Abstract In order to study the mixing mechanism of fuel and air in gas turbine, large eddy simulation has been used to investigate the methane jet-in-crossflow with the velocity ratio (R) of 1.5 and 4. This study aims to explore the formation mechanism of vortices such as the hairpin vortices, hovering vortices and horseshoe vortices, the relationship between the fuel–air mixing and flow characteristics at different velocity ratios. The numerical methods in the present work are firstly validated with the experimental data in terms of mean and root mean square values of velocity. For R = 4, the shear layer vortices, horseshoe vortices, counter-rotating vortices pairs (CVP) and wake vortices can be observed, while the jet shear layer cannot be observed for R = 1.5. The hairpin vortices originating from the vortice-ring are lifted and shed from the downstream of the jet-outlet due to Kutta-Joukowski lift. The hairpin vortices are similar to CVP. The horseshoe vortices in R = 1.5 and 4 are formed due to the blockage of the jet (CH4) and the crossflow (air) respectively, and its evolution is associated with the hovering vortices which only exist for R = 1.5. The uniform index and pr-obability density function are used for quantitative analysis of the mixing performance. The uniform index at X/D = 0 (fuel-inlet) and at X/D = 25 (outlet) are 0.033 and 0.335 for R = 1.5 and 0.130 and 0.047 for R = 4. For R = 4, the jet penetration is higher and the deflection angle of jet is smaller than that in case of R = 1.5. Higher R will provide more region for mixing, therefore uniform index is higher and the mixing is more uniform in the downstream.

中文翻译：

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基于LES的不同速度比横流射流湍流燃料空气混合研究

摘要 为了研究燃气轮机中燃料和空气的混合机理，采用大涡模拟研究了速度比（R）为1.5和4的甲烷横流射流。发夹涡、盘旋涡和马蹄涡等涡的形成机理，不同速度比下的燃料-空气混合与流动特性之间的关系。目前工作中的数值方法首先用实验数据在速度的均值和均方根值方面得到验证。当 R = 4 时，可以观察到剪切层涡、马蹄形涡、反向旋转涡对 (CVP) 和尾流涡，而当 R = 1.5 时无法观察到喷射剪切层。由于 Kutta-Joukowski 升力，源自涡环的发夹涡从喷气出口下游上升和脱落。发夹涡流类似于 CVP。R=1.5和4的马蹄形涡分别是由于射流（CH4）和横流（空气）的阻塞而形成的，其演化与仅存在于R=1.5的盘旋涡有关。均匀指数和概率密度函数用于混合性能的定量分析。X/D = 0（燃料入口）和 X/D = 25（出口）的均匀指数对于 R = 1.5 为 0.033 和 0.335，对于 R = 4 为 0.130 和 0.047。对于 R = 4，射流穿透为射流偏转角比 R = 1.5 的情况下更高，射流偏转角更小。更高的 R 将提供更多的混合区域，