同轴离心式喷嘴热声不稳定性递归分析

Recurrence Analysis of Thermoacoustic Instabilities of an Coaxial Swirl Injector

为获得同轴离心式喷嘴燃烧动力学特性,开展了喷注单元稳定性试验研究。试验中燃料流量不变,随氧化剂流量增加,热声系统依次经历了燃烧噪声状态、阵发状态和准周期振荡状态。采用递归方法对实验结果进行分析。首先,利用交互信息法和虚假最邻近法分别求解最优延迟时间和嵌入维数,获得了典型工况下的相空间轨迹图。其次,递归图分析表明系统出现了第II类阵发现象,意味着系统发生了亚临界Hopf分叉,与实验结果一致。最后,递归量化分析表明,确定率可以将阵发状态和准周期振荡状态与燃烧噪声状态区分出来,并可以对热声振荡进行预报。

An experimental investigation on the nonlinear combustion dynamics of a laboratory-scale coaxial swirl injector in a cylindrical combustor is carried out. For a constant kerosene flow rate, the dynamic behavior transits from combustion noise to quasiperiodic oscillations via intermittency with increasing mass flow rate of oxygen diluted with air. The phase space is reconstructed from an experimental pressure time series with the optimal delay time and the embedded dimension calculated using the mutual information approach and false nearest neighbors approach respectively. The structures for the type-II intermittency are found in the recurrence plots, which are due to the subcritical Hopf bifurcation and validated experimentally in our previous work. The recurrence quantification analysis reveals that the determinism shows relatively higher values in the intermittent and quasiperiodic oscillations regimes as compared to the combustion noise regimes. It is concluded that the determinism is able to detect the transitions in a turbulent combustor and hence can be used as the early warning signals of the thermoacoustic instabilities.