Experimental Studies on Vertical Dense Jets in a Flowing Current

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Experiments were performed using three-dimensional laser-induced fluorescence on turbulent vertical dense jets in flowing currents typical of brine disposal from seawater desalination plants. The flows are complex and different phenomena can dominate at different locations and at different current speeds, indicating that predicting these flows numerically will be quite challenging. At low current speeds, the rising and falling flows are almost vertical with some interference between them and the bottom flow spreads upstream as a wedge. At higher current speeds the wedge is expelled; the ascending flow is still almost vertical, but the descending flow is more gradual so the jet impacts the lower boundary farther downstream. Dilutions at the terminal rise height and impact point increase with increasing current speeds. Cross-sectional profiles of tracer concentration are neither axially or self-similar. In the descending flow, at low or intermediate current speeds, the plume is much taller than it is wide, the peak concentration occurs much closer to the top, and fluid can detrain from the jet. At higher current speeds, the profiles initially approach radial symmetry, but develop a kidney shape due to formation of two counter-rotating vortices farther downstream. These vortices cause the jet to almost completely bifurcate after impacting the bottom.