To evaluate the complex dynamic phenomena occurring during combustion, Large Eddy Simulations of the swirl-stabilized flame of PRECCINSTA burner were carried out. The existence of a precessing vortex core in the initial stage of unsteady combustion was proved, both in the cold flow and initial stage of the combustion. The PVC flow structure finally disappeared and became a flapping toroidal flowfield structure with the increase in the amplitude of pressure oscillation when combustion instabilities occurred. The LES results indicate the interactions between the PVC and thermoacoustic coupling and the underlying mechanism of the phenomenon. This study evaluated the effect of PVC on the thermoacoustic coupling in the initial stage of unsteady combustion and elucidated the mechanism for the disappearance of PVC under large-scale pressure oscillation. This has a great significance in the practical industrial applications of controlling combustion instabilities.

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