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Three-Dimensional CFD Modelling of Mixing and Dispersion from Marine Outfall Discharges

Author(s): Claudia Castro-Faccetti

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Keywords: CFD; RANS; Marine outfall; Buoyant jets; Near field;

Abstract: Municipal and industrial wastewater is commonly discharged into coastal waters via ocean outfalls. Accurate prediction of mixing and dispersion of such wastewater is important to prevent significant negative effects on the water quality of the receiving environment. Traditional modelling approaches predict dilution in the near field based on length-scale or entrainment models, whereas the far field is simulated using coastal circulation models. CFD approaches have been scarcely used to model both regions, despite their great potential. This study presents the validation of near field simulations from single and multiple ports discharges at laboratory scale using three-dimensional, time-dependent RANS k-ℇ and k-ω SST turbulence models. Water density is defined as a function of temperature and salinity using the UNESCO seawater state equation. To overcome the difficulties arising from the different length scales of the discharge ports and the receiving water body, a mesh adaptation approach is implemented. Predictions of flow trajectory, velocity and dilution show generally good agreement with available experimental values, providing higher accuracy than widely used modelling packages such as CORJET, VISJET and UM3 for dilution predictions. The validated methodology is then applied to the three-dimensional, time-dependent simulation of a full-scale real-life ocean outfall in Cartagena, Colombia, under varying conditions. This study has found that a RANS modelling approach can be a valuable technique for the simulation of buoyant jets from real-life marine outfalls.

DOI: https://doi.org/10.3850/38WC092019-0757

Year: 2019

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