环形燃烧室壁温对热声不稳定性影响的实验研究

Experimental Study of Wall Temperature Effect on Thermoacoustic Instabilities in Annular Combustor

关键词:  环形燃烧室  热声不稳定性  壁温效应  预混旋流火焰  周向模式  动态模态分解

Key words:  Annular combustor  Thermoacoustic instability  Wall temperature effect  Premixed swirling flame  Azimuthal mode  Dynamic mode decomposition

摘要:

为了研究壁温效应对热声振荡的影响，基于环形燃烧室/涡轮耦合实验平台，在当量比Φ=0.82和燃烧功率P=15.5 kW的工况参数下开展了实验研究。相比于独立环形燃烧室实验，本文所引入的涡轮导叶出口组件，使得燃烧室跟发动机实际工况出口匹配情况更接近，具有更一致的热声环境和热容效应。实验发现，在壁温升高过程中伴随着不同类型热声不稳定模式间的切换以及振荡频率、幅值等参数的演变。进一步选取了6个典型状态点，结合基于火焰图像序列的动态模态分解，对比光电倍增管信号和不同方位角的声压信号，分析了各个状态点的火焰动力学和声学响应特征。实验结果表明，在固定功率和当量比工况下，受燃烧室壁面热平衡状态的影响，热声不稳定模式先后经历了由亥姆霍兹模式、1/4波纵向模式、周向混合模式和旋转模式所主导的过程。在出现周向模式的初期，其表现为旋转率呈现肥尾近均匀分布的驻波-旋转混合模式，而后期演变为旋转率分布相对集中的逆时针方向旋转模式。

Abstract:

Based on an integrated annular combustor-turbine experimental platform， the effects of wall temperature on thermoacoustic instability were experimentally studied in a fixed case with an equivalence ratio Φ=0.82 and a combustion power P=15.5kW. Compared with the typical independent annular combustor test， the outlet with the component of the turbine guide vane in this paper provided a more similar matching to an actual engine with a more consistent thermoacoustic environment and heat capacity. In the experiment， mode switching between different thermoacoustic modes was captured， and the corresponding modal frequencies and amplitudes greatly changed with the increasing wall temperature. Six typical state points were selected to analyze the flame dynamics and acoustic characteristics. The dynamic modal decomposition results based on the flame high-speed image sequences were compared with the photomultiplier tube signals and the acoustic pressure signals at different azimuth angles for each state point. The experimental results showed that even under the condition of a fixed combustion power and equivalent ratio， the dominated mode was changing due to the wall temperature effect： from a Helmholtz mode to a 1/4 wave longitudinal mode， to an azimuthal standing wave mode， and finally to an azimuthal spinning wave mode. The azimuthal modes acted as the standing-spinning mixed mode with fat-tailed distributions of the spin ratio in the beginning and then transformed into a counterclockwise spinning mode with relatively concentrated distributions of the spin ratio.