MIXING IN A 2-LAYER STABLY STRATIFIED FLUID BY A TURBULENT JET

Mixing in a two-layer stably stratified fluid by a turbulent buoyant jet was studied primarily through a laboratory experiment. A non-swirling jet was discharged vertically downwards in a fluid system consisting initially of a top layer of fresh water and a bottom layer of salt water. In total, six experimental cases were performed where the jet exit velocity and the density difference between the top and bottom layer were varied. The total depth and the initial depth of the two layers were approximately constant in all the cases studied, and the jet exit was located in the middle of the initial freshwater layer. Both vertical density profiles and time series of density in selected points were determined from conductivity measurements using a data sampling system involving up to 16 probes. The mixing efficiency, defined as the percentage of the supplied kinetic jet energy that is used for increasing the potential energy of the fluid system, was related to a densimetric Froude number based on the intermediate layer depth. Overall, the calculated jet mixing efficiencies displayed higher values than corresponding efficiencies for destratification with air-bubble plumes.