Abstract: In order to study the stall in centrifugal pumps, the internal flow field in three sections of a doubleblade centrifugal pump was measured by 3D particle image velocimetry technique (PIV) at four flow rates. With the decrease of the flow rate, flow separation occurs at the pressure side of the impeller blade firstly, which results in a vortex near the pressure side of the blade. When the flow decreases more, the vortex blocks the channel and flow field gets worse, which causes the stall phenomenon. Under the optimum condition, the flow pattern in the impeller is best. At 0.8Qopt (the flow rate at the optimum condition), flow separation is observed in the middle section. At 0.5Qopt, the stall occurs in the middle section due to the extending of flow separation. Before reducing the flow rate to 0.2Qopt, the stall occurs in the section near the shroud. But there is no vortex found in the section near the hub. The axial velocity field in the passage shows an asymmetrical distribution, and the axial velocity decreases from the entrance to the exit of the passage. Also, it decreases from suction side to pressure side of the blade. And the negative axial velocity area near the pressure surface extends with the development of stall.

Key words: double-blade centrifugal pump, stall, 3D particle image velocimetry technique (PIV), flow separation, vortex