Identification of Combustion Noise and Flame Dynamics of Confined Turbulent Flames

燃烧噪声是燃烧过程中不受欢迎的副产品，由火焰的不稳定热释放速率产生。对于受限湍流火焰，可以区分两种贡献：一方面，速度或燃料浓度的湍流涨落作为源项产生放热的宽带涨落。另一方面，火焰可能会受到撞击火焰的声波的干扰。这种声-火焰相互作用一般由系统的火焰传递函数(FTF)或相应的散射矩阵来描述。一般来说，如果不知道火焰动力学(用散射矩阵或FTF表示)，就不可能准确地确定源项，反之亦然。此外，燃烧室中的声压级不仅由噪声源决定，还与火焰动力学有关。因此，对受限的湍流火焰进行全面的热声表征需要确定燃烧噪声源以及散射矩阵或FTF。拟议项目的总体目标是通过将先进的系统识别(ASI)技术与实验或大涡模拟相结合，开发能够同时确定燃烧噪声源和火焰动力学的方法。其主要思想在于用基于Box-Jenkins结构的多项式方法对火焰动力学和燃烧噪声进行建模。该模型可以看作是有限脉冲响应(FIR)方法的推广。这将使预测受限、湍流火焰的燃烧噪声成为可能，即使在声学-火焰相互作用很重要的情况下--现有方法无法很好地处理这种情况。此外，在燃烧噪声水平较高的情况下，ASI将提高FTF或散射矩阵识别的准确性和稳健性。

Combustion noise is an undesirable by-product of combusion processes, generated by unsteady heat release rate of the flame. For confined turbulent flames, two contributions can be distinguished: On the one hand, turbulent fluctuations of velocity or fuel concentration generate as a source term broad-band fluctuations of the heat release. On the other hand, the flame may be disturbed by acoustic waves impinging upon the flame. This acoustic-flame interaction is generally described by the flame transfer function (FTF) of the system, or by the corresponding scattering matrix. In general it is not possible to determine accurately the source terms without knowledge of the flame dynamics (as expressed in terms of the scattering matrix or the FTF), and vice versa. Furthermore, the sound pressure levels in a combustion chamber are determined not only by the noise sources, but also the flame dynamics. Thus comprehensive thermo-acoustic characterization of confined, turbulent flames requires to determine both the combustion noise source as well as the scattering matrix or FTF. The overall objective of the proposed project is to develop methods that allow the concurrent determination of the combustion noise source and the flame dynamics by combining advanced system identification (ASI) techniques with experiment or large eddy simulation. The main idea consists in modelling both flame dynamics and combustion noise by a polynomial approach based on the Box-Jenkins structure. This model may be considered as an extension of Finite Impulse Response (FIR) methods. This will make possible to predict combustion noise of confined, turbulent flames even in situations where acoustic-flame interactions are important -- a case that cannot be handled well by existing methods. Furthermore, ASI will increase the accuracy and robustness of FTF or scattering matrix identification in situations where combustion noise levels are high.