Abstract: For a low speed isolated axial compressor rotor, full annulus simulation model is adopted to numerically study the flow features in the rotor tip region dominated by periodical oscillation of unsteady tip leakage flow. And methods of coordinate transformation of pressure signals between the rotor relative and absolute stationary reference frames, fast Fourier transform and frequency band-pass filter are used. The modulated frequency features along blade chord in two reference frames are analyzed. For the dominated frequency component, the circumferential propagation characteristics are studied, and the evolutions of modulated frequency relation between two reference frames and circumferential propagation features during throttling process are also summarized. Further the fluid dynamic reason for the decrease of autocorrelation coefficient of pressure signals from transducer mounted on compressor casing is elucidated. It’s shown that flow features near the rotor tip end wall dominated by periodical tip leakage flow unsteadiness are the basis for the analysis and prediction of stall precursors. Selection of reference frames, position of transducers and analysis method will greatly affect the results, and multiform features can be obtained for the same flow phenomenon. The results in this paper may give some guidelines for the comparison of results between experiment and numerical simulation, and also for the uniform fluid mechanism clarification for different flow features.

Key words: Axial compressor, Circumferential propagation, Stall precursor, Tip leakage flow