Simulation of a methane-air jet flame by les and rans model

A piloted methane/air jet flame, measured in the Sandia National Laboratory, is simulated by both 3-D large eddy simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) modeling. In LES, an algebra second order moment sub-grid scale (ASOM-SGS) combustion model is applied, while the second order moment (SOM) transport equation combustion model is employed in RANS method. The LES predicted time-averaged and root mean square (RMS) fluctuation temperature and methane concentration are in good agreement with the experimental data, showing the feasibility of the ASOM-SGS combustion model. For time-averaged temperature and species concentration, the performance of the RANS SOM model is rather good. Considering the difference of nearly two orders of magnitude in the computation time between LES and RANS modeling, the latter is considered to be more appropriate for engineering application. The LES instantaneous results show the coherent structures in the flame. It is found that reaction enhances the coherent structures, and conversely the coherent structures intensify combustion, forming a wrinkled-flame surface.