<p>Rotating Instability (RI) is a kind of pressure fluctuation phenomenon occurring on the compressors with a large tip clearance under low flow rate condition, featuring a broad hump and side-by-side peaks below the Blade Passing Frequency (BPF) in casing wall pressure spectrum. The clearance noise (CN) generated by RI has been widely concerned by academia. This paper presents an experimental and numerical investigation on the noise characteristics of RI phenomenon in a low-speed axial compressor rotor, which endures RI at several working conditions. The experiment was performed in an anechoic chamber in Shanghai Jiao Tong University. Using the results of microphones and pressure transducers distributed both in the far field and near field, the RI phenomenon was clearly identified. Thus, based on spatial Fourier transform a mode decomposition was applied so that the noise characteristics of RI can be obtained. The results show that the azimuthal acoustic modes of CN correspond to the BPF-RI modes, which is in accordance with previous literature. Then, a numerical simulation through Unsteady Reynolds-Averaged Navier Stocks (URANS) method to the entire blade row was applied. The tonal noises generated by RI are extracted by applying Green’s function to the CFD results. The acoustic simulation results are in good agreements with the experiments results both in the time and frequency domain. By analyzing the pressure contour and acoustic results, the noise characteristics during RI are presented and the connection between RI and the induced tonal noise is revealed. It is shown that tip leakage vortices form near the leading edge of blades, then travel to and impinge on the pressure side of the passage. After that the vortices break and reflect to the downstream. The impingement of the vortices together with the reflection pressure wave increases the surface pressure fluctuation on blades, has a huge influence on the noise characteristics of RI in this compressor, and eventually leads to the complicated acoustic modes.</p>

Investigation on mode characteristics of rotating instability and rotating stall in an axial compressor

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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