Locomotion and strike damage of fish passing through a fish friendly tubular pump using computational fluid dynamics and discrete element coupling method

The tubular pump is a typical water transfer apparatus designed for extremely low heads and large flow rates. It serves as the core equipment in pumping stations situated at lakes, rivers, and canals. An adverse effect on the ecological environment stems from fish injury and mortality primarily caused by blade strikes. The present work combines computational fluid dynamics and the discrete element method to simulate the dynamics of fish passing through a simplified blade, allowing us to establish a safe margin of the strike force to further assess fish damage in a more complex tubular pump system. The results indicated that strikes on fish alter their motion state in terms of direction and magnitude, inducing chaotic movements that heighten the risk of subsequent strikes with downstream components. Fish tend to align their velocities with the surrounding fluid due to flow-induced drag after multiple contacts with solid structures. The knife-shaped leading edge, and particularly the blade tip side, emerged as the primary factor in creating strike damage, and the adoption of a slanted and blunt leading edge can effectively reduce fish damage. In addition, decreasing the shaft speed, increasing the flow rate, and restricting the fish size were identified as measures conducive to fish survival in running pumps. The study further suggested that using fewer but larger pumps operating at lower shaft speeds would contribute to better fish friendliness, which can also ensure a sufficient delivery head and mass flow rate.