Low flowrate effects in a centrifugal pump impeller

This paper reports on an experiment in a centrifugal pump at low flowrates. A variety of measurement techniques was used: laser Doppler anemometry (LDA), impeller vane surface static pressure, a three-hole pneumatic probe and time-resolved static pressure. Some light is shed on the flow mechanisms present in the impeller off design. Evidence is found of a recirculation vortex, at 49 per cent of design flow-rate, in the impeller flow passages. From design flowrate down to 46 per cent of design flowrate there is no evidence of rotating stall, which first appears at 43 per cent. The most likely interpretation of this result is that there is a three-cell rotating stall system with the cells rotating at approximately 43 per cent of the impeller rotational speed. At 20 per cent of the design flowrate, the fluid in the inlet pipe ‘prerotates’ with no time mean flow reversal, interpreted as a developed stall cell system.