Modeling of Turbulent Nonpremixed Combustion Using a Combined Probability Density Function/Moment Method

为了提高蒙特-卡罗方法的精度，提出了一种概率密度函数（PDF）/矩量法的组合方法。蒙特-卡罗方法的计算精度强烈依赖于蒙特-卡罗粒子的数目，并随着概率密度函数输运几率的减小而降低。本方法同时解决了一个模型化的PDF传输方程和矩方程的均值和方差。从矩方程中得到的均值和方差值仅作为参考值与PDF的相应值进行匹配。本方法的有用性进行了评估的湍流射流扩散火焰的配置，与其他方法的比较; PDF方法和火焰面模型方法。为了获得组合方法的基准数据，我们调查了圆柱形炉膛中的射流非预混火焰的排放特性和提升射流非预混火焰的火焰底部结构的统计。重新 ...更多信息 结果表明：（1）本文提出的PDF/矩量法与火焰面模型法的比较，验证了PDF法的优越性。结合PDF/矩方法可以再现射流非预混火焰的熄灭和再点燃过程。2）受限火焰的火焰特性受燃烧器和炉膛几何结构的影响。在本研究中，圆筒形炉的内径，在火焰边界处的湍流，和全球当量比的影响进行了检查的NOx的排放。结果表明，NOx排放指数随这些参数的增加而减小。3）采用平面温度瑞利散射方法，对非预混火焰底部的非预混小火焰统计特性进行了实验研究。标量耗散率具有对数正态统计特性，猝灭标量耗散率低于使用均匀应变对流非预混火焰预测的临界值。少

A combined probability density function (PDF)/moment method has been developed to improve the accuracy of the Monte-Carlo method. The accuracy of Monte-Carlo method depends strongly on the number of Monte-Carlo particles and declines with the decrease in the PDF transport probability. The present method solves simultaneously a modeled PDF transport equation and moment equations of mean and variance. Both the mean and variance values obtained from the moment equations are just used as the reference values to match to the corresponding values of PDFs. The usefulness of the present method is evaluated in the configuration of a turbulent jet diffusion flame, with a comparison with other methods; the PDF method and the flamelet model method. In order to obtain the benchmark data of the combined method, we investigated the emission characteristics of jet nonpremixed flames confined in cylindrical furnaces and the statistics of the flame base structure of lifted jet nonpremixed flames. The re … More sults obtained are as follows.1) The comparison between the present combined PDF/moment method and the flamelet model method have verified the improvement from the PDF method. The combined PDF/moment method can reproduce the extinction and the re-ignition in jet nonpremixed flames.2) The flame characteristics of confined flames can be strongly dominated by the combination of the burner and furnace geometries. In the present study, the effects of the inner diameter of the cylindrical furnace, the turbulence at the flame boundary, and the global equivalence ratio are examined in terms of the emission of NOx. It was found that the emission index of NOx decreases roughly with these parameters.3) Nonpremixed flamelet statistics at the flame base of lifted turbulent nonpremixed flames were investigated experimentally using a planer temperature Rayleigh scattering method. The scalar dissipation rate has log-normal statistics and the quenching scalar dissipation rate is lower than the critical value predicted using the uniformly strained counter nonpremixed flame. Less