The internal flow patterns of a volute-type discharge passage were investigated in a mixed-flow pumping system based on CFD by using the RNG    turbulence model to close the time-averaged Navier-Stokes equations. According to the numerical analysis of the internal flow, the hydraulic characteristics of the volute-type discharge passage and the velocity distribution features in several key cross sections were analyzed and quantitatively calculated in terms of velocity distribution uniformity

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... nd bias angle. The computed results show that the internal flow field is very complicated involving flow separation and vortex in some regions and the velocity distribution is uneven. The uniformity curves of axial velocities in the outlet cross-section of the volute and the outlet cross-section of the passage are protruding ones while the bias angle curves in the same cross-sections are concave ones, both of them reaching their maximum or minimum value respectively at the flow rate corresponding to the best efficiency point of the pumping system. The hydraulic loss of the volute-type discharge passage varies with the discharge and reaches its minimum when the pumping system efficiency approaches its highest. When the pumping system operates under off-design condition on the large flow rate side, the hydraulic loss of the passage tends to increase rapidly causing the pumping system efficiency to drop sharply. Therefore, appropriate regulation methods should be adopted to adjust the pump operating condition to ensure the pumping system working within high efficiency zone.