Abstract：The flow field in an axial-flow pump at different inlet pressure conditions including cavitating and non-cavitating conditions was simulated by using the computational fluid dynamics(CFD)approach based on theory of bubble dynamics and steam-liquid two-phase flow．The velocity field and pressure
distribution were analysed during cavitation progress and the pump characteristics were predicted．The results show that under the non—cavitating condition，the pump head-flow relationship is well predicted with an inaccuracy within 2％．While under the cavitating condition。the cavitation occurring and develo-ping processes are captured successfully by CFD simulation．The cavitation directly affects the pressure distribution on impeller blade surfaces，and also results in change of the pump head and power eharacteristics．Under the cavitation condition，the cavitation area can be found at the leading edge of the guidevane suction sides．Similarity of the cavitation distribution are found among the different impeller passages．But significant differences of the cavitation distribution are revealed among the different guide vanepassages．which is one of the primary factors that result in unstable operation of an axial-flow pump．
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