Steady and unsteady numerical simulations are conducted for the experiments performed to investigate the ram accelerator flow field by using hte expansion tube facility in Stanford University. Navier-Stokes equations for chemically reacting flows are analyzed by fully implicit time accurate numerical method with Jachimowski's detailed chemistry mechanism for hydrogenair combustion involving 9 species and 19 reaction steps. Although the steady state assumption shows a good agreement with the experimental schilieren and OH PLIF images for the case of 2H_2+O_2+17N_2, it fails in reproducign the combustion region behind the shock itnersection point shown in the case of 2H_2+O_2+12N_2 mixture. Therefore, an unsteady numerical simulation is conducted for this case and the result shows all the detailed flow stabilization process. Teh experimental result is revealed to be an instantaneous result during the flow stabilization process. The combustion behind the shock intersection point is the result of a normal detonation formed by the intersection of strong oblique shocks that exist at early stage of the stabilization process. At final stage, the combustion region behind the shock intersection point disappears and the steady state result is retained. The time required for stabilization of the reacting flow in the model ram accelerator is found to be very long in comparison with the experimental test time.
展开▼
