Combustion instabilities were investigated experimentally for a hydrogen-rich combustion in a model afterburner installed at the end of a high-enthalpy wind tunnel. Air was supplied at 0.3 MPa and 950 K. The combustion instabilities were studied with the time-resolved measurements of a near-infrared (NIR) emission from water molecules over 780 nm using a high-speed video camera. Pressure was also measured in the combustor. The pressure and the NIR images were analyzed by data-driven approach, which include the fast Fourier transform (FFT), the wavelet transform, the dynamic mode decomposition (DMD) and the Gaussian process latent variable methods (GP-LVM). Thermoacoustic instability was observed under a rich condition, and the amplitude of the pressure oscillation was the maximum at the overall equivalence ratio of approximately 2.4 or 2.7 as a result of the FFT. The combustion dynamics were investigated in detail for an experimental run at the equivalence ratio of 2.4. A pressure spectrogram indicated a flame–vortex interaction with a Strouhal number of 0.5 (2300 Hz), thermoacoustic instability (560 Hz), and their transitions with the wavelet transform. For NIR images, the same tendency was also observed in the spectrogram of the modes obtained by the Gabor-filtered DMD, which could clearly resolve the high-order harmonic modes of the flame–vortex interaction and the thermoacoustic instability. Furthermore, NIR images were analyzed with GP-LVM to study the evolution of the combustion dynamics in a three-dimensional latent space. Recurrence plots with the Euclidean distance function were used to visualize the evolutions of the combustion dynamics. A limit cycle behavior of the flame–vortex interaction was clearly observed, whereas the limit cycle of the thermoacoustic instability showed more complicated behaviors. The transition behaviors of the instabilities were observed in the recurrence plots in detail, indicating that the flame–vortex interaction excited the fourth harmonic mode of the thermoacoustic instability, followed by the basic mode.

在安装在高焓风洞末端的模型加力燃烧器中，对富氢燃烧的燃烧不稳定性进行了实验研究。在0.3 MPa和950 K的空气压力下供应空气。使用高速视频摄像机对水分子在780 nm范围内的近红外（NIR）发射进行时间分辨测量，从而研究了燃烧的不稳定性。还在燃烧器中测量压力。通过数据驱动方法分析了压力和近红外图像，包括快速傅立叶变换（FFT），小波变换，动态模式分解（DMD）和高斯过程潜变量方法（GP-LVM）。在丰富的条件下观察到热声不稳定性，并且在总当量比约为2.4或2时，压力振荡的幅度最大。FFT的结果为7。对于当量比为2.4的实验运行，详细研究了燃烧动力学。压力频谱图显示了火焰-涡旋相互作用，斯特鲁哈尔数为0.5（2300 Hz），热声不稳定性（560 Hz），以及它们随小波变换的跃迁。对于NIR图像，在通过Gabor滤波的DMD获得的模式的频谱图中也观察到了相同的趋势，这可以清楚地解决火焰-涡旋相互作用和热声不稳定性的高次谐波模式。此外，使用GP-LVM对NIR图像进行了分析，以研究三维潜在空间中燃烧动力学的演变。具有欧几里得距离函数的递归图用于可视化燃烧动力学的演变。清楚地观察到了火焰-涡旋相互作用的极限循环行为，而热声不稳定性的极限循环表现出更复杂的行为。在递归图上详细观察到不稳定性的过渡行为，表明火焰-涡旋相互作用激发了热声不稳定性的四次谐波模式，随后激发了基本模式。