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

不对称燃烧室壁面对受限旋流燃烧器结构热声不稳定性的影响还没有得到严格的数值和实验研究，尽管它的影响预计是显著的，并可能导致整个燃烧室单元的崩溃。由于燃烧室壁面对燃烧过程的影响，在方位角方向上改变了火焰放热与声场的相互作用，从而改变了热声不稳定性的形成和传播。因此，将对密闭涡流燃烧器配置的流体动力学和声学模式进行数值分析，以确定在实际燃烧器配置中在轴向、径向和方位角方向上可能发生的热声不稳定性。计算了开式旋流燃烧器以及对称和非对称密闭旋流燃烧器的流场和声场，识别了旋流火焰与燃烧室壁面、与自由剪切层、外循环区和中心循环区以及加工涡芯（PVC）的声学和流体力学相互作用。数值研究是基于大涡模拟（LES）和声扰动方程的解，这样可以通过分析声源项来理解热声不稳定性的基本机制。在此基础上，利用动态模态分解（DMD）方法在频率空间中计算了LES解的主模态，从而在声学和DMD分析的基础上，局部确定了火焰-流和火焰-声相互作用。这些发现将有助于理解密闭燃烧室系统中轴向、径向和方位的热声不稳定性。

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.