Direct numerical simulation of inflow boundary-layer turbulence effects on cavity flame stabilisation in a model scramjet combustor

Abstract

Supersonic lean premixed hydrogen/air combustion stabilised by a cavity-flame holder within a model scramjet, characterized by a Mach 1.5 inflow at 1000 K and 50 kPa, is investigated via direct numerical simulation. By separately implementing wall-bounded turbulent and laminar inlet conditions, this work analysis various physical processes of flame stabilization and turbulence-flame interactions to study the influence of inflow boundary layer conditions. Findings indicate that combustion occurred within the cavity shear layer in both cases and propagated downstream along the lower wall. Also, the server impingement at the rear wall in the case with laminar inflow leads to greater cavity resistance. Furthermore, the studies on gas exchange and transport process indicates that with laminar inflow the entered gas accumulates in the back part of the cavity via the intensive mass exchange process and weaker interaction between the primary and secondary vortices. Flame stretch and thickness are further investigated to shed light into turbulence-flame interaction in supersonic flows. Findings indicates that the case with inflow wall-bounded turbulence show similar behaviours compared to previous studies, whereas the observed phenomena in front part of cavity shear layer are differ due to the presence of roll-up vortices in the case with laminar inflow. Overall, the influence of tangential strain rate and curvature are consistent with the preceding results and the evolution of flame thickness is caused by the combined effect of the two factors in both cases.