Flame-generated nanoparticles, such as soot, caused by the incomplete combustion of hydrocarbon fuels in reacting flows, have adverse effects on human health and the environment. Understanding the interaction between soot and flow dynamics is critical to reducing particle emissions from engine combustors. This is because soot formation and evolution are highly sensitive to the flow dynamics encountered, especially in confined turbulent swirling flows, where strong shear layers and recirculation regions introduce complex, coherent patterns of both fast and slow timescales. These patterns are often crucial for understanding soot evolution and for controlling its formation and emission. To this end, large-eddy simulations (LES) of an aeroengine model combustor, with and without dilution jets, are conducted using state-of-the-art soot models. Then, modal analysis of flow and soot dynamics in the combustor is performed using the spectral proper orthogonal decomposition (SPOD) method with transient LES data. To the best of the authors' knowledge, this work is the first study to utilize SPOD and raw LES data to reveal the dynamics of coherent structures in swirl sooting flames. The frequency bands of both high-frequency dynamics (HFD, 234.375–468.75 Hz) and low-frequency dynamics (LFD, 0–156.25 Hz) are identified without any prior filtering. It is found that HFD primarily exists in the shear layer and inner recirculation zone, whereas LFD is present throughout the entire combustor. Compared to LFD, the HFD has a significant impact on velocity and gas-phase soot precursors (PAH), while LFD plays a crucial role in soot evolution. Furthermore, the results show that the evolution of velocity, PAH, and soot is closely coupled within the LFD frequency band. It is found that for soot and PAH, the impact of dilution jets on HFD modes is minor and on LFD modes is significant, while the opposite trend is observed for velocity modes.

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• Combustion
• Reacting flows