Numerical modelling of the hydrodynamics and total dissolved gas downstream of Hells Canyon Dam

摘要

A computational fluid dynamics model was developed to predict the flow pattern and total dissolved gas (TDG) distribution downstream of Hells Canyon Dam on the border of Idaho and Oregon, USA. Free surface simulations in the tailrace were carried out to predict spillway jet regimes with and without deflectors. Model results agreed with deflector performance curves obtained in a 1:48 laboratory scale model. The distribution of TDG was predicted with a mixture model that accounts for the two-phase flow in the tailrace and the mass transfer between bubbles and water. Attenuation of the turbulence at the free-surface and the effect of the bubbles on the turbulence was included to capture water attraction towards spillway surface jets, which affects the amount of water exposed to bubbles and downstream TDG dilution. The model takes into account changes in bubble size with dissolution and pressure. Good agreement was obtained between predicted TDG and available measurements in the field.