An experimental investigation on the compressor surge phenomenon was carried out in a small multi-stage axial compressor under different rotor speeds. The dynamic pressure signals of 1st rotor tip were measured by the Kulite dynamic pressure transducers and the fast response pressure probes. Results indicated that

at mid and higher rotor speed

the modal wave appears and evolves into rotating stall in the pre-surge period and

subsequently

the compressor is rapidly brought to deep surge by the huge blockage of the stall cell; However

at lower rotor speed

the classical surge is directly triggered by modal wave with the existence of rotating stall in the surge cycle.