Study On Horizontal Jets With Buoyancy In Shallow Waters

Submerged outfalls are widely used by coastal industrial facilities for effluent discharges. To minimize the construction cost, the outfall may be situated in relatively shallow waters, whereby the dilution is influenced by the bounded water surface and seabed together. In this case study, the mixing characteristics of horizontal jets with either positive or negative buoyancy were investigated in shallow coastal waters. The arrangement mimicked the design configuration for a large coastal facility with co-located liquefied natural gas and power generation. Both numerical simulations and experiments were carried out to examine the jet characteristics. The large eddy simulation (LES) approach with the Smagorinsky sub-grid closure was adopted in the numerical simulations. Corresponding experimental measurements were performed using the planar laser induced fluorescence technique. The results showed that the potential core of the bounded jets with buoyancy was shortened with this configuration compared to the unbounded free jets. The LES simulations were able to reproduce the geometric characteristics of the buoyant jet under the confinement of the water surface and seabed in a satisfactory manner. However, the predictions on the jet spread were relatively conservative and the minimum dilution was underestimated by about 20%-30% on average, which can be taken into account by the design calculations.