Abstract: In order to explore the effect of tip clearance on the external characteristics and cavitation performance of the axial flow pump, based on the modified SST k-ω turbulence model and Z-G-B cavitation model, the numerical simulation of the 350ZQ-70 submersible axial flow pump in different tip clearance was carried out to compare and analyze the external characteristic, the pressure pulsation and the distribution of cavitation volume fraction in the impeller passage. The results show that the pump head and efficiency decrease with the increase of the tip clearance, the flow instability phenomenon is obviously strengthened under the condition of small flow, and the hump phenomenon appears in the head curve. Cavitation of inlet edge is more likely to occur near the hub than near the shroud. At the design flow rate, cavitation of tip clearance first appears in the middle of the blade, not at the blade inlet. The cavitation at the back of the blade will affect the pressure distribution on the working face of adjacent blades. There is a critical value of clearance, before this value, the increase of the tip clearance mainly reduces work capacity of the impeller, and has little effect on cavitation performance; beyond this value, the stability of the leakage vortex decreases and the pressure pulsation increases. For the test pump, the critical value is between 1.5~2 mm; The degree of cavitation of inlet is reduced with the increase of clearance; According to the assembly structure of axial flow pump impeller, in the light of protecting the impeller body, considering the work capacity and operation stability, it is more appropriate to select a clearance of 1.5 mm for the test pump.

Key words: axial flow pump, unsteady numerical simulation, cavitation flow, tip clearance