速度脉动下分层旋流火焰动态传播结构提取

Extraction of Propagation Structure on Stratified Swirl Flame Dynamics under Velocity Fluctuation

关键词:  航空发动机燃烧室  分层旋流火焰  重定向POD  传播结构  燃烧不稳定性

Key words:  Aero-engine combustor  Stratified swirl flame  Re-oriented POD  Propagation structure  Combustion instability

摘要:

为了深刻理解分层旋流火焰的动态结构，开展了分层旋流火焰动态的模态分析和参数化研究。实验在BASIS （北京航空航天大学发展的具有台阶隔离段的独立分层旋流燃烧器）上开展，以甲烷为燃料预混燃烧，使用高速摄像捕捉了速度脉动下的CH*化学发光信号动态图像。利用传统的本征正交分解（POD）和重定向POD分析了火焰动态特性，并利用重定向POD提取了火焰动态中沿着轴向和径向的周期性传播结构，传播结构的频率与速度脉动频率保持一致，且轴向模态的传播结构最为明显。同时，研究了总当量比对重定向POD模态的影响，分析表明：总当量比增大时，重定向POD模态的拓扑结构会发生变化；重定向POD模态中出现了错位现象，这种现象与相平均图像中的火焰传播行为保持一致。重定向POD方法能够有效提取旋流火焰动态中的传播结构，为旋流火焰燃烧不稳定性的机理研究提供了一种分析工具。

Abstract:

In order to deeply understand the dynamic structures of stratified swirl flame，the mode analysis and parametric study on stratified swirl flame dynamics are carried out. The experiment was carried out on BASIS（Beihang Axial Swirler Independently Stratified burner）， fueled with premixed methane， and using the high-speed camera to capture the flame dynamics of CH* chemiluminescence signal under velocity fluctuation. The characteristics of flame dynamics are analyzed by using traditional proper orthogonal decomposition （POD） and re-oriented POD. The periodic propagation structure along the axial and radial direction is obtained by re-oriented POD. The results show that the frequency of propagation structure is consistent with that of velocity fluctuation， and the propagation structure of axial mode is the most obvious. Then， the effects of the overall equivalence ratio on the re-oriented POD mode are studied. When the overall equivalence ratio increaes， the topological structure of re-oriented POD mode changes. And the dislocation phenomenon appears in the re-oriented POD mode， which is consistent with the flame propagation behavior in the phase average images. This paper shows that the re-oriented POD method can effectively extract the propagation structure in the swirl flame dynamics， which provides an analysis tool for the mechanism study of combustion instability of swirl flame.