Numerical Simulation of the Unsteady 3D Flow in Vertical Slot Fishway—The Impact of Macro-Roughness

Vertical slot fishways (VSFs) are crossing devices that are built on rivers or streams. They were initially designed to help salmons to complete their migratory cycle by crossing permanent obstructions. In order to favor the passage of smaller or benthic species, stones or concrete cylinders, called macro-roughnesses, are often inserted at the bottom of the fishway. To study the effects of macro-roughnesses on the flow inside a VSF, three-dimensional unsteady simulations were carried out using the volume of fluid method to model the free surface. In this paper, kinematic quantities obtained by CFD are used to detail the flow inside a VSF with and without macro-roughnesses. It can provide valuable information about the flow characteristics, especially in areas where the experimental measurements are difficult to implement.