To understand the influence of radial clearance between impeller and diffuser on flow field in two side chambers and optimize hydraulic performance even better, a cantilevered multistage centri-fugal pump was selected as a study model. The flow field in the pump side chambers were analyzed based on combination of computational fluid dynamics(CFD)method and experimental measurement. The numerically predicted performance with the standard k-ε turbulence model showed good agreement with the experimental data, demonstrating CFD method can replace experimental approach in analysis of the flow field in the pump. Three radial clearances designed and the fluid tangential velocity distribution as well as pressure fluctuation in the two side chambers were compared. The results showed that the dimensionless tangential velocity in the front side chamber increases with reducing radius observed, and the fluid rotational angular velocity can exceed the impeller rotational angular speed, but the dimensionless tangential velocity decreases with reducing radius in the rear side chamber essentially. The pressure fluctuations in the radial gap and impeller exit are mainly with a frequency in the range of 0-1 680 Hz, but also the dominant pressure fluctuations occur at diffuser blade passing frequency. The amplitude of pressure fluctuations with the dominant frequency decreases progressively from the first stage to the last stage. The pressure fluctuation in the radial gap is also affected by the number of impeller blades. The secondary dominant pressure fluctuations appear at impeller blade passing frequency, and the pressure fluctuations also exist at the other multiplications of impeller blade passing frequency.
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