A vertical mixed-flow pump characterized as large flowrate and high efficiency is used for water supply in the power plants and seawater desalination plants. High specific speed pumps, like axial and mixed-flow pumps, tend to present saddled formation “dip” which restricts the operation range of the pumps due to vibration and noise.

In this study, the pump performance test was performed to compare with the numerically simulated results for the mixed-flow pump with specific speed of 780 (m3/min, m, rpm). The impeller tip clearance effect on the pump head and hydraulic efficiency was investigated. The numerically simulated results showed that tip clearance effect changes Q-H curve. It is deduced that altered flow field of outer streamline is related with the prediction of dip phenomenon. Also, possible causes of dip were investigated and a new pump having Q-H curve free from saddled formation was designed.

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