Diagnosis of internal energy characteristics of mixed-flow pump within stall region based on entropy production analysis model

In order to investigate the influence of tip clearance size on the characteristics of mixed-flow pump under stall conditions, the entropy production analysis method is utilized to visualize the high energy loss area of main flow domains in internal flow fields. The results shown that the tip clearance size will not only affect the internal flow fields of mixed-flow pump under designed point but also play a remarkable role in the hydraulic loss with stall region. As the tip clearance increases from 0.2 mm to 1.1 mm, the head difference between critical stall condition and deep stall condition is about 0.79 m, 0.58 m, 0.52 m and 0.35 m, indicating that the intensity of tip leakage flow (TLF) is not linear with tip clearance size. The inflow instability at pump inlet will increase as the growth of tip clearance size, and it comes from the inlet swirling flow induced by the return of TLF. The high loss in impeller is caused by the TLF and stall vortex under stall conditions while the large-scale flow separation vortex and back flow from the annular volute are responsible for the high loss area in guide vane domain. The results could be referred to optimize the hydraulic structure of mixed-flow pump.