Comparison of Presumed PDF Models of Turbulent Flames
Comparison of Presumed PDF Models of Turbulent Flames
复制标题
湍流火焰假定 PDF 模型的比较
DOI：
10.1155/2012/564621
复制
发表时间：
2012
影响因子：
0.7
通讯作者：
A. Lipatnikov
中科院分区：
文献类型：
--
作者：
Chen Huang;A. Lipatnikov
在过去的几年里，使用一个假定的概率密度函数（PDF）的燃烧过程变量或/和混合物分数已成为越来越流行的方法，平均反应速率在预混和部分预混湍流火焰。为此目的通常调用的是β函数PDF或狄拉克δ函数的组合，其中两个PDF的参数基于通过积分适当的平衡方程计算的它们的一阶矩和二阶矩的值来确定。由于就湍流燃烧的基本物理学而言，上述PDF的选择似乎是完全任意的，因此使用这种PDF意味着关键平均量对PDF形状的敏感性较弱。目前的工作是为了测试这个隐含的假设，通过比较平均热释放率，燃烧速度，等等，平均调用上述PDF，所有其他的东西都是相同的。在预混的情况下计算的结果表明，假定的燃烧过程变量PDF的形状的平均放热率的敏感性，从而，把问题的方法。相反，使用一个假定的混合分数PDF似乎是一个足够合理的简化建模的影响，在平均燃烧速度上的混合物分数的波动提供的混合物组成在可燃性范围内变化。
Over the past years, the use of a presumed probability density function (PDF) for combustion progress variable or/and mixture fraction has been becoming more and more popular approach to average reaction rates in premixed and partially premixed turbulent flames. Commonly invoked for this purpose is a beta-function PDF or a combination of Dirac delta functions, with the parameters of the two PDFs being determined based on the values of their first and second moments computed by integrating proper balance equations. Because the choice of any of the above PDFs appears to be totally arbitrary as far as underlying physics of turbulent combustion is concerned, the use of such PDFs implies weak sensitivity of the key averaged quantities to the PDF shape. The present work is aimed at testing this implicit assumption by comparing mean heat release rates, burning velocities, and so forth, averaged by invoking the aforementioned PDFs, with all other things being equal. Results calculated in the premixed case show substantial sensitivity of the mean heat release rate to the shape of presumed combustion-progress-variable PDF, thus, putting the approach into question. To the contrary, the use of a presumed mixture-fraction PDF appears to be a sufficiently reasonable simplification for modeling the influence of fluctuations in the mixture fraction on the mean burning velocity provided that the mixture composition varies within flammability limits.