were anal yzed using a fully implicit and time-accurate total variation diminishing s cheme. As a result, steady-state simulation reveals that the near-wall comb ustion regions are induced by aerodynamic heating in the separated flow reg ion. This result agrees well with experiments in the case of the 2H(2) + O- 2 + 17N(2) mixture but fails to reproduce the centerline combustion in the case of the 2H(2) + O-2 + 12N(2) mixture. To investigate the reason for thi s disagreement in the flow establishment process, unsteady-state simulation s have been carried out, and the results show the detailed process of flow stabilization. The centerline combustion is revealed to be an intermediate process during flow stabilization. It is induced behind a Mach stem formed by the intersection of strong oblique shock waves at an early stage of the flow stabilization process. This primary combustion zone is sustained for 3 0 and 40 mu s respective to the mixtures and completely disappears later. T he overall time needed for flow stabilization is about 150 mu s, and the st eady-state result is recovered.