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Pumps Assist Migrating Salmon on the Columbia River

 

Courtesy of ITT Flygt

The Columbia and Snake Rivers in the Pacific Northwest of the U.S. are home to about twenty hydroelectric dams. While these provide inexpensive power to the local communities, they also pose a threat to migrating fish, particularly the Pacific salmon. Early in their life cycle, the salmon migrate downstream to the sea. After maturing and spending two or three years in the ocean, the fish return to their birth-place to spawn. While the challenge of upstream migration of mature salmon past dams has been addressed with moderate success through fish ladders for the better part of a century, ensuring the safe down-stream migration of juvenile salmon remains a difficult task. Some estimates indicate that when the finger-sized fish swim through the hydroturbines, there is a mortality rate of up to 10% at each dam, resulting from the sudden pressure drop at the runner. In an effort to help channel juvenile fish through a safer bypass route around the dam, a unique 10 x 3 pump array is currently under construction. The ultra low head, low noise, submersible propeller pumps to be used were created specifically for this purpose by engineers at ITT Flygt of Stockholm, Sweden and Trumbull, CT, USA. The pumps will be used to draw water through a fish attraction channel and recirculate it into the headwater above the dam.

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A section of the array of Flygt's P7900 ultra low head pumps

FLUENT has been used for two facets of the project. First, it was used in the design phase to optimize the geometry of pump components such as the inlet, propeller, guide vane, and exit diffuser. Beginning in 1998, designs were tested using CFD and compared to data from a 1/6 scale model in the Flygt hydraulics lab in Stockholm.

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A wall vortex generated by a single pump in the full size prototype test rig in Pewaukee, Wisconsin

Second, FLUENT has been used in the application phase to understand better the inlet and discharge flows as well as the interaction between neighboring pumps in the array. The first CFD analyses on the discharge from a single stack of three pumps suggested that the individual pump discharges did not diffuse adequately after exiting from the pumps. Any high velocity in the pump discharge area is undesirable because it might attract and confuse the current-sensitive migrating fish. The CFD results also indicated that considerable recirculation was taking place above, below, and in between the pump discharge jets, thereby exacerbating the problem. Several discharge baffle arrangements were tested using FLUENT to determine a practical means of reducing the recirculation and making the discharge from each set of pumps more uniform. The most effective of these had baff les added above and below the set of pumps and diverging walls on either side of the column. The resulting discharge was characterized by a flatter velocity profile across the three pumps and only minimal recirculation above and below the set.

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Vertical and diffusing baffles on a set of pumps (top) and the resulting flow field (bottom)

The first installation of the pump array is planned to go on line in the spring of 2003 at the Rocky Reach Dam on the Columbia River in Washington. When it occurs, the project will make life better for the local fish, the local utility companies, and ITT Flygt, as similar installations are planned for the future.


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