Capturing localised extinction in Sandia Flame F with LES-CMC

A Large Eddy Simulation (LES) using the Conditional Moment Closure (CMC) as a sub-grid turbulence-chemistry model has been applied to piloted jet diffusion flames (Sandia D&F). A 3D CMC grid was used which allowed different CMC boundary conditions to be applied in the jet and pilot streams. The code was found to give very good agreement with experiment in the low extinction case of Flame D. For Flame F transient extinction and re-ignition events were observed with LES–CMC which lead to reductions in averaged unconditional and conditional temperature consistent with experimental observations. Further analysis revealed that the CMC extinction/ignition events were the result of a combination of high conditional scalar dissipation rate and transport in the CMC grid.