The formation of an inlet vortex seriously restricts axial-flow pump device performance and poses a great threat to the safe and stable operation of the entire system. In this study, the change trends of an inlet vortex and its influence on an axial-flow pump are investigated numerically and experimentally in a vertical axial-flow pump device. Four groups of fixed vortex generators (VGs) are installed in front of the impeller to create stable vortices at the impeller inlet. The vortex influence on the performance of pump device is qualitatively and quantitatively analyzed. The vortex patterns at different positions and moments in the pump device are explored to reveal the vortex shape change trend in the impeller and the pressure fluctuation induced by the vortex. The reliability and accuracy of steady and unsteady numerical results are verified by external characteristics and pressure fluctuation experimental results. Results show that it is feasible to install VGs before the impeller inlet to generate stable vortices. The vortex disturbs the inlet flow fields of the impeller, resulting in significant reductions of the axial velocity weighted average angle and the axial velocity uniformity. The vortex increases the inlet passage hydraulic loss and reduces the impeller efficiency, while it only slightly affects the guide vane and outlet passage performance. The vortex causes a low-frequency pressure pulsation and interacts with the impeller. The closer the vortex is to the impeller inlet, the more significant the impeller influence on the vortex. The blade cuts off the vortex in the impeller; afterwards, the vortex follows the blade rotation, and its strength weakens.

To study the significance of internal pressure pulsation characteristics between prototype and model pump devices, monitoring of computational fluid dynamics and dynamic measurement of a model were carried out under different working conditions and measuring points. The results of computational fluid dynamics calculation and model test are as follows. First, the positions of main frequency and subfrequency are almost the same, whereas the amplitude has a slight deviation. Second, the amplitude of inlet impeller is larger, and the main frequency is three times of rotating frequency. Third, the inlet speaker has mainly low pulsation, which is almost distributed in blade frequency and 1/3 times of rotating frequency. Moreover, the pressure pulsation of symmetrical points in each condition has a good symmetry. As the flow rate decreases, both the mixing and blade frequency amplitudes in the inlet speaker and impeller first decrease and then increase. The minimum mixing amplitude appears in the design condition of 253 L/s, whereas the blade frequencies are 203 and 253 L/s. The numerical calculation results are almost the same as those of prototype and model devices. Therefore, numerical calculations and experimental studies on pressure pulsation can guide the design and stable operation of similar pump stations.

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.