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首页> 外文期刊>Combustion and Flame >Prediction of extinction and reignition in nonpremixed turbulent flames using a flamelet/progress variable model 2. Application in LES of Sandia flames D and E
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Prediction of extinction and reignition in nonpremixed turbulent flames using a flamelet/progress variable model 2. Application in LES of Sandia flames D and E

机译：使用小火焰/进行变量模型预测非预混湍流火焰的熄灭和着火。2. Sandia火焰D和E在LES中的应用

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摘要

An extension of the flamelet/progress variable (FPV) model for the prediction of extinction and reignition is applied in large-eddy simulation (LES) of (lames D and E of the Sandia piloted turbulent jet flame series. This model employs a presumed probability density function (PDF), in which the marginal PDF of a reactive scalar is modeled by a statistically most likely distribution. This provides two advantages. First of all, the shape of the distribution depends on chemical and mixing time-scale information, and second, an arbitrary number of moments can be enforced. This model was analyzed in an a priori study in the first part of this work. In the present LES application, the first two moments of mixture fraction and reaction progress variable are used to constrain the shape of the presumed PDF. Transport equations for these quantities are solved, and models for the residual scalar dissipation rates, which appear as unclosed terms in the equations for the scalar variances, are provided. Statistical flow field quantities for axial velocity, mixture fraction, and temperature, obtained from the extended FPV model, are in good agreement with experimental data. Mixture-fraction-conditioned data, conditional PDFs, and burning indices are computed and compared with the delta-function flamelet closure model, which employs a Dirac distribution as a model for the marginal PDF of the reaction progress parameter. The latter model considerably underpredicts the amount of local extinction, which shows that the consideration of second-moment information in the presumed PDF of the reaction progress parameter is important for the accurate prediction of extinction and reignition. Mixture-fraction-conditioned results obtained from the extended FPV model are in good agreement with experimental data; however, the overprediction of the consumption of fuel and oxidizer on the fuel-rich side results in an overprediction of minor species. The predictions for the conditional PDFs and burning indices arc in good agreement with measurements.
机译：用于预测灭绝和着火的小火焰/进展变量（FPV）模型的扩展被用于大涡模拟（LES）的桑迪亚操纵湍流射流火焰序列的层D和E。密度函数（PDF），其中反应性标量的边际PDF通过统计上最可能的分布来建模，这提供了两个优点：首先，分布的形状取决于化学和混合时间尺度信息，其次，可以强制执行任意数量的矩，在本工作的第一部分中，对模型进行了先验分析，在当前的LES应用中，使用了混合分数和反应进度变量的前两个矩来约束形状解决了这些量的输运方程，并提供了剩余标量耗散率的模型，这些模型在标量方差方程中以未封闭的术语出现。 ded。从扩展的FPV模型获得的轴向速度，混合比和温度的统计流场数量与实验数据非常吻合。计算混合物分数条件数据，条件PDF和燃烧指数，并将其与δ函数小火焰闭合模型进行比较，该模型采用狄拉克分布作为反应进度参数的边际PDF模型。后一种模型大大低估了局部灭绝的数量，这表明在反应进程参数的假定PDF中考虑第二时刻信息对于准确预测灭绝和复燃非常重要。从扩展的FPV模型获得的混合分数条件结果与实验数据吻合良好。但是，对燃料和氧化剂消耗量过高的预测在燃料丰富的一侧导致了对次要物种的过高预测。条件PDF和燃烧指数的预测与测量结果非常吻合。

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