In this paper, both static and dynamic experiments were conducted on a low speed counter-rotating axial fan (CRAF) to investigate its stall process. The casing pressures adjacent to the rotor tip clearance were recorded using arrays of dynamic transducers along the chordwise and circumferential directions. Special chokes were installed at the input and output of the frequency controller to suppress the electromagnetism interference, and digital filters were designed to select the desired components. The frequency spectrum analysis shows that the frequencies of the stall inception and the fully developed stall cells are not exactly the same with the value of 46% and 50% of the rotor rotational frequency. Conclusions can be drawn from the wavelet analysis that the stall inception of the CRAF turns out to be modal inception, and the stall firstly occurs on the second rotor. The propagation of stall cells is shown in the time domain map which indicates that only one stall cell exists.

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