Rotating stall mechanism and stability control in the pump flows

Based on experimental measurements and flow dynamics analysis, the mechanism of flow separations in the pump flow has been investigated and revealed. The possible flow separation including the rotating stall in the vaned diffuser under the normal flow condition has been confirmed to be merely a diffuser effect and caused by the oversized expansion angle of the diffuser. The dynamics of the part load flow separation of both the stationary and the non-stationary character has been identified to be related to the induced flow circulation at the impeller inlet. The associated flow separation mechanism has been revealed with respect to the build-up of a flow dynamical barrier on the shroud side of the impeller. It exactly explains the coincidence of the flow separation at the impeller inlet and that at the impeller outlet. To quantify the onset of the flow separation, a hypothesis is established based on the revealed mechanism. This has been satisfactorily validated by tests with flow visualizations, pressure measurements and laser doppler anemometry applications. The method for stability control of the pump flows with effective suppression of the flow separation has also been presented.