The axial-flow pump system has been widely applied to coastal drainage pump stations, but the hydraulic performance optimization based on the contraction angles of the inlet passage has not been studied. This paper combined the computational fluid dynamics (CFD) method, machine learning (ML) algorithms and genetic algorithm (GA) to find the optimal contraction angles of the inlet passage. The 125 sets of comprehensive objective function were obtained by the CFD method. Three contraction angles and comprehensive objective function values were regressed by three ML algorithms. After hyperparameter optimization, the Gaussian process regression (GPR) model had the highest R² = 0.958 in the test set and had the strongest generalization ability among the three models. The impact degree of the three contraction angles on the objective function of the GPR model was investigated by the Sobol sensitivity analysis method; the results indicated that the order of impact degree from high to low was ${\theta }_3>{\theta }_2>{\theta }_1$. The optimal objective function values of the GPR model and corresponding contraction angles were searched through GA; the maximum objective function value was 0.963 and corresponding contraction angles were ${\theta }_1=13.34°$, ${\theta }_2=28.36°$ and ${\theta }_3=3.64°$, respectively. The results of this study can provide reference for the optimization of inlet passages in coastal drainage pump systems.

This study aimed to reveal the energy loss characteristics of each part of the shaft tubular pump device (STPD) under stall conditions. Numerical simulations were conducted by using the SST k-ω turbulence model with curvature correction, and the reliability of the simulation results was verified by a model test. The entropy production method was used to evaluate and visualize the energy loss. The results show that turbulent entropy production (TEP) is the main source of energy loss in each component of the STPD, and the TEP increases significantly with the deterioration of stall. The energy loss in the impeller is mainly concentrated near the shroud and hub, while in the guide vanes it is mainly concentrated near the shroud and suction surface of the blades. In addition, with the deterioration of stall, the energy loss in the inlet of the impeller and guide vanes increases significantly. Influenced by the backflow from the impeller, there is a significant amount of energy loss at the outlet segment of the inlet passage, and the location of the high-energy-loss region is consistent with the backflow region. Affected by the flow separation vortex at the tail of the guide vanes, the energy loss in the outlet passage is mainly concentrated at the inlet segment.

A slanted axial-flow pump is extensively applied in coastal pumping stations; however, severe bias flow within the outlet passage will result in unstable operation and low efficiency of the slanted axial flow pump system. In order to mitigate bias flow in a slanted axial-flow pump outlet passage, seven exit setting angle schemes of the guide vanes were designed. The influence mechanisms of the guide vane exit setting angle on internal flow characteristics, hydraulic loss, flow deviation coefficient, vortex evolution patterns, and pump system efficiency were systematically investigated. The results demonstrate that under design flow conditions, as the exit setting angle of the guide vane ranges from 90° to 105°, the flow field in the first half of the guide vane remains essentially the same. The low-velocity region at the guide vane outlet demonstrates initial contraction followed by gradual expansion with increasing stagger angles. Looking downstream within the flow passage from the left to the right, the hydraulic loss in the outlet passage goes up after an initial descending trend as the exit setting angle increases. When the exit setting angle is 97.5°, the bias coefficient of the outlet passage is 1.031. At this point, the vortex core distribution intensity within the outlet passage reaches a minimum, corresponding to the lowest recorded hydraulic loss of 0.230 m. Compared with the original guide vane scheme, the scheme with an angle set at 97.5° can improve the pump system efficiency of the slanted axial flow pump system, whether the flow is set at a design point or at a large point, and the pump system efficiency is increased by 2.3% under design flow conditions.

The rotation speed of water at the inlet of the low hump outlet conduit has a great effect on its hydraulic performance. Therefore, the influence of different inlet water rotation speeds on hydraulic loss and flow pattern of low hump outlet conduit is studied in this paper. By solving RANS equations and the RNG k-ε turbulence model, the hydraulic loss and 3D flow field of the low hump outlet conduit were calculated under different inlet water rotation speeds. To verify the numerical results, the model tests of low hump outlet conduit with different guide vanes were conducted. The results show that along with the growth of inlet water rotation speed, the hydraulic loss of outlet conduit will firstly decrease by degrees and then increase dramatically, the vortex location moves from the whole bottom of the descent segment to the right bottom of descent segment and the vortex area becomes smaller, the flow pattern of the whole conduit is improved obviously. The hydraulic loss and flow field of numerical simulation are consistent with those of the model test. Because of its great influence on hydraulic performance, inlet water rotation speed must be taken into consideration in the hydraulic optimization design of guide vane and low hump outlet conduit.

In multi-unit rural irrigation and drainage pump stations, unstable intake flow in side pump sumps often leads to vortex formation, jeopardizing safe operation. Therefore, this study investigates the influence of frictional hysteresis effects on flow patterns in the side pump sump of multi-unit rural irrigation and drainage pump stations through physical model experiments and theoretical analysis. Here, frictional hysteresis refers to the delayed and asymmetric development of wall-induced friction gradients along the sidewall and separating pier, resulting from different boundary-layer growth histories under asymmetric geometric constraints, which leads to persistent lateral momentum imbalance and biased inflow in the sump. The research reveals that due to structural asymmetry (the coexistence of a single-sidewall and a separating pier), frictional gradient deviation in side pump sump exhibits significantly non-uniform distribution along the flow direction. Specifically, the frictional gradient offset near the separating pier is greater than that near the sidewall and decreases along the flow direction while remaining relatively stable. By introducing the concept of the relative offset of inflow frictional gradient, the proportion of gradient offset to pump sump width was quantified. Experimental results show that when the width-to-length ratio is optimized to the range of 0.22–0.28. This significantly promotes a more laterally symmetric velocity distribution and effectively suppresses the formation of wall-attached vortices in side pump sumps. The findings provide a theoretical basis for optimizing rural irrigation and drainage pump station's intake structures, and it is recommended to control width-to-length ratio to reduce frictional hysteresis effects, thereby enhancing operational efficiency and stability.