Velocity-driven optimization of film cooling in methane/oxygen rocket engines using coupled wall function

Abstract

This study investigates the application of coupled wall functions to the research of film cooling in methane/oxygen rocket engine combustion chambers. By manipulating film mass flow rate and inlet size, the influence of different film-mainstream velocity ratios on flow dynamics, combustion, wall heat transfer, and cooling efficiency within the combustion chamber is explored. Results indicate that as the ratio of film velocity to mainstream velocity (R_V) increases, the combustion chamber pressure initially decreases before increasing, with a corresponding trend observed in vortex intensity at the inlet section. Comparative analysis reveals that, while maintaining a constant mass flow rate, reducing the film inlet height results in lower pressures and weaker swirl strength. Furthermore, wall heat transfer decreases gradually with increasing R_V, with lower heat transfer observed in cases involving additional low-temperature methane injection. Notably, the introduction of coupled wall functions minimally impacts mainstream flow and combustion. Analysis of Net Heat Flux Reduction (NHFR) indicates a rapid decrease in cooling efficiency in the front half of the combustion chamber, emphasizing the suitability of employing a film cooling inlet every one-fifth section in a methane/oxygen engine. Moreover, increasing the mass flow rate enhances cooling efficiency as R_V increases, while altering the inlet size yields nearly constant cooling efficiency. Therefore, maximizing film mass flow rate is deemed preferable for film cooling arrangements in a specific rocket engine; however, comparative studies reveal a gradual reduction in engine specific impulse with increasing mass flow rate, underscoring the necessity for engine-specific determinations.