A numerical study of high-pressure oxygen/methane mixing and combustion of a shear coaxial injector

The mixing and combustion of cryogenic oxygen and methane in a shear coaxial injector operating under supercritical pressures are investigated numerically. The formulation accommodates full conservation laws and real-fluid thermodynamics and transport phenomena. The near-field fluid injection and mixing dynamics are characterized by the evolution of two mixing layers. The vigorous fluctuations generated from the inner mixing layer, which consists a string of large scale vortices emerging from the LOX post tip, provide a forcing on the outer shear layer. The formations of large structures do not follow the fundamental Kelvin-Helmholtz instability mechanism, but in a manner analogous to that produced at a backward-facing step. The effect of the momentum-flux ratio on the flow evolution is demonstrated. As the velocity of the methane stream increases, turbulent mixing is enhanced, and both the inner and outer potential cores are reduced. A diffusion dominated combustion occurs in the presence of large gradient of fluid properties. The work also identifies the flame anchoring mechanism.