In this study, the numerical investigation on the interaction between the volume and the diffuser with different outlet angles in the nuclear main pump was conducted by using the commercial software NUMECA. It was found that the static pressure increases gradually from the diffuser outlet to the volume wall with the maximum value presenting near the volume wall. The back flow at the volume outlet results in a significant flow loss, which is the main reason for the low efficiency of the nuclear main pump. Moreover, the pump head and efficiency increases with decreasing the outlet installation angle of the diffuser. However, it is important to be noticed that the growth rate become increasingly small with a little decrease of the pump head when increasing the outlet angle to 20ð , which means 20ð should be the optimal angle for installing the diffuser outlet.
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