Jean-Etienne DURAND, Frédéric OLIVON
DOI Number: XXX-YYY-ZZZ
Conference number: HiSST 2024-00130
Beyond the flight Mach number 7, the scramjet, with supersonic combustion, shows higher performances than the ramjet, with subsonic combustion, due to the substantial pressure losses, chemical dissociation effects, and high thermomechanical stresses. The dual-mode scramjet would be a solution to hold optimal performances over an extensive range of flight Mach numbers. The use of a divergent nozzle choked through a thermal throat, generated by heat combustion, turns out to be an elegant approach to switch from subsonic to supersonic combustion processes, avoiding mechanical constraints and complex systems. Furthermore, compared with conventional ramjet, this approach increases the allowable mass flow rate through the engine, increasing the thrust. However, even though the model can use only Euler equations, several phenomena, such as the boundary layer and the combustion heterogeneity, could significantly affect the throat shape and position and, therefore, the propulsive performance, in ramjet mode. The present work aims to study the effect of the boundary layer on the thermal throat section characteristics and the related engine performance. A 1D steady model of a thermally choked nozzle (TCN) is developed to improve the 1D model of a dual-mode scramjet. A boundary layer model is introduced to take into account its effects on the position and the area of the thermal throat section. Numerical simulations, computed with CEDRE, the ONERA CFD software, will be carried out to validate the obtained results in the 1D model. The consideration of the boundary layer effects in the TCN leads to a significant shift of the thermal throat position toward the inlet and must be taken into account for the performance assessment of thermally choked engines.