Computational model of total dissolved gas downstream of a spillway

A predictive three-dimensional numerical model is developed for calculating total dissolved gas (TDG) production and transport downstream of hydropower dams. The model uses an existing Reynolds-averaged Navier-Stokes solver with k-ϵ turbulent closure for flow hydrodynamic simulation, while various TDG production and transport physics are incorporated in a separate model. The TDG model consists of three important model parameters: the TDG source strength parameter, free-surface transfer parameter, and turbulent Schmidt number. These three parameters are related to different physical processes and the determination of their appropriate values constitutes the major calibration procedure performed in this study. The TDG model parameters are calibrated against field data for a two-dimensional simulation, and are then validated by simulating the entire three-dimensional hydrodynamic flow field for multiple operational conditions.; A comprehensive literature review is presented to support the model development, revealing and combining the recent advances in three distinct research fields: computational fluid dynamics, air-bubble entrainment and total dissolved-gas production in spillway stilling basins. The application of the model to Wanapum Dam exemplifies the general methods that are applicable to other dams. The model reproduces the important TDG transport characteristics obtained from field programs as well as hydraulic model studies. Three-dimensional simulations are also performed with and without spillway deflectors to demonstrate the potential improvement of TDG levels after the installation of spillway deflectors.; This study provides the first three-dimensional numerical model for predicting TDG production and transport. The model can assist in analyzing geometric and operational alternatives for reducing TDG at hydropower dams. Such a model is useful for design engineers and decision makers, and ultimately will reduce the timeframes and costs of design and modeling.