Numerical investigation of the scale effects of the flame flashback phenomenon in scramjet combustors

Abstract The scale effect of flame flashbacks inside an ethylene-fueled scramjet combustor was investigated through an approach that combines numerical, experimental, and theoretical analyses. In the current study, a hybrid large eddy simulation (LES)/flamelet-progress variable (FPV) combustion model was compared with experimental observations and measurements, and a good level of agreement was shown. As the scale changed, the boundary-layer profiles showed differences to some extent. A larger-scale engine could obtain higher fuel mixing efficiency and thus had the potential to yield intense combustion, enhancing the downstream backpressure and boundary-layer separation. The gradually separated boundary layer formed a quick thermally choked flow, prompting the flame front to accelerate forward until it was transmitted back to the fuel injection position. The low-speed zone in the interior of the boundary layer was more conducive to combustion enhancement and the formation of positive feedback. In addition, the simplified flame flashback model combined with the flame stabilization model was used to illuminate the scale effects of flame flashback.