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为了研究湍流扩散火焰的燃烧特性和局部熄火现象的机理,使用火焰面/反应进度模型对Sandia湍流值班射流火焰E进行大涡模拟。火焰面/反应进度模型适用于非预混燃烧,基于守恒标量和反应标量构建火焰面数据库,将详细的化学反应过程映射到这两个特征标量的平面上。数值模拟结果与实验数据符合得较好,火焰面/反应进度模型能较好地模拟湍流扩散火焰和预测火焰的不稳定性。研究发现,火焰在轴向距离与中心射流直径比值为7.5至15的截面处局部熄火概率较大,这与该位置标量耗散率偏大有关;火焰在轴向距离与中心射流直径比值为30以后的流场重新点燃,原因是混合物分数和当量比变小,火焰更多处于贫燃状态。
In order to study the combustion characteristics of turbulent diffusion flame and the mechanism of local flameout, a large eddy simulation of Sandia turbulent on-stream flame E was carried out by using the flame surface / reaction progress model. The flame surface / reaction progress model is suitable for non-premixed combustion, building a flame surface database based on conservation scalar and reaction scalar, mapping the detailed chemical reaction process to the plane of these two scalar quantities. The numerical simulation results are in good agreement with the experimental data. The flame surface / reaction progress model can well simulate the turbulent diffusion flame and predict the flame instability. It is found that the probability of local flameout is larger at the cross section of the flame whose axial distance to the center jet diameter is 7.5 to 15, which is related to the large exponential dissipation rate of the scalar. The ratio of the flame axial distance to the center jet diameter is 30 After the flow field to re-ignite, because the mixture fraction and equivalence ratio becomes smaller, the flame more in lean state.