Computational fluid dynamics modeling of turbine intake hydraulics at a hydropower plant

The U.S. Army Corps of Engineers (USACE), Portland District is considering blocking the upper 12.3m of the turbine intakes at The Dalles Dam, Oregon with a J-shaped blocked trashrack (a steel panel in front of the existing trashrack). The objective is to create a forebay flow pattern aiding the downstream migration of juvenile fish. A three-dimensional (3D) computational fluid dynamics (CFD) model of a turbine unit of the dam has been developed to investigate the impact of the proposed blocked trashrack on the turbine intake hydraulics. The model was verified by comparing velocity distributions in a 1 : 25 scale physical model by Engineering Research and Development Center (ERDC), Vicksburg, Mississippi. Numerical simulations indicate that the blocked trashrack creates a relatively quiescent, near dead flow zone above it. Below the trashrack, flow is more horizontal into the turbine intakes. However, velocity distributions inside the intakes are significantly more non-uniform. Near-dead flow zones are created in regions immediately behind the blocked trashrack. Cross-sectional velocity distributions show strong eddies in the intake. The analysis suggests the need for investigating improved turbine intake design when retrofitting existing dams with juvenile fish bypass facilities.