In this study, large eddy simulations (LES) are conducted using both a finite-rate chemistry (FRC) model and a flamelet/progress-variable (FPV) model for a series of piloted partially premixed methane/air flames of increasing turbulence intensity (Sandia Flames D, E, and F). From Flame D to E to F, as flow velocity and strain rate increase, the flame is either pushed downstream and extended radially or weakened by enhanced local extinction. The two combustion models produce different spatial distributions of both time-averaged quantities and instantaneous flame field. The FPV model provides an overall better prediction of the time-averaged axial and radial profiles of Flame D, but a significantly worse prediction of Flame F, primarily because the FPV model significantly over predicts local extinction. In terms of the conditional statistics, in which the effects of spatial distribution of mixture fraction and subgrid-scale (SGS) modeling are largely “removed,” the FRC model provides better predictions than the FPV model for all quantities at most locations and mixture fractions in all three flames. The effect of differential diffusion on the prediction of a species depends on the molecular diffusivity of that species; the effect is typically smaller than the difference between the FRC and FPV models.

在这项研究中，对于一系列湍流强度不断增加的先导式部分预混合甲烷/空气火焰，使用有限速率化学（FRC）模型和小火焰/进度可变（FPV）模型进行了大涡模拟（LES）（桑迪亚火焰D，E和F）。从火焰D到E到F，随着流速和应变率的增加，火焰被推向下游并径向延伸，或者由于局部消光增强而减弱。这两种燃烧模型会产生时间平均量和瞬时火焰场的不同空间分布。FPV模型对火焰D的时间平均轴向和径向轮廓提供了更好的整体预测，但对火焰F的预测却差得多，这主要是因为FPV模型大大预测了局部灭绝。就条件统计而言，在很大程度上“消除”了混合分数和亚网格规模（SGS）模型的空间分布的影响的情况下，对于三个位置的大部分位置和所有混合分数中的所有分数，FRC模型比FPV模型提供了更好的预测。差异扩散对物种预测的影响取决于该物种的分子扩散性。该效果通常小于FRC和FPV模型之间的差异。