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首页> 外文期刊>Combustion Science and Technology >Flame Surface Density Transport Statistics for High Pressure Turbulent Premixed Bunsen Flames in the Context of Large Eddy Simulation
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Flame Surface Density Transport Statistics for High Pressure Turbulent Premixed Bunsen Flames in the Context of Large Eddy Simulation

机译：大型涡仿真背景下高压湍流预混包森火焰的火焰表面密度传输统计

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摘要

The implications of elevated pressure on the statistical behavior of the flame surface density (FSD) transport statistics together with the behavior of selected established sub-models of the unclosed terms of the FSD transport equation have been analyzed in the context of large eddy simulation. For this purpose, five turbulent premixed Bunsen flames have been considered from an existing database. Four of the Bunsen flames are characterized by different pressure levels and are located on the boundary of the wrinkled and the corrugated flamelet (CF) regimes to allow for the possibility and clear identification of combustion instabilities that are often observed at high pressures. The fifth flame is in the thin reaction zones regime and serves as a reference case for the purpose of comparison. For a given filter width to flame thickness ratio, the terms of the FSD transport equation and their models behave in a qualitatively similar manner for different pressure levels. However, as the flame thickness decreases with increasing pressure, it is unlikely that a high pressure flame will be simulated for the same spatial resolution (i.e. LES filter width) normalized by flame thickness as that of an atmospheric flame. It is more likely that the spatial resolution remains constant and in this case, the modeling becomes much more challenging for higher pressures: the magnitudes of the sub-grid contributions increase for larger filter width to flame thickness ratio and thus the accuracy of sub-grid modeling is expected to play a more important role in determining the fidelity of the simulations. The flames considered in this work feature a relatively low ratio of turbulent velocity fluctuations to laminar flame speed, and under these conditions, positive values of the sub-grid curvature term and negative values of the strain rate term are observed toward the leading edge of the flame brush. This behavior cannot be captured by the well-established existing models for the sub-grid curvature term as these model expressions yield deterministically negative values. Similarly, existing models for the tangential strain term yield deterministically positive values. Detailed explanations have been provided for the observed behaviors of the unclosed terms of the FSD transport equations and their respective model predictions.
机译：在大涡模拟的背景下，已经分析了在大涡模拟的背景下分析了对火焰表面密度（FSD）传输统计的统计行为对FSD传输方程的所选择的子模型的行为的升压。为此目的，已从现有数据库中考虑了五个湍流预混的Bunsen火焰。四个Bunsen火焰的特征在于不同的压力水平，并且位于皱纹和波纹阵列（CF）方面的边界上，以允许在高压下经常观察到的燃烧稳定性的可能性和清晰的识别。第五火焰处于薄的反应区状态，并用作比较目的的参考案例。对于给定的滤波器宽度，对火焰厚度比，FSD传输方程的术语及其模型以与不同的压力水平的定性类似的方式行事。然而，随着火焰厚度随着压力的增加而减小，由于火焰厚度的相同空间分辨率（即LES滤光宽度），将模拟高压火焰不太可能是由火焰厚度归一化的。空间分辨率更可能仍然是恒定的，在这种情况下，对更高压力的建模变得更具挑战性：子电网贡献的大小增加，较大的滤波器宽度增加到火焰厚度比，从而增加了子网格的精度预计建模将在确定模拟的保真度方面发挥更重要的作用。在该工作中考虑的火焰具有相对较低的湍流速度波动与层流火焰速度的比率，并且在这些条件下，朝向前缘观察到应变速率术语的子网格曲率术语和负值的正值火焰刷。由于这些模型表达式产生的确定性负值，因此无法通过良好的现有模式捕获此行为。类似地，现有模型对于切向应变术语产量的确定性正值。已经为FSD传输方程的未缩减条款及其各自的模型预测的观察到的观察行为提供了详细说明。

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