Effects of near wall flow and non-equilibrium reaction coupling on heat flux prediction inside a 7-elements GOX/GCH4 combustion chamber

Methane/oxygen rocket engine is considered to be one of the most promising reusable rocket engines in future space activities. Adequate understanding and accurate prediction of heat transfer characteristics are considered key points for the development of reliable methane engines. In this paper, a methane combustion chamber with 7-elements is simulated using Reynolds averaged Navier-Stokes (RANS) method with Eddy Dissipation Concept (EDC) combustion model. The investigation reveals that the near-wall coupling effects of flow and chemistry have a significant influence on the wall heat load, and the coupled wall function developed by direct numerical simulation (DNS) is modified, validated, and incorporated in the RANS frame to consider the aforementioned coupling effects. The results show that the deviation of the wall heat load compared to experimental data is reduced from 25% to 5% for the wall of high temperature when chemistry effects are considered. The influence of the coupled wall function is limited near the wall and the properties of main flow are generally independent of the wall models adopted. The investigation also reveals that the turbulent flux of chemical enthalpy near the wall is comparable to the turbulent flux of sensible enthalpy in case of a methane combustion chamber. Finally, the effects of chemistry on the wall heat flux can be attributed to the coupling impacts of the chemical equilibrium shifting caused by the large temperature gradient near the wall and the non-uniform radial velocity brought by the powerful vortex system in the chamber.