Large Eddy Simulation Of Multi-regime Flames With FGM Method

Turbulent combustion process is widely encountered in power generation systems, such as aircraft automobile engines, power station boilers. The process of turbulent combustion can be classified into three regimes by the mixing state of the fuel and the oxidizer:diffusion combustion (non-premixed combustion), premixed combustion and partially premixed combustion. Diffusion combustion and premixed combustion is two ultimate limit states of combustion, which are often existed simultaneously in turbulent combustion fields. Numerical investigation for such a multi-regimes turbulent combustion process with simply one of the premixed combustion model or non-premixed combustion model will certainly reduce the precision of the results.In the present researches, a combustion model based on the FGM method was built to simulate the multi-regimes turbulent combustion and subsequently the large eddy simulation was carried out with this model.Firstly, one-dimensional laminar non-premixed and premixed flames were calculated with OPPDIF and PREMIX program, respectively. The complex chemical reaction space was projected onto low-dimensional space with FGM method to simplify the chemical reaction in the combustion process to reduce the dimension of the computation. Then the laminar FGM premixed/non-premixed table can be obtained. To consider the influence of the turbulence effect on laminar flame, assuming that the scalars which can characterize the reaction field in laminar FGM premixed/non-premixed table obey Beta distribution function, so Beta-PDF was introduced to calculate the turbulent FGM premixed/non-premixed table. Finally, the flame index which was used to judge the premixed and non-premixed region together with the multi-FGM table, namely multi combustion model, was introduced into large eddy simulation to calculate the diffusion flame carried out by Combustion Laboratory of the University of Sydney.The results predicted by the multi-regimes combustion model showed that the flame index can correctly judge the premixed and non-premixed region. Simultaneously the model can well predict the flow field and reaction field. It is obvious that the distribution of the temperature and mass fraction of species predicted by multi combustion model fit well with the experiment datum, especially shows its advantages on prediction of productions of reaction when compared with the results calculated by FGM non-premixed model.