Cavity enhanced jet interactions in a scramjet combustor

Abstract

The shock structure around a fuel jet drives most of the initial mixing in a scramjet combustor, making it of interest for mixing enhancement studies. The effect of a cavity placed upstream of a fuel injector on the jet interaction of a transverse jet in a supersonic crossflow was examined numerically in this work. The cavity was found to significantly alter the structure of the typical supersonic cross-flow jet interaction. The typical horseshoe vortices were found to be absent and the barrel shock was found to be larger and more upright than in the no-cavity case. This was caused by the cavity recirculation shielding the fuel jet. The shock structure around the cavity was found to decrease the strength of the bow shock, reducing total pressure loss in the flowfield close to the injector. A small region of fluid above the cavity circulation was found to be the origin of vortical structures in the jet interaction, as opposed to the wall boundary layer in the conventional jet interaction. The presence of the fuel jet was found to alter the flow behaviour inside the cavity from closed cavity flow to open cavity flow, with the recirculation rising out of the cavity. This transition from closed to open cavity flow was found to be turbulence model dependent, however the main flow features and behaviour were shown to be maintained across turbulence models. Fuel was entrained in the cavity for the configuration under investigation, however this was dependent on fuel injection pressure, with no fuel entering the cavity at lower injection pressures.