湍流强旋流预混火焰大涡模拟研究

Large Eddy Simulation of Turbulent Strongly Swirling Premixed Flame

本文采用合成涡方法生成湍流进口条件,对非受限强旋流甲烷/空气贫燃预混火焰进行了大涡模拟研究。模拟结果和实验以及DNS数据符合良好。基于此模拟方法,本文对甲烷火焰掺混氢气和水蒸气,进行了比较研究。研究发现,掺混氢气提高了火焰抗拉伸灭火能力,火焰在外剪切层强湍流作用下形成较厚火焰刷。掺混水蒸气,火焰降温明显,流场轴向速度加速较小,形成较大的当地旋流数。因而,相比于掺混氢气,其回流区更强、更宽。相比于掺混水蒸气,流场轴向速度加速较大的掺氢火焰,其轴向脉动在更强的Kelvin-Helmholtz不稳定性作用下,下游剪切层双峰结构得到了保持并增强。

In this paper,the large eddy simulation(LES) studies on a unconfined strongly swirling CH4/air lean premixed flame were conducted.Using LES the calculation results are in excellent agreement with existing experimental and direct numerical simulation(DNS) results.Based on LES,we further investigated the effects of hydrogen and steam addition in lean premixed methane/air flames.The hydrogen addition increase the extinction limit induced by flame stretch.Therefore,the turbulent flame brush is thick.Compared with hydrogen addition,the effects of steam addition decrease the flame temperature.Moreover,the acceleration of streamwise velocity is not obvious and the local swirl number is smaller.Thus,the central recirculation is stronger and this recirculation zone is border.On the other hand,the hydrogen addition intensifies the flame and increases the streamwise velocity obviously.Therefore,due to the effects of Kelvin-Helmholtz instability,the double-peak shape in downstream shear layer can be maintained and enhanced.