Simultaneous 10 kHz PIV/OH-PLIF/chemiluminescence and conjoint data analysis approach for thermoacoustic oscillation near lean blowout

Simultaneous multi-parameter experimental data characterizing the flow-combustion interaction process are of great significance for understanding the flame instability mechanism in combustion systems. In this study, we present simultaneous high-speed particle image velocimetry (PIV), OH planar laser-induced fluorescence (OH-PLIF), chemiluminescence, and acoustic pressure measurements of lean blowout (LBO) flames contained within a dual swirl-stabilized combustor to analyze the thermal-fluid-acoustic multi-field coupling process. The instability transition behavior and generation process of thermoacoustic oscillations near-LBO are experimentally investigated and analyzed. We identify two unstable swirling flame conditions, the transition and near-LBO, based on the dynamic behaviors of the dual flames, with significant thermoacoustic instability characteristics observed near 570 Hz through microphone measurements. Additionally, we investigate the spatiotemporal evolution of heat release and flow structure oscillations using spectral proper orthogonal decomposition (SPOD). As the flame approaches LBO, the axial vibration mode becomes predominant in both heat release and flow oscillation processes, with flow instability primarily concentrated in the flame arm zone. A joint analysis of SPOD data from PIV and chemiluminescence reveals an in-phase coupling between the flow field and heat release fluctuations, providing direct evidence of the triggering mechanism for thermoacoustic oscillations near LBO. Furthermore, the time-frequency analysis results illustrate the chronological sequence and causality between acoustic oscillations and heat release fluctuations during the LBO process.