Topological analysis of methane lean premixed flame in turbulent jet flow by direct numerical simulation

Abstract

Direct numerical simulation is employed to investigate the premixed jet flame of methane in lean, combined with a detailed chemical kinetics including 17 species and 58 elemental steps and distinct Lewis numbers. Cold methane-air mixture at 0.55 equivalence ratio is injected into the coflow area with 9500 Reynolds number. The coflow ambient gas is set to be the burnt gas of the methane-air mixture in main jet and temperature is assigned to be the corresponding adiabatic flame temperature 1515 K. The whole simulation process is run based on paralleled calculation method, and chemical sources are acquired by dynamically calling CHEMKIN library function. The flame structure at 6.98 ms is shown to demonstrate the obvious dependence of flame structure and reaction rate on vortices motion. Then by tracing the interaction between different flame elements and vortices, the mechanism behind this dependence is found. The concepts including surface density function, mean curvature and stretch rate are used to describe the geometrical structure of vortex-affected flame. Those are all calculated according to simulation result and statistically associated with heat release rate that indicates reaction intensity. The statistical results show that surface density function and reaction rate own direct positive correlation; largely wrinkled flames with greater curvatures magnitude tend to become thick and weaken surface density function and reaction rate, appearing local extinction phenomena; large tangential stretch rates exerted on flame usually produce a local thinning effect in normal making reaction rate intensified. The DNS presented will supply beneficial references to better understanding of flame-vortex interaction and development of more accurate general model for turbulent premixed combustion.