Lagrangian validation of CFD models assessing risk for fish injury

Abstract: Engineered conveyance structures on rivers disrupt fish movements. Understanding of fish injury risk when transported across these structures is limited, including transport through closed conduit systems. Herein, this research aims to provide missing information on hydrodynamic stressors in pipes and pipe components that fish can be transported through without injury. Lagrangian sensors were used in a physical model, systematically measuring accelerations and pressures in various pipe components. This was complemented with live fish testing, establishing injury thresholds in closed conduit systems and documenting fish movements when travelling through pipe components. A CFD model of the laboratory experiments was developed and the Lagrangian pressure and acceleration data were used for validation. An inert Discrete Phase Model (DPM) was used to represent the Lagrangian motions and the sensitivity of particle diameter, density and shape factor was assessed. Results showed that massless particles provided better pressure estimates while inert particles matched the overall travel times. Shape factor had the largest effect on DPM outputs. No method fully matched the fish pathways through the pipe system, highlighting a need for future research to incorporate active fish movement in the models. Keywords: Closed conduit flows, Lagrangian sensors, Australian fish, CFD particle tracking, fish passage