Influence of rotating speed on tip leakage vortex in a mixed flow pump as turbine at pump mode

Abstract

Tip clearance results in tip leakage flow from blade pressure side to suction side, and further deteriorates the energy performance and operation stability. In the present work, the influence of rotating speed on tip leakage vortex in a mixed flow pump as turbine at pump mode is investigated. As rotating speed increases, the pump head increases according to the similarity law and the best efficiency point shifts towards large flow rate. Meanwhile, the tip leakage flow and axial momentum also increase. A prediction model for separation angle of tip leakage vortex is proposed, and its relative error is below 5%. As rotating speed increases, the oscillating frequency of primary tip leakage vortex increases from 201.92 Hz to 215.60Hz, and the high pressure fluctuation region develops from leading edge to nearly the whole blade-to-blade passage.