The steady flow in a low specific speed constant-head pump is simulated numerically by using ANSYS CFX software with the RNG k-ε turbulence model at five flow rates:0.6Qd, 0.8Qd, 1.0Qd, 1.2Qd and 1.4Qd. The static pressure and velocity fields on the mid-span surface of the impeller at flow rates:0.6Qd, 1.0Qd and 1.4Qd are investigated and the blade loading on the mid-span surface are analyzed as well. The normalized helicity Hn is used to analyze the flow conditions on the mid-span surface of the impeller and in the eight sections of the volute. The results show that an obvious backflow can be seen at the impeller outlet, and the angle of backflow tends to get small with the increasing flow rate. The blade shape has a certain influence on the blade loading distribution. The forward direction vortexes exist in the impeller passages, while a pair of symmetrical vortexes always occurs in the volute sections. This pair of vortexes experiences a stable, unstable and stable again development process when the fluid particles flow to the eighth section from the cut-water of the volute.
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