To analyze inter-stage interaction and transient flow characteristics in a multistage centrifugal pump, numerical simulations of both steady and unsteady, three-dimensional turbulent flow in a two-stage centrifugal pump are conducted. Pressure fluctuations at monitoring points in both the impeller and diffuser passages are obtained at different flow rates. The results show that the first-stage diffuser is the key factor for determining the non-uniform velocity distribution at the inlet of the second-stage impeller. There is a strong rotor-stator interaction between the impeller outlet and diffuser inlet in each stage. Even though the geometrical shape of the whole flow passage is so complicated, the blade pas-sing frequency is still the dominating factor that decides the pressure fluctuation characteristics in the entire flow passage in the pump. By contrast, the pressure fluctuations are less affected by the number of diffuser vanes. The pressure fluctuation amplitude at the blade passing frequency within the impeller passages increases gradually from the impeller inlet to the outlet, but vice versa in the diffuser. The pressure fluctuation amplitude at the blade passing frequency is still dominated at low and high flow rates, however, the fluctuation amplitude is amplified, especially at the low flow rate.
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