Mode transition and combustion characteristics of a dual-mode scramjet engine using flamelet modeling

This study presents a numerical investigation of mode transition and combustion characteristics in a dual-mode scramjet engine, employing a compressible flamelet/progress variable (CFPV) model coupled with a self-adaptive turbulence eddy simulation (SATES) approach. The flamelet tables were generated for a methane/ethylene/air mixture using the Gas Research Institute 3.0 chemical mechanism. A mixture-fraction-dependent lookup table was incorporated to rescale the source term of progress variable, thereby accounting for the pressure effects. Steady Reynolds-averaged Navier–Stokes simulations against experimental measurement from a strut and a cavity model combustor confirm that the present CFPV model yields more accurate predictions of wall pressure, flame topology, and heat release distribution than the conventional uncorrected flamelet/progress variable model. Detailed SATES simulations were performed at flight Mach numbers of 5.8 and 6.5 to resolve the inherent mode transition characteristics. The transition process from the ramjet to scramjet mode was well captured as the inflow Mach number and overall equivalence ratio increase, which was accompanied by a shift in the flame stabilization mechanism from a jet-wake stabilized to a cavity-assisted jet-wake flame mode. Further statistical analyses distinguish variations in turbulent combustion regimes and premixed/diffusion flame proportions under different operating conditions, and transient shock-induced auto-ignition events inside the jet-wake region are reasonably reproduced by the proposed numerical approach.