This paper presents a detailed comparative analysis and discussion of two typical predictive methods for combustion instability in long flame combustion chambers: the coupled method and the decoupled method. Using large eddy simulation (LES), the coupled method directly predicts stability in typical long flame combustion chambers. In the decoupled method, stability in the combustion chamber is predicted by combining a low-order acoustic network for long flames with flame responses and mean parameters from numerical simulations. The research results indicate that the coupled method provides full-field information, while the decoupled method neglects certain factors, such as the coupling between combustion and acoustics. However, the decoupled method can directly determine combustion instability based on the growth rate of oscillation modes. The flow field undergoes periodic changes, with the region of fluctuation in the combustion heat release rate gradually increasing, resembling vortex development, which ruptures upon encountering the wall due to radial constraints. Furthermore, in the decoupled method, the periodic changes in the flow field are controlled by the frequency of incoming flow disturbances, whereas in the coupled method, they are controlled by the acoustic frequency of the combustion chamber. In the coupled method, the coupling among disturbances and the acoustic disturbances at the boundaries amplifies the disturbances, causing the radial scale of the fluctuation region in the combustion heat release rate to increase along the axial direction and approach a fixed value faster than in the decoupled method.

中文翻译：

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关于长火焰燃烧室燃烧不稳定性预测的两种方法


本文对长火焰燃烧室中燃烧不稳定性的两种典型预测方法：耦合法和解耦法进行了详细的比较分析和讨论。使用大涡模拟 （LES），耦合方法直接预测典型长火焰燃烧室中的稳定性。在解耦方法中，通过将长火焰的低阶声学网络与火焰响应和数值模拟的平均参数相结合来预测燃烧室的稳定性。研究结果表明，耦合方法提供了全场信息，而解耦方法忽略了某些因素，例如燃烧与声学之间的耦合。然而，解耦方法可以根据振荡模式的增长率直接确定燃烧不稳定性。流场发生周期性变化，燃烧热释放速率的波动区域逐渐增加，类似于涡流发展，由于径向约束，在遇到壁时破裂。此外，在解耦方法中，流场的周期性变化由输入流扰动的频率控制，而在耦合方法中，它们由燃烧室的声频率控制。在耦合方法中，扰动之间的耦合与边界处的声扰动放大了扰动，导致燃烧热释放速率波动区域的径向尺度沿轴向增加，并比解耦方法更快地接近固定值。