To investigate the flame dynamics in an annular combustor with multiple swirl injectors, a 3D large-eddy simulation (LES) with level-set flamelet turbulent combustion model was implemented. The formulation consists of the Favre-filtered conservation equations of mass, momentum, and energy. Turbulent combustion is modeled by the level-set approach with laminar flamelet library. The GRI-MECH 3.0 mechanism and presumed-PDF are used to obtain the combustion chemistry. The combustor of concern is an annular combustor which is modified from the LM6000 single rectangular combustor. The unsteadiness of the flow structure and the flame dynamics in the combustor are analyzed using Proper Orthogonal Decomposition (POD). Three important characteristic of swirling flow are visualized: diversity, vortex procession with decreasing strength, and vortex breakdown. It is shown that the turbulent motion of the swirl flow directly affects acoustic oscillation and flame dynamics through the spectral analysis. The six most dominant acoustic frequencies are extracted from the flow field by the POD analysis. The typical radial and tangential modes are dominant.
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