Study on entropy wave production and dissipation in partially premixed swirl flames subject to inlet perturbations

To reveal the generation and evolution mechanisms of entropy wave in partially premixed swirl combustion, this study employed the LES-FGM method with methane fuel to systematically investigate the generation and dissipation of entropy wave under periodic excitation at the air inlet, focusing on effects of excitation frequency, amplitude, and equivalence ratio. The results show that entropy wave dynamics depend primarily on upstream flow processes, influenced by periodic vortex shedding and breakup, wall confinement, inner recirculation zone structure, and shear flow. Under 60 Hz excitation, the entropy wave maintains high stability, with approximately 1% disturbance which still observable at the combustion chamber outlet; at 100 Hz, shear flow and recirculation disperse waves, reducing perturbation to about 0.5%, demonstrating low-pass filtering characteristics. Increasing excitation amplitude induces lean-rich combustion transitions, leading to nonlinear amplitude response and further attenuation to about 0.25%. Low equivalence ratio increases flow disorder, reducing wave amplitude and distorting waveform. POD analysis reveals non-planar entropy wave characteristics especially under high-frequency excitation or low equivalence ratios, highlighting limitations of the planar wave assumption in entropy noise modeling. This work elucidates entropy wave evolution and swirl flow coupling which can support entropy noise prediction and combustor stability design.