Simulations of scramjet starting and establishment time in an expansion tunnel

A "nose to tail" numerical simulation is used to demonstrate that steady flow can be achieved through a complete scramjet model in an expansion tunnel. For this study, a numerical simulation was undertaken for a single condition of interest from the X2 expansion tunnel, using an un-fueled combustor. The results from the facility simulation matched reasonably well with experimental measurements and the simulated exit flow of the expansion tunnel was then used as a transient inflow boundary condition into a scramjet simulation. The results from the scramjet simulations showed that, for the studied variables, the inlet started in a relatively short period. Further into the duct, unsteady inflow from the expansion tunnel simulations resulted in some movement of the wave pattern over time. To obtain an estimate of establishment time that was somewhat insensitive to small movements in the wave pattern, a new flow variable was constructed by integrating the normalized pressure distribution over short lengths of duct. This measure was then used to show that the scramjet would reach quasi-steady flow after 350 μs and would have a test period of 200 μs.