An experimental study on a turbulent, swirl-stabilized backward facing step combustor is conducted to understand the spatiotemporal dynamics during the transition from combustion noise to thermoacoustic instability. By using a turbulence generator, we investigate the change in the spatiotemporal dynamics during this transition for added turbulence intensities. High-speed CH* images of the flame (representative of the field of local heat release rate fluctuations ( q · ' (x,y,t))) and simultaneous unsteady pressure fluctuations ( p ' (t)) are acquired for different equivalence ratios. In the study, without the turbulence generator, as the equivalence ratio is reduced from near stoichiometric values, we observe an emergence of coherence in the spatial dynamics during the occurrence of intermittency, enroute to thermoacoustic instability. As the turbulence intensity is increased using the turbulence generator, we find that there is an advanced onset of thermoacoustic instability. Spatial statistics and the instantaneous fields of p ' ( t ) q · ' ( x , y , t ) show that during the transition from combustion noise to thermoacoustic instability, the emergence of coherent spatial structures in the instantaneous fields of p ' ( t ) q · ' ( x , y , t ) for the experiments with higher turbulence intensities is advanced. However, as the equivalence ratio is reduced further, we notice that higher turbulence intensities result in the reduction of the strength of the pressure oscillations during the state of thermoacoustic instability. We find that, at these low equivalence ratios, there is a decrease in the coherence due to the dispersal of p ' ( t ) q · ' ( x , y , t ) , which explains the reduction in the strength of the pressure oscillations.

中文翻译：

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过渡到热声不稳定性的时空动力学：湍流强度变化的影响

为了研究从燃烧噪声到热声不稳定的过渡过程中的时空动态，对湍流，旋流稳定的后向阶梯式燃烧室进行了实验研究。通过使用湍流发生器，我们研究了在此过渡过程中时空动力学的变化，以增加湍流强度。对于不同的当量，获取火焰的高速CH *图像（代表局部放热率波动的场（q·'（x，y，t）））和同时的非稳态压力波动（p'（t））。比率。在没有湍流发生器的研究中，当当量比从近乎化学计量的值减小时，我们观察到间歇性发生期间空间动力学的相干性出现，这导致了热声不稳定性。随着使用湍流发生器增加湍流强度，我们发现热声不稳定性的发生开始提前。空间统计和p'（t）q·'（x，y，t）的瞬时场表明，在从燃烧噪声到热声不稳定性的过渡过程中，p'（t）瞬时场中相干空间结构的出现。 q·'（x，y，t）用于更高湍流强度的实验。但是，当当量比进一步降低时，我们注意到，较高的湍流强度会导致热声不稳定状态下压力振荡强度的降低。我们发现，在这些低当量比的情况下，由于p'（t）q·'（x，y，