On the basis of air heater characteristics, a new computational model was developed in this paper, which was aimed at investigating acoustics and instabilities in air heaters. This model included the effects of mean flow, viscosity, entropy waves, non-linear acoustics and realistic boundary conditions. In addition, it was practical for air heaters with hundreds of injectors, complex configurations and geometries. Analytical solutions of acoustics in a closed rectangular cavity were used to verify and validate the computational model. It was shown that the predicted critical parameters of air heater agreed well with the experimental data or design values. This model predicted the self-excited spinning tangential modes without any preliminary assumptions about them. Traditional combustion response function assumes that combustion mainly takes place in a so-called rapid combustion zone, and this zone is usually modelled as a disc in the combustor near the injection head. However, in practice, the flame has a spatial distribution. This paper described the effect of flame spatial distribution on predictions of oscillation frequency and mode. It was found that frequency and mode shape of oscillations closely depended on the length of the heat release zone. Comparison of different heat release zones indicated that the increment of heat release length exhibited an increased tendency toward lower-order longitudinal modes, when the heat release zone was located near the faceplate where it was the pressure antinode of the longitudinal mode. Modulation of heat release length might cause bifurcations between standing and turning modes. A noticeable tendency was toward higher-order standing tangential mode with increasing heat release length. Finally, theoretical analysis of the modal behaviour, i.e. standing or spinning waves, was performed.

中文翻译：

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用新的计算模型计算空气加热器燃烧不稳定性

基于空气加热器的特性，本文开发了一种新的计算模型，旨在研究空气加热器的声学和不稳定性。该模型包括平均流量、粘度、熵波、非线性声学和现实边界条件的影响。此外，它还适用于具有数百个喷射器、复杂配置和几何形状的空气加热器。使用封闭矩形腔内的声学解析解来验证和验证计算模型。结果表明，预测的空气加热器关键参数与实验数据或设计值吻合良好。该模型在没有任何初步假设的情况下预测了自激旋转切向模式。传统的燃烧响应函数假设燃烧主要发生在所谓的快速燃烧区，该区通常被建模为靠近喷射头的燃烧器中的一个圆盘。然而，在实践中，火焰具有空间分布。本文描述了火焰空间分布对振荡频率和模式预测的影响。发现振荡的频率和振型与热释放区的长度密切相关。不同放热区的比较表明，当放热区位于面板附近且为纵模的压力波腹时，放热长度的增加呈现出向低阶纵模增加的趋势。热释放长度的调制可能会导致站立和转动模式之间的分叉。一个明显的趋势是随着热释放长度的增加，向更高阶的常设切线模式发展。最后，进行了模态行为的理论分析，即驻波或旋转波。