Direct Numerical Simulations of O_2/H_2 Temporal Mixing Layers Under Supercritical Conditions

Direct numerical simulations of a supercritical oxygen/hydrogen temporal three-dimensional mixing layer are conducted to explore the features of high-pressure transitional mixing behavior. The conservation equations are formulated according to fluctuation–dissipation theory and are coupled to a modified Peng–Robinson equation of state. The boundary conditions are periodic in the streamwise and spanwise directions and of nonreflecting outflow type in the cross-stream direction. Simulations are conducted with initial Reynolds numbers of 6 x 10^2 and 7.5 x 10^2, initial pressure of 100 atm, and temperatures of 400 K in the O_2 and 600 K in the H_2 stream. Each simulation encompasses the rollup and pairing of four initial spanwise vortices into a single vortex. The layer eventually exhibits distorted regions of high density-gradient-magnitude similar to the experimentally observed wisps of fluid at the boundary of supercritical jets. Analysis of the data reveals that the higher-Reynolds-number layer reaches transition, whereas the other one does not. The transitional layer is analyzed to elucidate its characteristics