Computation Of The Free Surface Flow In A Fish Passage

Abstract

A numerical study of the free surface flow on an ogee-crested fish bypass is presented. The geometry corresponds to a juvenile fish bypass proposed for Wanapum Dam, on the Columbia River, State of Washington. A free-surface numerical model which solves the RANS equations coupled to a surface-capturing algorithm to predict the flow in air and water was developed using the volume of fluid (VOF) method with the commercial CFD code Fluent 6.1. The k epsilon-µ model of turbulence with wall functions was used to compute the eddy viscosity. Structured/unstructured hybrid grids were used to accommodate the complex geometry that included gate slots, flow control gates, and an aeration slot. The tailrace performance curves were reproduced numerically, predicting the plunging, skimming or surface ramp regimes resulting from different tailrace elevations. Free surface elevations, pressure along the ogee surface, and discharge rating curves were compared against the experimental data from the laboratory model for different headwater elevations and gate settings. Once deemed reliable through validation against experimental data, the computational model was used to analyze the flow field, supplementing the areas of limited experimental data. Predicted numerical model results included pressure and velocity distributions and free-surface configurations that helped analyze cavitation potential and flow performance of the spillway. Future analysis may link the hydrodynamic results with an existing fish behavioral model