PHYSICS OF METHANE COMBUSTION IN MIXING SHEAR-LAYER

A 2-dimensional numerical analysis of unsteady diffusive combustion wi th methane as the fuel and oxygen as the oxidizer was performed, focus ing on (a) the physics of complicated mixing and combustion, and (b) t he influence of heat release on mixing. The computational domain is a square surrounded by (i) adiabatic and free-slip boundaries, and (ii) flux-periodic boundaries. Each of nitrogen-diluted methane and nitroge n-diluted oxygen is injected with Reynolds number 1,000 from a periodi c boundary to the opposite direction, where (a) the upper right-going high-temperature methane layer and (b) the lower left-going high-tempe rature oxygen layer interact and get mixed due to vortical entrainment and molecular diffusion. Applying the direct numerical simulation (DN S) method (second-order accurate in time, fourth-order in space, and m aximum mesh Reynolds number=15) to such a temporally-growing counter s hear layer, important information characterizing the reactive mixing l ayer, such as temporal change of vortex structure due to heat release, is obtained. At an early stage of vortical structure change, initiall y-existing 2 large-scale vortices, which correspond to the fundamental perturbation frequency, split into 4, due to thermal expansion and ba roclinic effect. At a later stage, however, the baroclinic effect with in the reaction zone plays a dominant role to promote the structure ch ange, locally intensifying or weakening the vorticity.