中文摘要：

在不同射流速度条件下，对甲烷/空气预混射流火焰进行了大涡模拟.甲烷/空气预混射流气体按化学当量比混合，计算采用两步简化反应机理和WALE亚格子湍流输运模型，3个算例下流场特征和火焰结构计算结果与前人实验结果一致，中心线轴向速度和温度场结果与实验数据相符.通过对不同Karlovitz数条件下甲烷/空气预混射流火焰结构进行分析，并计算Takeno指数，研究了湍流涡对预混火焰的影响.研究发现：在Ka＜100(Ka＝37)条件下，预混射流火焰会出现预热区的增厚，放热区保持完整，湍流火焰保持为预混燃烧；在Ka＞100(Ka＝112)条件下，湍流火焰进入分布反应区模式.Takeno指数显示，由于卷吸和小尺度涡的作用，湍流火焰出现局部的部分预混燃烧.甲烷/空气预混射流湍流火焰的大涡模拟证实了湍流火焰分布反应区模式的特点：未燃气体与燃后气体之间不再有明显的界面，火焰面模型不再适用；反应区增厚，放热区展宽，放热率降低；由于卷吸和小尺度涡对火焰的作用，湍流火焰局部出现部分预混燃烧；湍流火焰温度降低，放热区附近温度场趋向均匀.

英文摘要：

Large-eddy simulation(LES)of premixed CH4/air jet flames at different jet velocity was investigated.The jetflames were stoichiometrically premixed.Two-step reduced scheme and WALE model were employed in the simulation.The structure of the premixed CH4/air jet flames is studied with different Karlovitz numbers(Ka=37,112).The interactionbetween flames and turbulent eddies was analyzed considering the Takeno index.The results show that:if Ka<100(Ka=37),the thickness of the preheat layer and thermal layer is distorted and thickened by turbulent eddies.Meanwhile,the reaction zone remains thin and intact;if Ka>100(Ka=112),the reaction zone of the premixed flame is broadenedby small eddies.The turbulent jet flame is evidenced to be within the distributed reaction zone regime.The Takenoindex indicates that partial premixed combustion occurs in some regimes.Compared with the flamelet regime,the distributedreaction zone regime has the following characteristics:the sharp interface between the fresh gas and the burnt productsis eliminated.Flamelet model is not available for simulations in this regime;the reaction zone and the heat releasezone are thickened,and the heat release rate is reduced;because of the entrainment and interaction with small eddies,partial premixed combustion occurs in some regions;the overall temperature of the turbulent flame is reduced and thetemperature field near the heat release zone tends to be more homogenized.