多模态热声不稳定混沌现象实验研究

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.