Vortex identification based on the Liutex method and its effect on fish passage upstream

Fishway research is important for mitigating the fragmentation of river habitats caused by hydraulic projects. The vertical slit fishway is a broadly used fishway type because of its high efficiency and adaptability to water levels. However, the resulting vortex current disrupts the fish passage hence directly affecting fish migration. This study aims to accurately capture the vortex structure in the fishway and analyze the effect of vortex elements (vortex structure, vortex intensity, etc.) on fish. We conducted an analysis of the 3-D current flow field in the fishway through the utilization of an experimental model and the large eddy simulation (LES) method. Moreover, we captured the vortex information in the fishway at different flow rates using the Liutex vortex identification method and investigated the effect of the vortex on fish migration. The results revealed that the structures inside the fishway pool occupy most of the room, however, the areas with higher vortex strength were primarily located in the vortex near the vertical seam and the mainstream, the vortex strength inside the fishway gradually increases with increasing flow, suppressing fish migration. Fish experienced significantly increased resistance when encountering strong vortices. This suggests that the vortex may act as a physical barrier to fish migration. These findings highlight the potential negative effects of vortex on fish movement and reiterate the importance of understanding vortex dynamics for aquatic environmental management. As an effective tool for identifying vortices in fluid flow, the Liutex method demonstrates features of vortex within the fishway, thereby providing important insights into the interaction between fluid dynamics and aquatic organisms.