湍流扩散火焰局部熄火现象的大涡模拟研究

Large Eddy Simulation of Local Extinction of Turbulent

关键词:  湍流扩散火焰  大涡模拟  火焰面/反应进度模型  局部熄火

Key words:  Turbulent non-premixed flame  Large eddy simulation  Flamelet/progress variable model  Local extinction

摘要:

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。

Abstract:

Large eddy simulation (LES) of the Sandia turbulent jet flame E with the flamelet/progress variable model was applied to investigate characteristics of the turbulent non-premixed flames and analyse the mechanisms of local extinction. The flamelet/progress variable model is a model based on a conserved scalar and a reaction progress variable. Detailed chemical reaction process will be mapped into the plane of the two characteristic scalars. The numerical results are in good agreement with the experimental data，which indicates that the flamelet/progress variable model can well predict the combustion instabilities of turbulent non-premixed flames. It is found that the probability of local extinction is relatively large at the region where the ratio of axial distance over jet diameter is from 7.5 to 15，owning to high scalar dissipation rate there. In the downstream of this ratio being 30，the re-ignition occurs due to the low mixture fraction and small equivalence ratio，and lean combustion state dominates the whole fields.