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The U.S. Army Corps of Engineers (USACE), Portland District is considering blocking the upper 12.3 m 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. RÉSUMÉLe U.S. Army Corps of Engineers (USACE), du district de Portland envisage bloquer les 12.3m supérieurs des prises d'eau au barrage de Dalles, Orégon avec un trashrack bloqué en forme de J (un panneau en acier devant le trashrack existant). L'objectif est de créer une configuration d'écoulement facilitant la migration descendante des jeunes poissons. Un modèle numérique d'écoulement tridimensionnel (CFD) d'une unité de turbine du barrage a été développé pour étudier l'impact du trashrack bloqué proposé sur l'hydraulique de prise de la turbine. Le modèle a été vérifié en comparant des distributions de vitesse dans un modèle physique au 1/25 du centre de recherches et de développement d'enginerie (ERDC), Vicksburg, Mississippi. Les simulations numériques indiquent que le trashrack bloqué crée une tranquillisation, près de la zone morte d'écoulement au-dessus. Au-dessous du trashrack, l'écoulement est relativement plus horizontal dans les prises de turbine. Cependant, les distributions de vitesse à l'intérieur des prises sont sensiblement moins uniformes. Des zones mortes d'écoulement sont créées dans les régions immédiatement derrière le trashrack bloqué. Les distributions transversales de vitesse montrent de forts tourbillons dans la prise. L'analyse montre la nécessité d'étudier la conception améliorée de prise de turbine quand il faut adapter aux barrages existants des équipements pour de jeunes poissons.

Computational fluid dynamics (CFD) modelling in the wastewater treatment (WWT) field is continuing to grow and be used to solve increasingly complex problems. However, the future of CFD models and their value to the wastewater field are a function of their proper application and knowledge of their limits. As has been established for other types of wastewater modelling (i.e. biokinetic models), it is timely to define a good modelling practice (GMP) for wastewater CFD applications. An International Water Association (IWA) working group has been formed to investigate a variety of issues and challenges related to CFD modelling in water and WWT. This paper summarizes the recommendations for GMP of the IWA working group on CFD. The paper provides an overview of GMP and, though it is written for the wastewater application, is based on general CFD procedures. A forthcoming companion paper to provide specific details on modelling of individual wastewater components forms the next step of the working group.

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