双旋流火焰不稳定性模态转换

Flame Instability Modal Conversion of Double-Swirl Flame

采用DTF燃烧模型通过大涡模拟(LES)对本课题组设计的燃烧室中甲烷/空气贫燃预混旋流火焰的燃烧不稳定性模态转换现象进行了研究.通过计算不同当量比的燃烧状况,在当量比渐增到0.9附近时,发现火焰结构出现明显变化,火焰模态从M型转换为V型.对此过程计算的数据进行后处理,分析其前后各自温度场,平均轴向、径向燃烧室内速度分布,取x分别为5 mm、15 mm、25 mm、40 mm、60 mm处轴向和径向脉动速度,采用Q准则方法,POD方法分析流场中的涡旋结构,从而分析其燃烧不稳定性和影响火焰结构的主要因素.发现模态转换前平均火焰为“M”型,转换后为“V”型,V型火焰是一种更为稳定的火焰结构,火焰模态的转换受内、外剪切层位置的直接影响并与涡脱落模式有重要关系.

The modal conversion of combustion instability in a combustion chamber with methane-air lean premixed swirl flame was studied by using a DTF combustion model through large eddy simulation(LES).By calculating the combustion conditions under different equivalent ratios,it is found that when the equivalent ratio gradually increases to around 0.9,there is an obvious modal conversion in the combustion from M-type flame modal to V-type flame modal.Through post-processing the data calculated in this process,the temperature field before and after the modal conversion is analyzed,and the average axial and radial velocity distributions of the combustion chamber are obtained.The axial and radial pulsation speeds at x=5mm,15 mm,25 mm,40 mm,60 mm are taken,and the Q criterion and POD method are adopted to analyze the flow field in the vortex structure,so as to analyze the combustion instability and the main factors influencing the flame structure.It is found that the average flame is of"M"type before modal conversion and of"V"type after modal conversion.The V-type flame is a more stable flame structure.Flame modal conversion is directly affected by the position of inner and outer shear layers and has an important relationship with vortex shedding mode.