Experimental Investigation on Diffuser Rotating Stall in a Three-Stage Centrifugal Pump

Abstract

Rotating stall phenomenon frequently causes the troubles such as vibrations acting on the shaft system and reduces the reliability of turbomachines. In the present study, the diffuser rotating stall in a three-stage centrifugal pump was experimentally studied. Special emphasises were placed on the geometrical conditions; an axial offset of rotor against the stationary part, which might be unavoidable due to accumulation of geometrical tolerances and assembling errors., and the radial clearances of annular leakage paths which increases the thru-flow rate at the impellers and the first and second stage diffusers. As a result, with the rotor axial offset to the suction side, the rotating stall appeared only at the third stage diffuser, while with that to the discharge side, the rotating stall was more significant. By enlarging the leakage flow passages at the inter-stage bush and the balancing flow channel, the onset range of rotating stall became narrower in the first and second stage diffusers, which was well explained by the increase of the thru-flow rate. On the other hand, with the enlarged leakage passage at the liner ring, the onset range became slightly wider.

Numerical investigation of radial thrust fluctuation caused by diffuser rotating stall in a centrifugal pump

“…Subsequently, the effect of axial offset of the whole rotor system was tested, and it was found that the rotating stall tends to be suppressed when the axial rotor offset is given toward the suction side [4]. Besides, the effects of enlargement of gaps at annular seals were also investigated, and it was found that the gap at the liner ring, which governs the leakage flow at the front side of impeller, especially has a remarkable effect on the rotating stall [5]; the rotating stall becomes to occur also in the first and second stages after enlarging the gap at the liner ring.…”