A priori and a posteriori analyses of algebraic flame surface density modeling in the context of Large Eddy Simulation of turbulent premixed combustion
A priori and a posteriori analyses of algebraic flame surface density modeling in the context of Large Eddy Simulation of turbulent premixed combustion
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DOI：
10.1080/10407782.2016.1257309
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发表时间：
2017-01
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影响因子：
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通讯作者：
U. Allauddin;M. Klein;M. Pfitzner;N. Chakraborty
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文献类型：
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作者：
U. Allauddin;M. Klein;M. Pfitzner;N. Chakraborty
基于火焰表面密度（FSD）的反应速率闭合是大涡模拟（LES）中紊流预混火焰建模最重要的方法之一。favre过滤反应过程变量的输运方程需要封闭过滤反应速率和亚网格标量通量（SGSF）。预混合湍流火焰中的SGSF既有梯度分量，也有反梯度分量，其中前者通常使用涡动扩散系数来建模，后者可以单独建模，也可以使用适当的起皱因子与过滤后的反应速率项结合。目前的工作范围是结合已经建立的LES FSD模型，确定一个明确的SGSF闭包，以获得最佳性能。最近，作者利用一个直接数值模拟（DNS）数据库，在不同的湍流雷诺数范围内自由传播的湍流预混火焰，评估了不同的SGSF模型对预混湍流燃烧的性能。两个最有前途的模型已经在LES代码中实现了。基于先验DNS分析确定的建模方法，通过将湍流甲烷本生火焰的LES模拟结果与充分记录的实验数据进行比较，进一步进行后置评估。在不同的SGSF模型中没有观察到总体火焰速度的显著变化。然而，火焰的形状和厚度对SGSF的建模有响应。考虑到SGSF模型具有非常不同的特征，本工作中对LES结果的总体影响小于预期。对先前的先验DNS分析的扩展为观察到的行为提供了详细的解释。
ABSTRACT The flame surface density (FSD) based reaction rate closure is one of the most important methodologies of turbulent premixed flame modeling in the context of Large Eddy Simulations (LES). The transport equation for the Favre-filtered reaction progress variable needs closure of the filtered reaction rate and the subgrid scalar flux (SGSF). The SGSF in premixed turbulent flames has both gradient and countergradient components, where the former is typically modeled using eddy diffusivity and the latter can be modeled either on its own or in combination with the filtered reaction rate term using an appropriate wrinkling factor. The scope of the present work is to identify an explicit SGSF closure for the optimum performance in combination with an already established LES FSD model. The performance of different SGSF models for premixed turbulent combustion has been assessed recently by the authors using a Direct Numerical Simulation (DNS) database of freely propagating turbulent premixed flames with a range of different values of turbulent Reynolds number. The two most promising models have been implemented in the LES code. The modeling methodology identified based on a priori DNS analysis is assessed further a posteriori by comparing the LES simulation results of turbulent methane Bunsen flames with the well-documented experimental data. A significant change of the overall flame speed is not observed for different SGSF models. However, the flame shape and thickness respond to the modeling of SGSF. Considering the fact that the SGSF models have very different characteristics, the overall effect on the LES results in this work is smaller than expected. An extension of a previous a priori DNS analysis provides detailed explanations for the observed behavior.