Surface dilution of round submerged buoyant jets

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Abstract
The behavior of a submerged vertical round buoyant jet as it interacts with a free surface in an unstratified, stagnant receiving fluid is considered. Conventional analyses for estimating dilution within such a jet consider only the mixing due to the rising jet and neglect further dilution in the region where the jet is deflected and begins to spread radially along the surface. The present study explicitly accounts for the entrainment within a region that typically extends a few flow depths away from the source. This region is analyzed as a radial internal hydraulic jump and computational results indicate dilution increases even greater than within the submerged jet.Two experimental studies were performed to measure dilution within the radially spreading flow region and supplement data previously collected in other studies. The data indicate that the surface dilution directly above the jet can be predicted on the basis of allowing for a thin blocking layer at the surface. The data also indicate a three to fivefold increase in surface dilution across the internal jump. Both the analysis and data indicate a hydrodynamic instability for jets with low buoyancy that results in the gravitational layer locally mixing over the entire depth with some re-entrainment back into the internal jump.