当前位置: X-MOL 学术Combust. Sci. Technol. › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
Flame Surface Density Transport Statistics for High Pressure Turbulent Premixed Bunsen Flames in the Context of Large Eddy Simulation
Combustion Science and Technology ( IF 1.9 ) Pub Date : 2020-07-13 , DOI: 10.1080/00102202.2020.1789122
Felix B. Keil 1 , Nilanjan Chakraborty 2 , Markus Klein 1
Affiliation  

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.



中文翻译:

大涡模拟背景下高压湍流预混本生火焰的火焰表面密度输运统计

在大涡模拟的背景下,分析了高压对火焰表面密度(FSD)输运统计的统计行为以及FSD输运方程未封闭项的选定已建立子模型的行为的影响。为此,已经从现有数据库中考虑了五个湍流预混本生火焰。四个本生火焰的特征在于不同的压力水平,并且位于起皱和波纹小火焰(CF)方案的边界上,以便可能并清楚地识别经常在高压下观察到的燃烧不稳定性。第五个火焰处于稀薄的反应区状态,并作为比较的参考案例。对于给定的过滤器宽度与火焰厚度比,对于不同的压力水平,FSD输运方程及其模型的项在质上相似。但是,随着火焰厚度随着压力的增加而减小,对于由火焰厚度归一化为与大气火焰相同的空间分辨率(即LES过滤器宽度)的高压火焰不太可能被模拟。空间分辨率很可能保持恒定,在这种情况下,对于较高的压力,建模变得更具挑战性:对于较大的过滤器宽度与火焰厚度之比,子网格贡献的大小会增加,从而子网格的精度也会提高建模有望在确定仿真的保真度方面发挥更重要的作用。在这项工作中考虑的火焰的特征在于湍流速度波动与层流火焰速度的比率相对较低,在这些条件下,朝着网格的前沿观察到子网格曲率项的正值和应变率项的负值。火焰刷。完善的子网格曲率项现有模型无法捕获此行为,因为这些模型表达式确定性地产生负值。类似地,切向应变项的现有模型确定性地产生正值。对于FSD输运方程的未封闭项的观察行为及其各自的模型预测,已提供了详细的说明。朝着火焰刷的前边缘观察到子网格曲率项的正值和应变率项的负值。完善的子网格曲率项现有模型无法捕获此行为,因为这些模型表达式确定性地产生负值。类似地,切向应变项的现有模型确定性地产生正值。对于FSD输运方程的未封闭项的观测行为及其各自的模型预测,已提供了详细的说明。朝着火焰刷的前边缘观察到子网格曲率项的正值和应变率项的负值。完善的子网格曲率项现有模型无法捕获此行为,因为这些模型表达式确定性地产生负值。类似地,切向应变项的现有模型确定性地产生正值。对于FSD输运方程的未封闭项的观测行为及其各自的模型预测,已提供了详细的说明。现有的切向应变项模型可确定地产生正值。对于FSD输运方程的未封闭项的观测行为及其各自的模型预测,已提供了详细的说明。现有的切向应变项模型可确定地产生正值。对于FSD输运方程的未封闭项的观测行为及其各自的模型预测,已提供了详细的说明。

更新日期:2020-07-13
down
wechat
bug