Abstract This paper addresses the mechanisms through which transverse acoustic oscillations excite unsteady heat release. Forced and self-excited transverse acoustic instability studies to date have strong coupling between the transverse and axial acoustic fields near the flame. This is significant, as studies suggest that it is not the transverse disturbances themselves, but rather the induced axial acoustic disturbances, that control the bulk of the heat release response. This paper presents results from an experiment that controls the relative amplitudes of transverse and axial disturbances and measures the flow field and heat release response for an acoustically compact, swirling flame. 5 kHz, simultaneous sPIV and OH-PLIF measured the flow field and flame edge, and OH* chemiluminescence measured the relative heat release. Experiments performed with essentially the same transverse acoustic wave field, but with and without axial acoustics, show that significant heat release oscillations are only excited in the former case. The results show that the axial disturbances are the dominant cause of the heat release oscillations. These observations support the theory that the key role of the transverse motions is to act as the “clock” for the instability, setting the frequency of the oscillations while having a negligible direct effect on the actual heat release fluctuations. They also show that transverse instabilities can be damped by either actively canceling the induced axial acoustics in the nozzle (rather than the much larger energy transverse combustor disturbances), or by passively tuning the nozzle impedance to drive an axial acoustic velocity node at the nozzle outlet.

中文翻译：

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轴向声学在横向声学火焰响应中的作用

摘要 本文讨论了横向声学振荡激发非稳态放热的机制。迄今为止，强制和自激横向声不稳定性研究在火焰附近的横向和轴向声场之间存在强耦合。这很重要，因为研究表明，控制大部分热释放响应的不是横向扰动本身，而是引起的轴向声扰动。本文介绍了一项实验的结果，该实验控制横向和轴向扰动的相对幅度，并测量声学紧凑的旋转火焰的流场和热释放响应。5 kHz，同步 sPIV 和 OH-PLIF 测量流场和火焰边缘，OH* 化学发光测量相对热释放。使用基本相同的横向声波场进行的实验，但有和没有轴向声学，表明显着的热释放振荡仅在前一种情况下被激发。结果表明，轴向扰动是引起放热振荡的主要原因。这些观察结果支持横向运动的关键作用是充当不稳定的“时钟”的理论，设置振荡的频率，同时对实际放热波动的直接影响可以忽略不计。他们还表明，横向不稳定性可以通过主动抵消喷嘴中引起的轴向声学（而不是能量大得多的横向燃烧器扰动）来抑制，