A flamelet LES of turbulent dense spray flame using a detailed high-resolution VOF simulation of liquid fuel atomization
A flamelet LES of turbulent dense spray flame using a detailed high-resolution VOF simulation of liquid fuel atomization
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DOI：
10.1016/j.combustflame.2021.111742
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发表时间：
2021-09
影响因子：
4.4
通讯作者：
Jian Wen;Yong Hu;T. Nishiie;J. Iino;A. Masri;R. Kurose
中科院分区：
文献类型：
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作者：
Jian Wen;Yong Hu;T. Nishiie;J. Iino;A. Masri;R. Kurose
提出了一种用于模拟密集喷雾火焰的数值框架。在此框架下，通过详细的高分辨率VOF模拟求解了液体燃料（丙酮）的雾化，并将液滴的欧拉分量转换为拉格朗日液滴，存储在下游某个截面的数据库中。然后，燃烧过程由LES/FPV（火焰面进展变量）求解，该LES/FPV采用预先存储的拉格朗日液滴数据库（即，每个液滴的位置、尺寸和速度）作为入口边界条件。该框架是VOF模拟和燃烧模拟之间的单向耦合。通过与悉尼试验针式喷雾燃烧器的实验比较，研究了这种方法的有效性。VOF模拟表明，喷嘴出口处液滴的体积流量在时间和空间上都有波动，较大的液滴相对于较小的液滴更倾向于远离中心轴。计算的破碎长度与经验公式吻合较好。在喷雾火焰LES/FPV的拉格朗日液滴数据库中，采样截面的位置、采样时间以及E-L变换的阈值对液滴的性质有很大影响，是LES/FPV能否成功应用的关键。两个不同的凹进距离的喷雾火焰计算使用其最佳的预存储的液滴数据库，都显示出良好的协议与实验的气体温度和液滴尺寸分布。具有较长的凹进距离的喷雾火焰，这是更典型的稀喷雾，被认为是具有更长和更宽的预混核心比具有较短的凹进距离代表密集的喷雾。更密集的喷雾火焰的预测中的差异变得更加明显，导致进一步下游的气体温度的过度预测。文本中讨论了这种行为的原因。
A numerical framework used to model dense spray flames is proposed. In this framework, the liquid fuel (acetone) atomization is solved by a detailed high-resolution VOF simulation, and the Eulerian components of liquid droplets are transformed into Lagrangian droplets, which are stored in a database at a certain downstream cross-section. Then, the combustion process is solved by a LES/FPV (flamelet progress variable) adopting the pre-stored database of Lagrangian droplets (i.e., the position, size, and velocity of each droplet) as the inlet boundary conditions. This framework is a one-way coupling between a VOF simulation and a combustion simulation. The validity of this approach is investigated by comparing the computations with the experiments of the Sydney Piloted Needle Spray Burner. The VOF simulation shows that the volume flux of the droplets at the nozzle exit fluctuates both temporally and spatially and the larger droplets tend to be located away from the center axis compared to the small droplets. The computed breakup length is in good agreement with the empirical correlation. In the database of the Lagrangian droplets for the LES/FPV of spray flames, the location of the sampling cross-section, the sampling time, and the threshold value for Eulerian–Lagrangian (E-L) transformation strongly affect the properties of the Lagrangian droplets, and are critical for the successful use of the LES/FPV. Two spray flames with different recess distances are computed using their optimal pre-stored droplets databases and both show generally good agreement with the experiments in terms of the gas temperature and droplet size distributions. The spray flame with a longer recess distance, which is more representative of a dilute spray, is considered to have a longer and wider premixed core than that with a shorter recess distance representing a dense spray. The discrepancy in the prediction of denser spray flames becomes more evident leading to over-predictions of gas temperature further downstream. Reasons for this behavior are discussed in the text.