Numerical Investigation of Noise Generation and Noise Propagation of Coated Turbulent Swirl Flames

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The influence of an asymmetric combustor wall on thermoacoustic instabilities in confined swirl burner configurations has not been studied rigorously, neither numerically nor experimentally, although its impact is expected to be significant and could lead to a collapse of the whole combustor unit. Due to the influence of the combustor wall on the combustion process the interaction between the heat release of the flame and the acoustic field is modified in the azimuthal direction such that the formation and propagation of thermoacoustic instabilities are altered. Therefore, numerical analyses of fluid dynamical and acoustical modes of confined swirl burner configurations will be performed to identify thermoacoustic instabilities that can occur in real combustor configurations in the axial, radial, and azimuthal direction. The flow field and the acoustic field of open swirl burners as well as symmetric and asymmetric confined swirl burners will be computed and the acoustical and fluid mechanical interaction of the swirl flames with the combustor wall and its interaction with the free-shear layers and the external and central recirculation zones and the precessing vortex core (PVC) will be identified. The numerical investigations are based on large-eddy simulations (LES) and solutions of the acoustic perturbation equations such that the essential mechanisms of thermoacoustic instabilities can be understood by analyzing the acoustic source terms. Furthermore, the dynamic mode decomposition (DMD) method is used to compute the dominant modes of the LES solutions in the frequency space such that based on the acoustic and the DMD analyses the flame-flow and flame-acoustic interaction can be locally determined. The findings will result in understanding the axial, radial, and azimuthal thermoacoustic instabilities in the context of confined combustor systems.