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A priori filtered chemical source term modeling for LES of high Karlovitz number premixed flames

机译：高Karlovitz数预混火焰LES的先验滤波化学源项建模。

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Assumptions behind closure models for the filtered source term are studied a priori using results from DNS of turbulent n-heptane/air premixed flames at varying Karlovitz numbers. Simulations with both detailed chemistry and tabulated chemistry, as well as unity and non-unity Lewis numbers, are used to determine if finite-rate chemistry and differential diffusion effects affect the filtered chemical source terms. While the unfiltered source term shows large fluctuations, the filtered source terms from detailed chemistry and tabulated chemistry are in good agreement at sufficiently large filter widths (Delta greater than or similar to I-F). Using the concept of optimal estimators, it is shown that a tabulation approach using the filtered progress variable and its variance can predict accurately the filtered chemical source terms. Finally, the filtered source terms from the DNS are compared to predictions from two commonly assumed sub-filter probability density function models. Both models show deviations from the filtered DNS source terms but predict accurately the mean turbulent flame speed. The results illustrate the potential of using simple tabulated chemistry approaches based on presumed PDFs for LES of premixed flames in the thin and distributed reaction zones regimes.(C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：使用来自不同庚烷数的正庚烷/空气预混火焰的DNS结果，先验研究了过滤源项的封闭模型背后的假设。具有详细化学和列表化学的模拟，以及统一和非统一的Lewis数，可用于确定有限速率化学和微分扩散效应是否影响过滤的化学源项。尽管未过滤的源项显示出较大的波动，但在足够大的过滤器宽度（Delta大于或类似于I-F）下，来自详细化学和列表化学的已过滤源项非常吻合。使用最佳估计量的概念，可以证明，使用经过过滤的进度变量及其方差的列表方法可以准确地预测经过过滤的化学源项。最后，将来自DNS的已过滤源项与来自两个通常假定的子过滤器概率密度函数模型的预测进行比较。两种模型都显示出与过滤的DNS源项的偏差，但可以准确预测平均湍流火焰速度。结果表明，在稀薄和分布反应区方案中，使用基于简单PDF的简单列表化学方法处理预混火焰LES的潜力。（C）2016 The Combustion Institute。由Elsevier Inc.出版。保留所有权利。

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