Flow establishment in a generic scramjet combustor

The establishment of a quasi-steady flow in a generic scramjet combustor is studied for the case of a time varying inflow to the combustor. Such transient flow is characteristic of the reflected-shock tunnel and expansion-tube test facilities. Several numerical simulations of hypervelocity flow through a straight-duct combustor with either a side-wall-step fuel injector or a centrally-located strut injector are presented. Comparisons are made between impulsively started but otherwise constant flow conditions (typical of the expansion tube or tailored operation of the reflected-shock tunnel) and the relaxing flow produced by the 'undertailored' operation of the reflected- shock-tunnel. Generally the inviscid flow features, such as the shock pattern and pressure distribution, were unaffected by the time varying inlet conditions and approached steady state in approximately the times indicated by experimental correlations. However, viscous features, such as heat transfer and skin friction, were altered by the relaxing inlet flow conditions.