Two-dimensional direct numerical simulation evaluation of the flame-surface density model for flames developing from an ignition kernel in lean methane/air mixtures under engine conditions
Two-dimensional direct numerical simulation evaluation of the flame-surface density model for flames developing from an ignition kernel in lean methane/air mixtures under engine conditions
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DOI：
10.1063/1.4757655
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发表时间：
2012-10-01
影响因子：
4.6
通讯作者：
Abraham, John
中科院分区：
文献类型：
--
作者：
Reddy, Harinath;Abraham, John
火焰表面密度（FSD）模型通常用于预混合湍流燃烧模拟，以提供大涡模拟和雷诺平均模拟的封闭性。在本研究中，通过直接数值模拟获得的数据，减少了化学成分，从稀甲烷-空气混合物的点火核中产生火焰，用于研究LES应用的FSD建模术语的准确性。本研究是在与稀燃天然气发动机相关的高温高压条件下进行的。研究了FSD输运方程中四项的闭包模型。观察到，由LES网格分解的传播项充分模拟了实际传播项，而无需额外的子网格尺度建模。另一方面，曲率项的闭合需要一个子网格比例模型。研究了两个亚网格尺度曲率模型，发现在点火核的早期演化过程中，实际曲率项与模型曲率项存在差异。随着发展中的火焰接近统计上的稳态，这种一致性得到改善。分析了子网格对流项的建模方法，发现在点火核的瞬态演化过程中，实际对流项与模型对流项的差异越来越大。应变速率项闭合的亚网格尺度模型在核生长的早期和后期都显示出不一致。一般来说，应变率和曲率模型对滤波器宽度的敏感性大于对流和传播模型。(C) 2012年美国物理研究所。[http://dx.doi.org/10.1063/1.4757655]
Flame surface density (FSD) models are often used in premixed turbulent combustion modeling to provide closure in large eddy simulations (LES) and Reynolds-averaged simulations. In the present study, data obtained from direct numerical simulation, with reduced chemistry, of flames developing from ignition kernels in lean methane-air mixtures is used to study the accuracy of the FSD modeling terms for LES applications. This study is conducted at elevated temperature and pressure conditions relevant to lean-burn natural gas engines. The closure models for four terms in the FSD transport equation are studied. It is observed that the propagation term as resolved by the LES grid adequately models the actual propagation term without additional sub-grid scale modeling. On the other hand, the closure of the curvature term requires a sub-grid scalemodel. Two sub-grid scale curvature models are studied and it is seen that there are differences between the actual and the modeled curvature terms during the early evolution of the ignition kernel. The agreement improves as the developing flame approaches a statistically steady-state. The modeling of the sub-grid convection term is analyzed and differences between the actual and the modeled terms are observed to grow during the transient evolution of the ignition kernel. A sub-grid scalemodel for the closure of the strain rate term shows disagreement at both early and late stages of kernel growth. In general, the sensitivity of the strain rate and curvature models to the filter width is found to be greater than for convection and propagation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4757655]