同心旋流分层预混火焰的动力学模态分析

Dynamic Mode Analysis on Internally-Staged-Swirling Stratified Premixed Flame

关键词:  航空发动机  低排放燃烧室  同心旋流分层预混火焰  动力学模态分解  燃烧不稳定性

摘要:

为了探究同心旋流分层火焰的不稳定燃烧问题，需要对火焰的动态脉动特性进行分析。采用高速摄像捕捉了自激和外激条件下同心旋流分层预混火焰的CH*化学发光动态图像，利用动力学模态分解（DMD）方法研究其主导脉动模态，提取出了相关模态的空间形态和脉动幅值，证明燃烧组织方式的改变会对火焰脉动的形态和规律产生影响。研究发现：模态分解可以反映分层旋流火焰的动态响应特征，并能解析脉动空间结构，验证火焰形态和外激频率对火焰动态响应的影响，其规律和火焰传递函数结果符合，且在分层比0.5~2内提高分层比使释热中心转移到预燃级和主燃级的剪切层内，300Hz~400Hz释热脉动将加强。验证了DMD方法适用于处理分析复杂分层旋流火焰的脉动特征，可为燃烧振荡控制提供参考。

Abstract:

In order to explore the issues of combustion instabilities in the internally-staged-swirling stratified flame, analysis on the characteristics of dynamic flame fluctuations are required. The high-speed camera with CH* filter are used to seize the dynamic images of this kind of flame under self-excited and forced-excited conditions. After that, DMD (Dynamic Mode Decomposition) method are adopted to analyze the dominant modes of fluctuation, seizing its spatial structure and amplitudes. By that means, it is proved that the combustion organization would affect the shapes and patterns of fluctuations. The dynamic response characteristics of swirling flame could be reflected from the mode analysis, which gives the spatial structure of flame fluctuations. It was proved that the flame structure and excited frequency would impact the dynamic flame responses, which follows the same trend as flame transfer function. And the heat release fluctuations with the frequency of 300Hz~400Hz would be strengthened as the heat release zone moves to the shear layer between the pilot and main stages at the range of stratified ratio from 0.5 to 2.0. In summary, the advantages and effectiveness of DMD methods to diagnose the complex fluctuations of internally-staged-swirling flame are established here. Consequently the results obtained by DMD method could be helpful to the active control over the flame fluctuation.