Abstract
The flow instability in a low specific speed mixed-flow pump, having a positive slope of head characteristic curve was investigated. After it was found from pressure measurement that a rotating stall in the vaned diffuser caused the instability, dynamic Particle Image Velocimetry (PIV) measurement and numerical simulation of Computational Fluid Dynamics (CFD) were carried out. Then, the rotating stall is simulated even in CFD and calculated patterns of instantaneous velocities agree well with measured ones by dynamic PIV. It is indicated that a periodical large scaled backflow, generated at the leading edge of the suction surface of the diffuser vane, causes the instability. Moreover, the growth of the strong vortex towards the leading edge of diffuser vane induces the strong backflow from the diffuser outlet to the inlet. The scale of one stall cell is covered over four-passages in thirteen vane-passages.
