Isolator Dynamics During Unstart of a Dual-Mode Scramjet

Abstract

The phenomenology of unstart in a dual-mode ethylene-fueled scramjet is studied in the presence of inflow distortion using carefully calibrated unsteady Reynolds-averaged Navier–Stokes computations with an emphasis on understanding the large-scale transients over the length scale of the flowpath. The computational approach is validated with experimental data for two combustor operating states that bound the dual-mode and unstart conditions. Unstart is induced via an imposed fuel-staging transient that emulates the experiments. Inlet distortion introduces three-dimensional effects in the isolator, which primarily manifest in the nature of side wall separation and flow curvature; however, localized regions of heat release are shown to contribute to unstart-inducing side wall separation. A wall-pressure-based metric used to track shock-train motion in experiments is adapted to identify a period of constant shock-train speed and an incipient unstart condition. During the constant-velocity phase, separation on the upper wall modulates the supersonic core, resulting in a change from an oblique to a normal-like shock-train configuration. The incipient unstart state precedes the ejection of the shock train from the isolator, which is suggestive of a precursor to unstart. This metric highlights the importance of the side wall corner region during the unstart process and complements other studies of three-dimensional effects in similar isolator geometries.