多模态热声不稳定混沌现象实验研究

Experimental Study on Chaotic Phenomena of Multimodal Thermoacoustic Instability

热声不稳定是一种常发生在航空航天发动机中,会对发动机造成危害的现象,该现象实质上是声波与非定常热释放的相互耦合。本文设计了一个多孔预混火焰Y型里开管(Rijke管)装置,用以研究多频率非线性热声不稳定性。这种简化燃烧室结构能够很好捕捉真实发动机中由于复杂几何结构引起的多模态热声不稳定性。通过改变火焰的当量比和其在Y型里开管上游的位置,来遍历燃烧室中不同热声振荡行为,并结合短时傅里叶变换(STFT)、相空间重构等方法分析了不同非线性热声振荡行为,发现在改变工况时,会出现高频极限环状态、高频向低频的模态转换状态、低频极限环状态、准周期状态以及混沌状态等现象,而在当量比为0.94的工况下会出现两个不稳定频率模态争夺的实验现象,在实验结果基础上,深入分析了这些非线性现象的成因。

Thermoacoustic instability is a phenomenon that often occurs in aerospace engines and can cause damage to the engine.The phenomenon is essentially the mutual coupling of sound waves and unsteady heat release.A multi-frequency nonlinear thermoacoustic instability is designed in a Y-shaped open tube(Rijketube)device with a porous premixed flame.This simplified combustion chamber structure can well capture the multimodal thermoacoustic instability caused by complex geometry in real engines.By changing the equivalence ratio of the flame and its position upstream of the Y-shaped open tube,the different thermoacoustic oscillation behaviors in the combustion chamber are traversed,and the different nonlinear thermoacoustic oscillation behaviors are analyzed by using methods such as the short term Fourier transform and phase space reconstruction.It is found that high frequency limit cycle state,modal transition state from high frequency to low frequency,low frequency limit cycle state,quasi-periodic state,and chaos will appear when the working conditions are changed.Under the condition of equivalence ratio of 0.94,there will be experimental phenomena of two unstable frequency modes competing for each other.Based on the experimental results,the causes of these nonlinear phenomena are deeply analyzed.