Investigation on the mode transition of a typical three-dimensional scramjet combustor equipped with a strut

A three-dimensional compressible Reynolds-averaged Navier-Stokes (RANS) equations coupled with the two equation RNG k-epsilon turbulence model have been employed to capture the mode transition properties in a dual-mode scramjet combustor. Based on the code validation and the grid independency analysis, two transition processes from scram to ram mode and from ram to scram mode are analyzed in detail. The fuel equivalent ratio is controlled by linearly increasing or decreasing the injection pressure of each nozzle to achieve the mode transition. During the mode transition, the thermodynamic properties of the combustion chamber change dramatically and the flow field structure changes correspondingly. The variation of the flow field structure is mainly reflected in the upstream flow field, while the variation of the flow field temperature is mainly reflected in the downstream flow field. The obtained results show that there is an obvious temperature variation in the downstream flow field. Besides, the upstream wave structures will change when the temperature varies to a certain degree, then the mode-transition occurs completely. Since the ram mode is a more stable mode than the scram mode, and the transition to the scram mode is more difficult than the transition from the scram mode to the ram mode. The variation of the shock wave position in the isolator is accompanied by the variation of the mode transition. During the transition from scram to ram mode, the shock wave at the combustor entrance is gradually pushed out and moves forward at the position with the lowest Mach number. During the transition from ram to scram mode, the shock wave in the isolator is gradually pushed forward into the flow field, but the shock waves is still in the isolator when the flow field turns into the scram mode. (C) 2020 Elsevier Ltd. All rights reserved.