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通过大涡模拟得到三维等密度平面射流中的混合分数的动态演化过程并统计其概率密度(PDF)的分布,对非预混燃烧雷诺时均模拟中常用的简化模型,包括β函数和截尾高斯函数,进行了定性和定量分析。混合分数的PDF分布在流场的不同区域上定性存在较大的区别,可以分为四类:追随型单峰分布、非追随型单峰分布、平板型分布和双峰分布。单峰追随型主要分布在湍流充分发展区,对不同的简化模型都有较好的适应性;单峰非追随型PDF通过β函数模拟可以得到很好的结果;平板型分布PDF,定性上难以模拟但定量模拟效果好;双峰分布主要分布于湍流外问歇性较大的区域,现有简化PDF模型难以得到满意的结果。
Through the large eddy simulation, the dynamic evolution of the mixed fraction in a three-dimensional iso-density planar jet is obtained and its distribution of probability density (PDF) is calculated. The simplified model commonly used in the non-premixed combustion Reynolds average simulation, including the beta function and the truncated Gaussian function, qualitative and quantitative analysis. PDF distributions of mixed fraction have qualitatively different in different regions of flow field, which can be divided into four categories: follow-up unimodal distribution, non-follow-up unimodal distribution, plate type distribution and bimodal distribution. The monomodal follow-up is mainly distributed in a well-developed turbulence area and has good adaptability to different simplified models. Single-peak non-follow-up PDF can obtain good results through β-function simulation. The plate-type distribution PDF is qualitatively difficult Simulation but good quantitative simulation effect; bimodal distribution is mainly distributed in the turbulent interception of a larger area, the existing simplified PDF model is difficult to get satisfactory results.