Numeriska simuleringar av vertikala slotfiskvägar: Hydrodynamisk jämförelse av ett öppet och ett stängt system

A Vertical Slot Fishway (VSF) is a common technical fish pass to allow for upstream migration past barriers and dams associated with hydropower plants. The reinstatement of river connectivity can improve biodiversity, increase fish populations, and prevent deterioration of aquatic habitats. Passage efficiency in a VSF depends on both fish swimming behavior and the hydraulic design of the fishway. To maintain suitable hydrodynamic conditions for fish in terms of turbulence and velocity, the slope of the floor needs to be relatively low, approximately 5%. However, for high-head dams and barriers, this design constraint leads to costly and large constructions. Constructing the VSF as a closed system by adding a lid to eliminate the free surface could change the hydrodynamics within the pass, potentially mitigating the design constraint. This thesis investigates the hydrodynamics of a closed VSF by solving the incompressible, Newtonian Navier-Stokes equations in the software OpenFOAM, using the finite volume method and the volume of fluid to model the free surface. A model validation case was conducted by implementing three numerical models in OpenFOAM: the SST k − ω RANS model, k-equation LES model, and the SST k − ω IDDES model. Simulated results were compared to experimental data collected from a prototype of an open and closed system at Vattenfall R&D Älvkarleby. The best-performing model was then used to analyze and compare the hydrodynamic conditions betweenthe open and the closed system, this to be able to link fish behavior to turbulent characteristics. It was found that the LES model best replicated the physical system, whereas RANS and IDDES failed to capture the flow pattern present in the open system. Further, the flow analysis showed that the closed system had a higher velocity in the slot and smaller turbulent structures when compared to the open system. In the open system, fish might struggle with turbulent structures, while in the closed system, there might be a velocity barrier. Further research is needed to explore alternative configurations of the closed system to investigate the hydrodynamics and suitability for fish.