Author(s): Aurelien Ballu, Gerard Pineau, Damien Calluaud, Laurent David
Linked Author(s): Laurent David
Keywords: Vertical slot fishway, numerical simulation, URANS, LES, macro-roughnesses
Abstract: The European Water Framework Directive aims to restore the ecological continuity of European rivers and streams and more specifically the free circulation of aquatic species. To fulfill those requirements, vertical slot fishways (VSF) are built to provide the possibility for fish to cross dams or weirs. Initially, such devices have veen constructed to allow the migration of fish species with an important swimming capacity like salmonids. Currently, more and more VSFs are equipped with macro-roughnesses fixed on their bed to help small or benthic species to cross obstructions. Macro-roughnesses are most often stones or concrete cylinders. To study the effects of such macro-roughnesses on the pool flows, unsteady 3D flow simulations are carried out. This paper presents the results of 3D URANS and LES studies of a VSF with and without equally spaced cylinder-shape macro-roughnesses. The volume of fluid method is used to simulate the free surface and the interaction between the two phases (water and air). Results show that both URANS and LES models are in good agreement with experimental velocity profiles. However, the turbulent kinetic energy is quite under-estimated when using the URANS model. Finally, the LES method is used to characterize the effect of macro-roughnesses on the flow. It is shown that the zone in the vicinity of the macro-roughnesses gives potentially more favorable flow condition for benthic species. The present study demonstrates that LES calculation can give a useful modelling of the flow existing inside a VSF with macro-roughnesses. It can provide valuable information of the flow characteristics, especially in areas where the experimental measurements are complicated to implement
Year: 2017