燃料分级对旋流火焰的动态特性影响研究

Effects of Fuel Stage on Dynamic Characteristics of Swirling Flame

关键词:  分级旋流火焰  剪切层  回火  大涡模拟  进动涡核

Key words:  Stratified swirl flame  Shear layer  Flashback  Large eddy simulation  Precessing vortex core

摘要:

为深入研究分级旋流火焰特性，以分级旋流模型燃烧室为研究对象，对四个不同燃料分级比(R_f)条件下的分级旋流火焰进行了数值研究，在时均燃烧场特性分析的基础上进一步对燃料分级比为1和3两个工况进行了基于壁面建模的大涡模拟(WMLES)研究。结果表明：燃料分级比的改变会影响中心回流区(CRZ)的长度和宽度。燃烧室中截面的散点分布图能够显示出不同燃料分级比条件下的燃烧特征。燃料分级比为1时，燃烧室剪切层仅存在零散的涡破碎区；而燃料分级比为3时，伴随涡破碎区还出现了单螺旋分支进动涡核(PVC)。通过FFT变换获得的燃烧室内剪切层速度能谱主频与进动涡核的旋转频率相同，表明内剪切层速度脉动的产生与进动涡核有关。另外进动涡核会使流场内的燃料分布和燃烧模式发生周期性的变化，进而影响燃烧过程。调整燃料分级比在1附近，能够使分级火焰达到稳定燃烧降低排放的目标。

Abstract:

In order to deeply study the characteristics of the stratified swirl flame, the staged swirl model combustor was taken as a research object. The stratified swirl flame in four different fuel stratification ratios (R_f) was studied by numerical simulation method. Based on the time-averaged combustion field of R_f=1， 3, a large eddy simulation (LES) study was conducted. The results show that the change of the R_f will affect the length and width of the central recirculation zone (CRZ). The scatter plot of the combustor cross section shows different features in different R_fs. When the R_f=1, there are only scattered vortex breaking zones in the shear layer. When the R_f=3, there is a single spiral branch precessing vortex core (PVC) appeared along with the vortex breaking zone. The velocity energy spectrum dominant frequency of the point in the inner shear layer obtained by FFT transformation is the same as the rotation frequency of the PVC. This results indicate that the generation of velocity pulsation in the inner shear layer is related to the PVC. In addition, the PVC causes periodic change of the fuel distribution and combustion mode in the combustion flow field, which affect the combustion process. Adjusting the R_f around 1 can achieve the goal of stabilizing combustion and reducing emissions.