Surge can lead to violent flow fluctuations in the compression system and damage to the blade structures. In this paper, a fully three-dimensional numerical model of the centrifugal compressor surge is developed, and the accurate transient flow evolutions in different components during the surge are studied in detail. The results show that in the surge initiation, the pressure distortion caused by the asymmetric geometry of the volute at the diffuser outlet transfers along blade passages to the impeller inlet, which induces two types of stall cells with different rotating speeds and sizes developing independently in two isolated circumferential positions at the impeller inlet. With the surge development, the two types of stall cells come into contact and are mixed, which causes the asymmetric local reverse flow near the casing of the impeller leading edge. Subsequently, the reverse flow extends to the full annuls at the impeller inlet, and the compressor pressure ratio falls abruptly. At the same time, several expansion waves arise in the impeller and travel downstream along the volute and the outlet pipe. As reflected by the nozzle, these expansion waves travel back upstream into the impeller. The findings of this research have great implications for the asymmetric flow control methods which develop novel asymmetric geometries to counteract the influence of the volute and extend the compressor stable operation range.

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