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Computational fluid dynamics (CFD) models, engineering theory, and practical knowledge of urban restrictions combined to produce innovative connections to combined sewer overflow tunnels. The City of Portland's Combined Sewer Overflow (CSO) program is one of the largest public works projects in the history of the State of Oregon. The program includes three large storage and conveyance projects administered by the City's Bureau of Environmental Services (BES): the Columbia Slough Consolidation Conduit (completed), the West Side CSO Tunnel (to be completed in 2006), and the East Side CSO Tunnel (2006–2011). This new infrastructure system will help reduce the frequency and volume of combined sewer overflows into the Willamette River.

The East Side CSO Tunnel is the final and largest of the projects in Portland's 20-year program to control CSOs by 2011. It will be 22 feet in diameter and over 100 feet deep. Diversion structures are required at each of the 13 existing combined sewer outfalls to connect existing overflow pipes to the East Side Tunnel. Location of these diversion structures in a highly urbanized area imposed design constraints that often resulted in configurations with complex hydraulic conditionsfor the design storm event.

This paper summarizes the use of ANSYS CFX 10.0 software to evaluate the hydraulic performance ofcomplex alternative diversion structure configurations. The software is able to represent the true flow dynamics by solving the Navier-Stokes equations using an implicit coupled solver acting upon an unstructured finite-volume mesh. The CFX postprocessor allowed the analysis team to graphically communicate diversion structure hydraulic performance issues to the design team. The interactive collaboration between the analysis team, system designers, and contractors ensured the efficient transport of flows up to 1,000 cubic feet per second (cfs) from upstream basins to the deep tunnel system.
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Document Type: Research Article

Publication date: 2006-01-01

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