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An axial single-stage high-speed test rig was numerically studied in this paper with half-annulus URANS simulations to describe the flow characteristics at the near stall condition. Numerical probes were arranged circumferentially near the casing in each rotor passage from the leading edge to the trailing edge evenly. Wavelet analysis was applied to demonstrate the time-frequency characteristics of the wall pressure signals captured by the probes located at different axial positions. The detailed tip flow fields and wavelet transform results were combined to depict the generation and propagation of the spike type stall inception. According to the wavelet spectrum, characteristic frequencies correspond to the temporal and spatial features of the rotating stall, such as the fluctuation of the shock wave, self-oscillation and propagation of tip leakage vortex et al. Consequently, the detection of typical spike stall inception can be significantly brought forward through identifying the crucial rotating disturbance and its development for the onset of stall inception. Then, the specific flow fields verified by previous researchers are also discussed to reveal the flow mechanism of stall inception evolution, including the leading edge spillage and the trailing edge backflow. Further investigation showed that the stall inception with smooth casing corresponds to the radial separation vortex caused by the tip leading edge spillage, which continues to develop and propagate in the circumferential direction and finally induces the stall. |
