River diversions are often equipped with some device to exclude fish, such as fish screens. Flow pattern changes due to fish screen systems were investigated using a three-dimensional numerical model solving the Reynolds-averaged Navier-Stokes (RANS) equations. A porous media obstacle, which is commonly used for ground water flow modelling, was employed to model a fish screen. Fish screens require a velocity component perpendicular to the screen (approach velocity), allowing for water diversion. Meanwhile, it is imperative that this velocity not result in pinning fish to the screen but allowing for fish to be guided to a different location. Thus the ratio of sweeping velocity to approach velocity (V R ) is an important criterion in fish screen design. 20:1 V R and 10:1 V R models were tested under high and low flow rates in this study. Screen head loss coefficients for various wire Reynolds numbers were compared with laboratory model measurements to verify the mathematical results. Two different screen types were simulated: perforated plate and wedged wire. Altering global porosity and local permeability of a porous obstacle results in flow direction changes that effectively simulate different screen materials in the numerical model. Model simulations of head loss coefficients and velocity ratios showed good agreement with the laboratory model measurements. The wedged wire allows for more control of the velocity ratio along the screen system than the perforated plate. Baffles installed behind each fish screen bay promote uniform flow distribution along the screen. The porous media obstacle assumption is shown to effectively simulate the hydraulics of various configurations of fish screens at river diversion channels.

A numerical modeling study of hydraulic performances of an angled vertical fish screen at a river diversion intake channel that was developed using a porous media numerical scheme. Flow patterns in the intake channel induced by the fish screen were computed with a three-dimensional fluid dynamics computation program solving the Reynolds-averaged Navier-Stokes equations. Screen flow head loss coefficient were simulated and compared with the physical model values converted from the test measurements for the porous media numerical scheme applicability test. For validation of the numerical model, fish screen velocity ratio profiles of sweeping and approach were compared with physical model measurements. Different types of screen face material and baffle installations for uniform approach flow distributions were simulated. The numerical model shows very good agreement with the velocity ratio measurements, and modeling capability for different screen material types and baffle installations by controlling of the numerical model of the porous opening directions and adjustment of baffle porosities respectively.