Water hammers seriously endanger the stability and safety of pipeline transportation systems, and its protection mechanism has been a hotspot for research. In order to study the change of water hammer pressure caused by the ball valve under different closing laws, the computational fluid dynamics method was used to perform transient numerical simulation of the ball valve under different closing times and closing laws. The results show that the faster the valve closing speed in the early stage, the greater the water hammer pressure. The vortex core motion and pressure vibration were affected by the closing law. Extending the valve closing time can effectively reduce the maximum water hammer pressure. These findings could provide reference for water hammer protection during the closing process of the pipeline system with the ball valve.

Axial flow pumps, widely utilized in critical fields such as agricultural irrigation, urban water diversion and flood control, play an indispensable role in large-scale water transport and drainage projects due to their high-flow and low-head characteristics. This study systematically investigates the influence of tip clearance on the external characteristics and internal flow field of a large-scale axial flow pump (model 1800GZX-125). By combining numerical simulations with experimental validation, a comparative analysis was conducted under four tip clearance sizes (3 mm, 12 mm, 17.5 mm, 24 mm) and various flow conditions. The results indicate that increasing the tip clearance generally reduces the pump head and peak efficiency. It also alters the blade pressure distribution, expands the low-pressure region, and intensifies tip leakage flow. While vorticity overall increases, it weakens locally under certain conditions due to changes in leakage flow patterns. Entropy generation analysis further reveals that larger clearances lead to significantly increased energy losses, thereby degrading external performance. These findings provide a theoretical basis for improving the performance and operational stability of axial flow pumps.