Investigation of the flamelet method for transcritical/supercritical combustion in rocket engines

<p indent="0mm">The chamber pressure of high-thrust liquid rocket engines typically far exceeds the thermodynamic critical pressure of the propellants, resulting in considerable transcritical and supercritical effects during propellant mixing and combustion. Because of the technical challenges associated with high-pressure combustion experiments, flamelet-based combustion simulations have become a key technology for understanding the transcritical and supercritical turbulent combustion processes within combustion chambers. Although the accuracy of the flamelet method under subcritical conditions has been validated, its predictive performance under transcritical and supercritical conditions still requires further evaluation. To this end, this study focuses on trans and supercritical hydrogen-oxygen combustion in rocket engines. Under transcritical and supercritical laminar combustion conditions, <italic>a priori</italic> and <italic>a posteriori</italic> analyses of the flamelet method were conducted by comparison with direct numerical simulation (DNS). The results demonstrate that the flamelet method can accurately predict temperature, species concentrations, and other thermodynamic quantities for transcritical and supercritical hydrogen-oxygen combustion. Compared with DNS, the flamelet method considerably improves computational efficiency. Furthermore, for a typical multinozzle hydrogen-oxygen rocket engine combustion chamber, the flamelet method was applied to conduct three-dimensional large-eddy simulations of turbulent combustion with complex geometries. The results indicate that the flamelet method accurately captures turbulent flame structures, with flames forming and stabilizing at the nozzle lips. As the flames develop downstream in the combustion chamber, the temperature progressively increases, although a certain degree of incomplete combustion remains.