On the statistics of flame stretch in turbulent premixed jet flames in the thin reaction zone regime at varying Reynolds number
On the statistics of flame stretch in turbulent premixed jet flames in the thin reaction zone regime at varying Reynolds number
复制标题
DOI：
10.1016/j.proci.2018.06.194
复制
发表时间：
2019
影响因子：
3.4
通讯作者：
S. Luca;A. Attili;E. Lo Schiavo;F. Creta;F. Bisetti
中科院分区：
文献类型：
--
作者：
S. Luca;A. Attili;E. Lo Schiavo;F. Creta;F. Bisetti
直接数值模拟（DNS）用于研究湍流射流预混火焰中火焰表面拉伸的统计数据。重点放在表面产生和破坏的速率及其与雷诺数的关系上。根据总体速度、槽宽度和反应物的性质，在不断增加的雷诺数和高达 Re≈22×103 的条件下模拟了四种贫甲烷/空气湍流槽喷射火焰。卡洛维茨数保持大致恒定，火焰落在薄反应区区域。该模拟具有有限速率化学和混合物平均传输的特点。我们的数据表明，火焰表面面积增加到对应于平均火焰长度的 80% 的流向位置，然后随着表面破坏超过生产而减少。据观察，应变的切向速率平均是造成火焰表面的原因，而表面破坏是由于曲率项造成的。此外，我们发现这两项都显着大于它们的差值，即净表面拉伸。切向应变率的统计与均匀各向同性湍流中无穷小材料表面的统计非常吻合。一旦按照柯尔莫哥洛夫时间尺度进行缩放，两种拉伸贡献的平均值在很大程度上与位置无关，并且在具有不同雷诺数值的火焰中相等。表面破坏主要是由于传播到反应物中，其中表面折叠成圆柱形，曲率中心位于反应物一侧。反应表面的位移速度和曲率的联合统计有细微差别，最有可能出现的是平坦表面的负位移速度，而表面平均位移速度如预期为正。
Direct Numerical Simulations (DNS) are conducted to study the statistics of flame surface stretch in turbulent jet premixed flames. Emphasis is placed on the rates of surface production and destruction and their scaling with the Reynolds number. Four lean methane/air turbulent slot jet flames are simulated at increasing Reynolds number and up to Re ≈ 22 × 103, based on the bulk velocity, slot width, and the reactants’ properties. The Karlovitz number is held approximately constant and the flames fall in the thin reaction zone regime. The simulations feature finite rate chemistry and mixture-average transport. Our data indicate that the area of the flame surface increases up to the streamwise position corresponding to 80% of the average flame length and decreases afterwards as surface destruction overtakes production. It is observed that the tangential rate of strain is responsible for the production of flame surface in the mean and surface destruction is due to the curvature term. In addition, it is found that these two terms are both significantly larger than their difference, i.e., the net surface stretch.The statistics of the tangential strain rate are in good agreement with those for infinitesimal material surfaces in homogeneous isotropic turbulence. Once scaled by the Kolmogorov time scale, the means of both contributions to stretch are largely independent of location and equal across flames with different values of the Reynolds number. Surface destruction is due mostly to propagation into the reactants where the surface is folded into a cylindrical shape with the center of curvature on the side of the reactants. The joint statistics of the displacement speed and curvature of the reactive surface are nuanced, with the most probable occurrence being that of a negative displacement speed of a flat surface, while the surface averaged displacement speed is positive as expected.