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Large Eddy Simulation of MILD combustion using PDF based turbulence-chemistry interaction models

The present work reports on LES of turbulent reacting flow of the Delft-Jet-in-Hot-Coflow (DJHC) burner, emulating MILD combustion, with transported PDF based combustion models using ANSYS FLUENT 13.0. Two different eddy viscosity models for LES (Dynamic Smagorinsky and Kinetic Energy Transport) along with two solution approaches for PDF transport equation, i.e. Eulerian and Lagrangian, have been used in the present study. Moreover, the effects of chemical kinetics and the micro-mixing models have also been investigated for two different fuel jet Reynolds number (Re = 4,100 and Re = 8,800). The mean velocity and turbulent kinetic energy predicted by the different models are in good agreement with experimental data. Both the composition PDF models predict an early ignition resulting in higher radial mean temperature predictions at burner exit. The models, however, correctly predict the formation mechanism of ignition kernels and the decreasing trend of the lift-off height with increasing jet Reynolds number, as observed experimentally.