A Comprehensive CFD Model for Spillway Deflector Design at Hells Canyon Dam

摘要

Elevated total dissolved gas (TDG) can cause gas bubble disease in migrating fish. The main source of elevated TDG in a dam is the dissolution of air from bubbles entrained during spill events at depth. In order to prevent bubbles plunging to depth in the stilling basin of Hells Canyon Dam, spillway deflectors were designed using a 1:48 scale laboratory model. The deflectors were evaluated based on their capability to generate surface jets for a wide range of spill operations and tailwater elevations. In this study, a CFD model is developed to analyze the performance of different deflector designs considering not only TDG reduction but also changes in the tailrace hydrodynamics and possible mechanical injury to fish. The model predicts the hydrodynamics and TDG distribution at the dam and seven miles downstream. The two-phase flow in the stilling basin is simulated with a mixture model accounting for the mass transfer between bubbles and water, responsible for TDG production. The model is calibrated and validated using TDG field data. A particle tracking technique is used to evaluate possible fish injury. Deflector induced injury is analyzed by assessing accelerations and strain rate. Spillway jet regimes, propagation of surface waves, TDG production and fish possible mechanical injury for different deflector designs are presented and discussed.