Abstract: Due to the complex structure of the composite impeller, vortex structures such as tip leakage vortex and axial vortex will be generated in the impeller, which will seriously affect the internal flow field and the performance of fluid machinery. In order to reveal the influence of the number of blades on the hydraulic performance and internal flow field of the new open pump, the k-ε turbulence model was used to simulate four different blade number schemes with the same cascade density. The results show that the double tongue design of volute has effect on the flow field in the impeller channel, and the flow in the blade presents the law of alternating change. The inlet and outlet of the impeller are subject to high turbulence, while the vortex intensity at the central is relatively low. With the increase of the number of blades, the hydraulic performance of the composite blade increases, the pressure in the impeller decreases, but the vorticity increases obviously, and the strength of the vortex increases. The distribution of vortices at different sections is analyzed by Q-criterion, the results show that a number of vortex structures are generated on the suction surface of the impeller due to the interaction between the trailing edge vortex and the secondary flow. The leakage vortex in tip clearance develops from the back of blade to the middle of runner. With the development of flow, the range of vortices becomes larger and the shape of vortices also changes. In conclusion, the above results can provide reference for choosing blade numbers of the composite impeller.

Key words: blade number, composite impeller, Q-criterion, numerical simulation