Application of PDF mixing models to premixed flames with differential diffusion
Application of PDF mixing models to premixed flames with differential diffusion
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DOI：
10.1016/j.combustflame.2012.02.026
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发表时间：
2012-07
影响因子：
4.4
通讯作者：
E. Richardson;Jacqueline H. Chen
中科院分区：
文献类型：
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作者：
E. Richardson;Jacqueline H. Chen
差速扩散改变了湍流预混燃烧中反应和扩散的平衡，影响燃烧装置的性能和排放。使用概率或过滤密度函数（PDF 或 FDF）方法对燃烧装置进行建模可以精确处理化学反应引起的成分变化，同时必须对分子混合进行建模。以前的 PDF 分子混合模型并未以满足可实现性要求的方式考虑差异扩散。针对一般的成对交换混合模型，提出了一种处理差分扩散的新方法，确保了可实现性，并应用于 Dopazo 的平均交换交互（IEM）模型 [26]，以及 Subramaniam 和 Pope 的欧几里得最小生成树（EMST）模型 [5]。新的微分扩散模型分别称为 IEM-DD 和 EMST-DD。湍流预混合甲烷-空气燃烧的二维和三维 DNS 结果表明，混合速率和物质质量分数的条件统计取决于物质扩散率和燃烧状态。针对二维 DNS 情况获得的零维 PDF 模型结果表明，EMST-DD 模型最好地再现了 DNS 中差异扩散的特征。 EMST-DD 模型的基本特征是在成分空间中局部混合的模型中施加了不同的混合率，这也是其在湍流预混燃烧中取得成功的原因。
Differential diffusion alters the balance of reaction and diffusion in turbulent premixed combustion, affecting the performance and emissions of combustion devices. Modelling combustion devices with Probability or Filtered Density Function (PDF or FDF) methods provides an exact treatment for the change in composition due to chemical reaction, while molecular mixing has to be modelled. Previous PDF molecular mixing models do not account for differential diffusion in a manner which satisfies realizability requirements. A new approach for treating differential diffusion, which ensures realizability, is proposed for pairwise-exchange mixing models in general, and applied in the Interaction by Exchange with the Mean (IEM) model of Dopazo [26], and in the Euclidean Minimum Spanning Tree (EMST) model of Subramaniam and Pope [5]. The new differential diffusion models are referred to as IEM-DD and EMST-DD respectively. Results from two and three-dimensional DNS of turbulent premixed methane–air combustion show that mixing rates and conditional statistics of species mass fractions depend on species diffusivities and the combustion regime. Zero-dimensional PDF model results obtained for the two-dimensional DNS case show that the EMST-DD model best reproduces the features that characterize differential diffusion in the DNS. The essential feature of the EMST-DD model, which accounts for its success in turbulent premixed combustion, is that differential mixing rates are imposed within a model which mixes locally in composition space.