Experimental and Numerical Study on the Effects of Waves on Mixing of Negatively Buoyant Jets

With the extensive development of desalination, power and petrochemical plants and refineries in recent years, it is necessary to evaluate their environmental impacts. Desalination plants remove the dissolved minerals from coastal water bodies and produce effluents with a different density than the ambient water, which can lead to major problems in the ecosystem. When the jet is discharged into coastal waters, due to the existence of waves, more complex mixing processes may occur, and thus significantly affect the jet dilution processes compared to the case when the jet is discharged into a stagnant ambient.

This paper presents the results of an experimental and numerical study on inclined negatively buoyant jets released in a receiving water body with waves, such as in the case of brine discharges from desalination plants into coastal water bodies. The experimental measurements were performed using a combination of Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF) techniques, to measure the time-histories of the velocity and concentration fields. The wave and current characteristics were chosen to simulate a typical effluent discharge into the Mediterranean Sea.

A three-dimensional numerical model of inclined negatively buoyant jets discharging into wavy ambient is also investigated in this paper. The numerical model (OpenFOAM) used in this study is based on the Finite Volume Method (FVM) and the performance of Reynolds-Averaged Navier-Stokes (RANS) model is investigated. The Volume of Fluid (VOF) Method was employed to model free surface dynamics.

The influence of the wave motion on the inclined negatively buoyant jet geometry resulted in the jet rotation and increase in the jet width. This can result in a decrease of the maximum height and a higher dilution under wave conditions. Simulation results are also presented and compared with measured values to investigate the performance of the numerical simulation. The empirical formulas proposed as a result of accurate measurement in this study will provide novel insights into the design of outfalls in coastal waters.