The rotating instability in a contra-rotating axial flow compressor is investigated by experiments. Twenty-four pressure sensors were installed on the casing to capture the unsteady flow in the rotor tip region simultaneously. A double-phase-locking technique suitable for the contra-rotating compressor was proposed to characterise the static pressure contours of the rotor tip. The mean and root-mean-square pressure contours indicate that rotating instability occurs before the rotating stall happened, and the rotor tip clearance vortex is located upstream of the rear rotor leading edge plane before stall. Fourier spectrum shows that rotating instability and rotating stall both happened under the stall condition, and the frequency band of rotating instability does not change with the flow rate. In the front rotor, the frequency of rotating instability is half of the blade passing frequency. It is verified that the modal estimation method can be implemented by using the average azimuthal phase velocity, which significantly reduced the number of pressure sensors required. Modal estimation results show that each peak of the rotating instability frequency band corresponds to a unique dominant circumferential mode. By optimising average azimuthal phase velocity, an improved modal estimation method is obtained, which can further improve the reliability of the modal estimation results.

中文翻译：

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对转轴流压气机旋转不稳定性的实验研究

通过实验研究了对转轴流压气机的旋转不稳定性。外壳上安装了 24 个压力传感器，以同时捕获转子尖端区域的非定常流动。提出了一种适用于对转压气机的双锁相技术来表征转子叶尖的静压轮廓。均值和均方根压力等值线表明，旋转失速发生在旋转失速之前，转子叶尖间隙涡位于失速前后转子前缘平面的上游。傅里叶谱表明，在失速条件下，旋转失稳和失速均发生，旋转失稳的频带不随流量变化。在前转子中，旋转不稳定的频率是叶片通过频率的一半。经验证，模态估计方法可以通过使用平均方位相速度来实现，显着减少了所需的压力传感器数量。模态估计结果表明，旋转不稳定频带的每个峰值对应一个独特的主导圆周模态。通过优化平均方位相速度，得到改进的模态估计方法，可以进一步提高模态估计结果的可靠性。模态估计结果表明，旋转不稳定频带的每个峰值对应一个独特的主导圆周模态。通过优化平均方位相速度，得到改进的模态估计方法，可以进一步提高模态估计结果的可靠性。模态估计结果表明，旋转不稳定频带的每个峰值对应一个独特的主导圆周模态。通过优化平均方位相速度，得到改进的模态估计方法，可以进一步提高模态估计结果的可靠性。