Investigation of vortex dynamics diagnosis in the stall state of mixed-flow pump with blade gap size effect

Rotating stall always occurs in the mixed-flow pump operating at partial load condition, not merely affecting the unit efficiency, but also generating more serious turbulent flow fields. The tip leakage vortex (TLV), as a classic vortex structure in hydraulic machinery, is deserved to investigate the impact on the energy conversion instability of mixed-flow pumps. In this study, the blade tip size effect has been considered and the stall transition flow fields are investigated in detail based on the vortex dynamics diagnosis (VDD) method. The research results show that the blade tip size plays a pivotal role in the stall range of mixed-flow pump, and display a shrinking tendency with size growth. The negative value of total pressure flow integral (TPFI) P u comes up with the inlet recirculation vortex and the large-scale stall vortex affected by the stall unsteady flow, which stands at the impeller inlet and outlet. The P u and stall flow in the guide vane channel are also affected indirectly by the impeller gap size, not just the stall flow in the impeller. Thus, the selection and control of impeller gap size will provide a light perspective for the pump optimization and stall control in the mixed-flow pump.