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Role of induced axial acoustics in transverse acoustic flame response

机译：轴向感应声在横向声火焰响应中的作用

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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.
机译：本文探讨了横向声振动激发不稳定的热释放的机理。迄今为止，强迫和自激的横向声不稳定性研究在火焰附近的横向和轴向声场之间具有很强的耦合性。这是很重要的，因为研究表明，控制大部分放热响应的不是横向干扰本身，而是感应的轴向声干扰。本文介绍了一个实验的结果，该实验控制横向和轴向扰动的相对幅度，并测量声学上紧凑的旋转火焰的流场和放热响应。在5kHz时，同时sPIV和OH-PLIF测量了流场和火焰边缘，而OH *化学发光测量了相对热释放。在基本相同的横向声波场上进行的实验，无论是否带有轴向声波，都表明只有在前一种情况下才会激发明显的放热振荡。结果表明，轴向扰动是热释放振荡的主要原因。这些观察结果支持这样的理论，即横向运动的关键作用是充当不稳定性的“时钟”，设置振荡频率，同时对实际的热量释放波动具有可忽略的直接影响。他们还表明，可以通过主动消除喷嘴中感应的轴向声（而不是更大的能量横向燃烧器扰动）或通过被动调整喷嘴阻抗以驱动喷嘴出口处的轴向声速节点来抑制横向不稳定性。 。

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