Effects of mixing localisation in LES-MMC simulations of a lifted hydrogen flame

This work presents sparse-Lagrangian simulations of a lifted hydrogen flame in a vitiated coflow of combustion products. An Eulerian Large Eddy Simulation generates turbulent flow field data including filtered velocity, density and a reference mixture fraction. A sparse ensemble of notional Lagrangian particles is then used to solve the Filtered Density Function for the subgrid reactive scalar quantities. A Generalised Multiple Mapping Conditioning (MMC) micro-mixing model enforces local mixing in extended space which comprises of physical space and the LES simulated reference mixture fraction. Predictions of lift-off, stabilisation and turbulent composition are obtained with as few as 23,000 Lagrangian particles while 1.9 million grid cells are used for the Eulerian LES. Lift-off height predictions are sensitive to the coflow temperature and the degree of mixing localisation. Excessive localisation in mixture fraction space or high coflow temperatures results in flame attachment while less localisation or low temperatures causes flame extinction