Large eddy simulation of a lifted ethylene flame using a dynamic nonequilibrium model for subfilter scalar variance and dissipation rate
Large eddy simulation of a lifted ethylene flame using a dynamic nonequilibrium model for subfilter scalar variance and dissipation rate
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DOI：
10.1016/j.proci.2012.06.079
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发表时间：
2013
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影响因子：
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通讯作者：
C. Kaul;V. Raman;E. Knudsen;E. Richardson;Jacqueline H. Chen
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文献类型：
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作者：
C. Kaul;V. Raman;E. Knudsen;E. Richardson;Jacqueline H. Chen
使用大涡模拟（LES）的非预混湍流燃烧的准确预测，需要详细的模拟燃料和氧化剂之间的混合比LES过滤器分辨率更精细的尺度。在守恒标量燃烧模型中，小尺度混合过程由子滤波标量方差和子滤波标量耗散率两个参数来量化。这些数量最常用的模型假设方差的产生和耗散之间存在局部平衡。这样的假设在实际的、技术上相关的流动配置中具有有限的有效性。然而，非平衡模型的方差和耗散率通常包含一个模型系数，其最佳值是未知的先验给定的模拟。此外，传统的动态过程是没有用的估计该系数的值。在这项工作中，一个替代的动态过程的基础上的子滤波器标量方差的传输方程。这种动态非平衡建模方法用于模拟湍流提升乙烯火焰，Yoo等人（2011）先前使用DNS进行了研究。新模型的预测相比，静态非平衡建模方法使用假设的模型系数，以及那些平衡建模方法。平衡模型被发现系统underpredict两个子滤波器标量方差和耗散率。使用的动态过程中示出，以增加非平衡建模方法的准确性。然而，基于网格的隐式滤波的结果出现的数值误差似乎降低了所有三个建模选项的准确性。因此，虽然这些结果证实了新的动态模型的有用性，他们也表明，子滤波器模型预测的质量取决于几个外在的子滤波器模型本身的制定因素。
Accurate prediction of nonpremixed turbulent combustion using large eddy simulation (LES) requires detailed modeling of the mixing between fuel and oxidizer at scales finer than the LES filter resolution. In conserved scalar combustion models, the small scale mixing process is quantified by two parameters, the subfilter scalar variance and the subfilter scalar dissipation rate. The most commonly used models for these quantities assume a local equilibrium exists between production and dissipation of variance. Such an assumption has limited validity in realistic, technically relevant flow configurations. However, nonequilibrium models for variance and dissipation rate typically contain a model coefficient whose optimal value is unknown a priori for a given simulation. Furthermore, conventional dynamic procedures are not useful for estimating the value of this coefficient. In this work, an alternative dynamic procedure based on the transport equation for subfilter scalar variance is presented. This dynamic nonequilibrium modeling approach is used for simulation of a turbulent lifted ethylene flame, previously studied using DNS by Yoo et al. (2011). The predictions of the new model are compared to those of a static nonequilibrium modeling approach using an assumed model coefficient, as well as those of the equilibrium modeling approach. The equilibrium models are found to systematically underpredict both subfilter scalar variance and dissipation rate. Use of the dynamic procedure is shown to increase the accuracy of the nonequilibrium modeling approach. However, numerical errors that arise as a consequence of grid-based implicit filtering appear to degrade the accuracy of all three modeling options. Thus, while these results confirm the usefulness of the new dynamic model, they also show that the quality of subfilter model predictions depends on several factors extrinsic to the formulation of the subfilter model itself.