Toward sustainable seawater pumped hydro storage: Mitigating strike-induced fish injury with a novel twisted blade

Ocean energy significantly expands the potential for seawater pumped hydro storage worldwide, as it is far less site-specific than traditional freshwater systems, which also requires measures to protect marine organisms from the threat of rotating blades. This study investigates mechanical-related fish injuries caused by blade strikes and proposes a high-efficiency twisted blade, characterized by a power function, to enhance fish friendliness. A coupled numerical simulation was conducted and experimentally validated to evaluate fish safety when passing through a tubular-flow pumping system. The results reveal that rotating blades cause the greatest damage compared to other flow components, and that a sharper leading edge with a larger slanted angle effectively reduces strike forces. Furthermore, the normal component of the strike force is the primary factor causing fish injury, and force reduction is achieved through a larger decrease in the normal direction and a smaller increase in the tangential direction. During a strike, changes in fish momentum normal to the contact surface are more damaging than momentum variations tangential to it, which typically result in non-fatal scale damage. The findings of this research provide comprehensive guidance for fish-friendly designs of turbomachinery, contributing to the sustainability of ocean energy utilization.