Dense Jet Discharges in Shallow Water

摘要

Extensive Experiments on inclined dense jets typical of brine discharges into shallow water are reported. The experiments were conducted with nozzles oriented at 30 degrees, 45 degrees, and 60 degrees to the horizontal and the spatial variations of tracer concentrations were measured by three-dimensional laser-induced fluorescence (3DLIF). Three flow regimes were identified: deep water, surface contact, and shallow water. The regimes depend on the value of dF/H, where d is the nozzle diameter, F the jet densimetric Froude number, and H the water depth; criteria were presented for the transitions between them. Flow images revealed complex three-dimensional interactions with the free surface, especially for steep nozzle angles in shallow water. Dilutions at critical points and their locations were measured. For deep water, all results followed those previously reported for fully submerged jets. As the depth decreases (or dF/H increases) to the surface contact regime, dilutions begin to decrease. Tracer concentration profiles are truncated at the water surface and in shallow water resemble half-Gaussian profiles similar to those of wall jets. The jets can cling to the water surface, although the locations of the bottom impact point and near-field length are not significantly affected by the water surface. In deep water and surface contact regimes, the impact point and near-field dilutions are highest for 60 degrees nozzles. As the depth decreases further, however, the dilutions for the three nozzle angles become approximately equal, until, for shallow water, the 30 degrees-nozzle gives slightly higher dilution. The 30 degrees-nozzle may be preferable for this case because there is less surface interaction and, therefore, less visual impact on the water surface. Previous recommendations that dense jets be submerged so that the rise height to the jet's upper boundary be less than 75% of the water depth to avoid surface effects appear to be overly conservative and the present results suggest that the rise can be as much as 90% of the water depth for all angles with no deleterious effect on dilution. (C) 2015 American Society of Civil Engineers.