Direct Numerical Simulation of a Turbulent Lifted Flame: Stabilisation Mechanism

A turbulent lifted slot-jet flame is studied using direct numerical simulation (DNS). A single step chemistry model is employed with a mixture-fraction dependent activation energy to quantitatively reproduce the dependence of laminar burning rate on equivalence ratio that is typical of hydrocarbon fuels. It is observed that the leading flame edge exhibits a single branch close to the stoichiometric mixture fraction iso-surface, rather than a tribrachial structure. The flame edge has a complex, highly convoluted structure suggesting it can burn at speeds that are much faster than SL. There is no evidence of a rich inner premixed flame or detached diffusion flame islands, in contrast with the observation in the previous DNS studies of hydrogen flames. On average, the streamwise velocity balances the streamwise flame propagation, confirming that flame propagation is the basic stabilisation mechanism. The analysis of the flow and propagation velocities reveal an elliptical pattern of flame motion around the average stabilisation point. Visualisation of the flame suggests that this motion is connected with the passage of large eddies.