The thermo-acoustic instability behavior of non-premixed hydrogen combustion is analyzed in the present work with the inlet Reynolds number, Re as the control parameter. It is observed that the dominant frequency (mode) shifts from the fundamental duct-acoustic mode to the first harmonic, as Re is varied. Continuous wavelet transform of the pressure oscillations reveals that at different Re, the dynamical nature of oscillations is topologically different, although they have identical spectral content. An interesting dynamical behavior identified as two-period quasi-periodic oscillations is observed, which has not been reported in prior literature. The state is seen to be unstable to incremental changes in Re and transitioning to limit cycle oscillations subsequently. Further diagnosis employing time-resolved OH* chemiluminescence and particle image velocimetry reveals the amplitude modulation of the quasi-periodic oscillation as a result of staggered vorticity distribution across the bluff body which results in asymmetric heat release rate distribution. A general framework for such oscillations is then applied, leading to identifying specific conditions that need to be satisfied to enable the existence of these oscillations. This study leads to novel observations on the asymmetric nature of shear layers, which can result in hitherto observed dynamical states.

Graphic abstract

中文翻译：

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湍流氢燃烧室中两周期准周期振荡的实验分析

本文以进口雷诺数Re为控制参数，对非预混氢气燃烧的热声不稳定性行为进行了分析。可以观察到，随着Re的变化，主频率（模式）从基本的管道声学模式转变为一次谐波。压力振荡的连续小波变换表明，尽管Re具有相同的频谱含量，但在不同的Re处，振荡的动力学性质在拓扑上是不同的。观察到一种有趣的动力学行为，被认为是两周期的准周期振荡，这在现有文献中尚未见报道。可以看出该状态对于Re的增量变化不稳定，随后过渡为限制周期振荡。使用时间分辨的OH *化学发光和颗粒图像测速仪进行的进一步诊断显示，由于在非流线形体上错开的涡度分布，导致了准周期性振荡的振幅调制，这导致了不对称的放热速率分布。然后应用这种振荡的通用框架，从而确定需要满足的特定条件以使这些振荡的存在。这项研究导致对剪切层的不对称性质的新颖观察，这可能导致迄今观察到的动力学状态。然后应用这种振荡的通用框架，从而确定需要满足的特定条件以使这些振荡的存在。这项研究导致对剪切层的不对称性质的新颖观察，这可能导致迄今观察到的动力学状态。然后应用这种振荡的通用框架，从而确定需要满足的特定条件以使这些振荡的存在。这项研究导致对剪切层的不对称性质的新颖观察，这可能导致迄今观察到的动力学状态。

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