Numerical simulation of oxy-fuel jet flames using unstructured LES-CMC

A finite volume Conditional Moment Closure (CMC) formulation has been developed as an LES sub-grid combustion model. This allows unstructured meshes to be used for both LES and CMC grids making the method more applicable to complex geometry. The method has been applied to an oxy-fuel jet flame. This flame offers new challenges to combustion modelling due to a high CO2 content in the oxidiser stream and significant H2 content in the fuel stream. The density ratio of the two streams is of the order 5 and the viscosity of the two streams will also differ. All the flames simulated showed localised extinction in the region around 3-5 jet diameters downstream of the nozzle, which is in very good agreement with the experiment. Trends for conditional and unconditional statistics with changing levels of H2 in the fuel are correctly captured by the LES-CMC method, although different levels of agreement are observed for different species and temperature and possible reasons for this are discussed. The degree of extinction is also correctly predicted to increase as the H2 content of the jet is reduced, showing the ability of the CMC method to predict complex turbulence-chemistry interaction phenomenon in the presence of changing fuel composition.