抄録
Large eddy simulation (LES) of turbulent premixed combustion is carried out in the present study. A flamelet model based on the G-equation is used as a combustion model of premixed flames. In the context of LES, the turbulent burning velocity (ST) is required to obtain a closed form of the G-equation. Unfortunately, the turbulent burning velocity is not a well-defined quantity and the scatter of experimental data is very large, so that no universal model is available for ST. Hence, two models of ST, which are considered to be the most standard at present, are compared to investigate their influence on the configuration of the premixed flames through LES. In addition to the lack of its predictability, ST is generally modeled by experimental fits of the mean turbulent burning velocity in Reynolds aver-aging context. In conducting LES, the root-mean-square velocity fluctuation must be replaced with the subgrid-scale (SGS) velocity fluctuation, which has close relation to a SGS model for turbulent motion. Therefore, we also examine the influence of two SGS models on the flame configuration. The SGS models to be compared here are the Smagorinsky model and the structure-function model. To carry out the numerical investigation, we consider a simple model combustor with a cylindrical premixer and a rectangular combustion chamber, where a simple premixed hydrogen-air jet flame is stabilized in a backward-facing step without swirling. Through the present LES, it is shown that the numerically predicted configuration of the premixed flame depends strongly upon the model equations of the turbulent burning velocity and upon the SGS models for turbulence.
