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

非对称燃烧室壁对受限旋流燃烧器结构中热声不稳定性的影响尚未得到严格的研究，无论是数值计算还是实验，尽管其影响预计是显著的，并可能导致整个燃烧室单元的崩溃。由于燃烧室壁对燃烧过程的影响，火焰的热释放和声场之间的相互作用在方位角方向上被修改，使得热声不稳定性的形成和传播被改变。因此，将对受限旋流燃烧器结构的流体动力学和声学模式进行数值分析，以确定在轴向、径向和方位角方向上可能发生在真实的燃烧器结构中的热声不稳定性。将计算开放式旋流燃烧器以及对称和非对称受限旋流燃烧器的流场和声场，并确定旋流火焰与燃烧器壁的声学和流体力学相互作用，以及旋流火焰与自由剪切层、外部和中心回流区以及旋进涡核（PVC）的相互作用。数值研究是基于大涡模拟（LES）和解决方案的声学扰动方程，这样的热声不稳定性的基本机制，可以通过分析声源项来理解。此外，动态模式分解（DMD）的方法被用来计算的LES解决方案在频率空间中的主导模式，这样的基础上的声学和DMD分析的火焰流和火焰声相互作用可以局部确定。研究结果将导致理解的轴向，径向和方位角的热声不稳定性的上下文中的限制燃烧室系统。

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.