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混合分数概率密度函数(probability density function,PDF)反映了湍流对燃料和氧化剂混合过程的影响,在湍流非预混燃烧的理论研究和数值模拟中有非常重要的作用。该文基于大涡模拟(large eddy simulation,LES)对非预混火焰中的混合分数PDF进行了研究。利用LES预测的SandiaFlame D的速度和温度的均值和均方根分布与实验结果符合很好,瞬态温度场显示了合理的湍流火焰形态。混合分数PDF在反应区为钟形分布,在贫燃侧和富燃侧为钟形分布或单调形分布,取决于当地流场状态。对简化PDF模型的研究表明:β函数模型对钟形PDF和单调形PDF的预测效果都很好;截尾Gauss函数模型只能较好地预测钟形分布PDF;多点δ函数模型的预测能力与截尾Gauss函数模型的预测能力类似;双δ函数模型的预测结果偏差较大。
The mixed fraction probability density function (PDF) reflects the effect of turbulence on the mixing process of fuel and oxidizer. It plays a very important role in theoretical research and numerical simulation of turbulent non-premixed combustion. Based on large eddy simulation (LES), the mixed fractional PDF in non-premixed flame is studied. The mean and root mean square distributions of velocity and temperature of SandiaFlame D predicted by LES are in good agreement with the experimental results and the transient temperature field shows a reasonable turbulent flame morphology. The mixed fraction PDF has a bell-shaped distribution in the reaction zone and a bell-shaped or monotonous distribution on the lean and rich sides, depending on the local flow field conditions. The research on simplified PDF model shows that the β function model has a good predictive effect on bell-shaped PDF and monotone PDF; truncated Gauss function model can only predict the bell-shaped distribution PDF; the predictive ability of multi-point δ function model Which is similar to the predictive ability of truncated Gauss function model. The prediction results of double δ function model have large deviations.