This article explores the impact of inlet pre-swirl on pressure pulsation in a mixed-flow centrifugal pump through a combination of numerical simulations and experimental verification. Firstly, the mixed-flow centrifugal pump’s performance was initially determined through both numerical calculations and experiments. The comparison between them indicated the high accuracy of the numerical method adopted in this paper. Next, the flow pattern within the pump at various inlet pre-swirl angles was carefully compared and analyzed. It was found that positive impulse angle and inlet displacement could lead to circumferential inhomogeneity of the flow field within the impeller, while inlet pre-swirl can significantly counteract the effect of positive impulse angle. The impact of inlet pre-swirl on the flow pattern near the blade inlet will change the intensity of the secondary flow within the impeller passage. Variations in the intensity of the secondary flow can directly affect the strength of the wake and jet in the chamber. Then, the pressure pulsations within the chamber were compared and analyzed for various inlet pre-swirl angles. The results revealed that as the inlet pre-swirl angle increased, the intensity of pressure pulsation decreased significantly. This discovery sheds light on the influence mechanism of inlet pre-swirl on pressure pulsation within mixed-flow pumps, potentially serving as a theoretical foundation for enhancing the operational stability of mixed-flow centrifugal pumps.

The lower Yellow River is characterized by low water discharge and a high sediment load, resulting in a fragile aquatic ecosystem. It is important to develop a reasonable method of ecological flow calculation that can be applied to the water-scarce rivers like the Yellow River. In this paper, we selected the Huayuankou hydrological station in the lower Yellow River as our study site and assessed the ecological flow using several methodologies including the monthly frequency calculation method, the sediment transportation method, the habitat simulation method, and the improved annual distribution method. Based on the seasonal applicability of the four methods across months of the year, we established an ecological flow calculation method that considers the integrated ecological functions of the lower Yellow River. In this method, ecological flow in the lower Yellow River during the dry season (November to March) can be determined by using the improved annual distribution method, ecological flow in the fish spawning period (April to June) can be calculated using the habitat simulation method, and the ecological flow during the flood season (July to October) can be calculated using the sediment transportation method. The optimal ecological flow regime for the Huayuankou section was determined using the established method. The ecological flow regimes derived in our study ranged from 310 m³/s to 1532 m³/s. However, we also observed that the ecological flow has a relatively low assurance rate during the flood season in the lower Yellow River, with the assurance rate not exceeding 63%. This highlights the fact that more attention should be given in reservoir regulations to facilitating sediment transport downstream.