部分预混燃烧室热声不稳定及火焰结构实验分析

为探明旋流部分预混燃烧室热声不稳定特性及其与火焰结构关系，进行了自激热声实验。采用重构相图解析压力脉动、采用瑞利指数表征其与热释放率脉动关系、采用本征正交分解获得火焰相干结构。结果表明:随当量比增加，压力脉动呈现低振幅脉动、间歇振荡、极限环振荡和低振幅脉动，脉动频率受腔体1阶纯声学模态（特征频率约80.8 Hz）控制。未发生振荡，瑞利指数维持在零值；热声不稳定时，瑞利指数在零值以上。本征正交分解表明，极限环振荡，前2阶模态（模态能量占比55%以上）火焰分布沿纵向发生变明和变暗交替变化，由连续涡脱落导致，且模态时间系数频率83.2 Hz与压力脉动频率83.3 Hz一致；低当量比，模态无明显空间分布规律；间歇振荡，主导模态为火焰轴对称热释放率变化；高当量比，火焰仅外边缘沿纵向发生大尺度脉动。 

Investigation of thermo-acoustic instabilities and flame structures in a partially premixed combustor

Self-excited instability experiments were performed to investigate the thermo-acoustic instabilities and their relationship with heat release rate fluctuations in swirled partially premixed combustors. The reconstructed phase space was used to figure out the pressure fluctuations, and their relationship was analyzed by using Rayleigh index. The proper orthogonal decomposition method was employed to extract flame coherent structures. Results indicated that pressure fluctuations presented evolutions of low-amplitude, intermittent, limit cycle and low-amplitude oscillations, with the increase of equivalence ratio. The fluctuation frequency was controlled by the first order pure acoustic mode of the cavity (eigenfrequency was around 80.8 Hz). The Rayleigh index was around zero value when oscillations occurred, while this parameter maintained positive at the thermo-acoustic instability state. The proper orthogonal decomposition results showed that the flame distributions reflected by the first two order modes (the total energy of these two mode was above 55%) became bright and dark alternately along the longitudinal direction at the limit cycle, resulting from continuous vortex sheddings. The frequency of time coefficients (83.2 Hz) was consistent with that of pressure pulsations (83.3 Hz). At the low equivalence ratio, the mode spatial distribution had no regular pattern. When oscillations were intermittent, the dominant mode was of an axisymmetric pattern. Only the outer edge of the flame had large-scale longitudinal motions at a high equivalence ratio.