An a priori assessment of the disparities in estimating the filtered chemical reaction rates in Large-Eddy Simulations (LES) is performed using two Direct Numerical Simulations (DNS) of turbulent premixed flames. DNS of turbulent premixed flames with the same turbulent Reynolds number but different Karlovitz numbers are carried out using semi-detailed finite-rate chemistry to represent different flame conditions. The sensitivities of the differences between the LES-filtered chemical reaction rates and those constructed using LES-filtered thermochemical variables (referred to as ‘disparity’ below) to reaction types, species characteristics, and flame conditions are systematically investigated. The sensitivity to reaction type is examined by quantifying the disparity in the filtered temperature-dependent reaction rate constant as a function of kinetic rate parameters. The sensitivity to species characteristics is examined by quantifying the disparity in the filtered law of mass action as a function of species chemical time scales and formation location. The sensitivity to flame conditions is examined by contrasting the results obtained from the two simulations. These disparities are compared to characterise distinct reaction/species categories with different levels of disparity in estimating the filtered chemical reaction rates in LES. For both flames, it is found that the rate constants estimated using LES-filtered temperature severely under-predict the LES-filtered rate constants, especially for reactions with high activation energies. The law of mass action estimated using LES-filtered species concentrations severely over-predicts the LES-filtered law of mass action, especially for reactions involving reactants with small chemical time scales. The combined effects are found to lead to considerable differences between the LES-filtered chemical reaction rates and those constructed using LES-filtered thermochemical quantities for all reaction types involving different classes of reactants typically included in combustion reaction mechanisms. The details and explanations of these differences provide test cases useful to the improvement of key LES modelling approximations.

中文翻译：

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使用湍流预混火焰的 DNS 评估 LES 中过滤化学反应速率的差异

使用湍流预混火焰的两个直接数值模拟 (DNS) 对大涡模拟 (LES) 中估计过滤化学反应速率的差异进行了先验评估。具有相同湍流雷诺数但不同卡洛维茨数的湍流预混火焰的 DNS 使用半详细的有限速率化学来表示不同的火焰条件。系统地研究了 LES 过滤的化学反应速率和使用 LES 过滤的热化学变量构建的反应速率（以下称为“差异”）之间的差异对反应类型、物种特征和火焰条件的敏感性。通过量化过滤的温度相关反应速率常数作为动力学速率参数的函数的差异来检查对反应类型的敏感性。通过将过滤的质量作用定律的差异量化为物种化学时间尺度和地层位置的函数，来检查对物种特征的敏感性。通过对比从两个模拟中获得的结果来检查对火焰条件的敏感性。比较这些差异以表征在估计 LES 中过滤的化学反应速率时具有不同差异水平的不同反应/物种类别。对于两种火焰，发现使用 LES 过滤温度估计的速率常数严重低估了 LES 过滤的速率常数，尤其是对于具有高活化能的反应。使用 LES 过滤的物质浓度估计的质量作用定律严重高估了 LES 过滤的质量作用定律，特别是对于涉及具有小化学时间尺度的反应物的反应。发现综合效应导致 LES 过滤的化学反应速率与使用 LES 过滤的热化学量构建的反应速率之间存在显着差异，所有反应类型涉及燃烧反应机制中通常包含的不同类别的反应物。这些差异的细节和解释提供了有助于改进关键 LES 建模近似的测试用例。发现综合效应导致 LES 过滤的化学反应速率与使用 LES 过滤的热化学量构建的反应速率之间存在显着差异，所有反应类型涉及燃烧反应机制中通常包含的不同类别的反应物。这些差异的细节和解释提供了有助于改进关键 LES 建模近似的测试用例。发现综合效应导致 LES 过滤的化学反应速率与使用 LES 过滤的热化学量构建的反应速率之间存在显着差异，所有反应类型涉及燃烧反应机制中通常包含的不同类别的反应物。这些差异的细节和解释提供了有助于改进关键 LES 建模近似的测试用例。