A numerical approach for active fish behaviour modelling with a view toward hydropower plant assessment

A numerical approach for assessing the injury risk of fish during turbine passages is introduced. The approach combines computational fluid dynamics (CFD) coupled with the discrete element method (DEM), and extends it with fish behaviour models. The fish behaviour is achieved by an additional force term acting on the particles. Based on ethohydraulic observations three rules of conduct were defined and combined via weighting factors. These rules represent 1) the aim to follow the main flow direction, 2) the instinct of downstream migration, and 3) an avoidance reaction towards moving objects. It is shown that the behavior of the fish surrogates can be actively tuned and adapted. This allows for the expression of both individual and collective behavior with the implementation of instantaneous reactions to the local, unsteady flow conditions in a trade-off with global behavior rules. Therefore, the approach allows for the investigation of a large bandwidth of tasks related to etho- and ecohydraulics and is not limited to the case at hand. In this study, the model is deployed on an example case of a water vortex power plant (WVPP) that allows for the presentation of the general mechanisms and advantages of the method.