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The inlet flow conditions will directly affect impeller performance, which is of great concern to pump designers. In this study, based on two axial-flow pump devices, the influence of the evaluation criteria of inlet flow conditions and numerical grid scales on the accuracy of the simulation are investigated, the correctness of the numerical simulation are verified by experiments. The axial velocity distribution uniformity, axial velocity weighted average angle and hydraulic loss are calculated with three grid scales commonly used in engineering. The applicability of three turbulence models in engineering is verified. The influence of the uniformity of the axial velocity distribution on the impeller is quantitatively explored by installing a group of vortex generators. The results show that the simulation errors of the common formula of the axial velocity distribution uniformity for the elbow inlet passage and front-shaft tubular inlet passage are 16.3% and 14.6%, respectively; the modified formula limited the computational error to 0.2%, which reduced the axial velocity distribution uniformity dependence on the grid. The quantitative relationship between inlet flow conditions and pump performance was established, as the impeller efficiency decreased linearly with decreasing axial velocity distribution uniformity.

In order to explore the transient characteristics of the large-scale vertical siphon axial flow pumping station during the start-up and exhaust process, numerical simulations were carried out on the start-up process of the axial flow pumping station under the two starting modes of pre-opening the vacuum breaking valve and keeping the vacuum breaking valve closed. The calculation results show that during the start-up phase of the unit, the flow separation phenomenon of the impeller channel of the pump device with the vacuum breaking valve closed is serious, the large-scale vortex in the guide vane blocks the flow channel, and the instantaneous impact on the blade surface is strong. The flow field of the pump device with pre-open vacuum failure valve is obviously less affected by the instantaneous impact characteristics during the start-up of the pump. The range of high entropy production area in the impeller channel is reduced, the duration of high entropy production area is significantly shortened, and the instantaneous impact on the blade surface is weak. Under the two starting modes, the internal flow field of the pump device is similar in the evolutionary law. The unstable flow phenomenon of the pump device is most prominent in the weir flow stage. The maximum instantaneous impact on the blade surface also mainly occurs in the weir flow stage. A very small part of the remaining gas in the siphon formation stage is difficult to discharge and takes a long time. After the pump device is exhausted and enters a stable operation state, the external characteristic parameters are in good agreement with the test results. Compared with the starting method in which the vacuum breaking valve is kept closed, the method of pre-opening the vacuum breaking valve reduces the maximum starting head by 20% and the exhaust time by 43%. The pre-open vacuum breaking valve effectively avoids the system instability caused by the start-up and exhaust of the pump device.