Three-dimensional simulation of a turbulent submerged jet interacting with a wave environment

Abstract

Industrial and domestic wastewater are usually discharged into the ocean environment as jets. The study of wave-jet interaction is fundamental to minimize the pollution of the marine environment. Dilution of wastewater into receiving waters depends on the mixing characteristics of fluids and on the turbulence characteristic of the jet. If the jet has a low Re number, the mixing will be laminar, otherwise it will be turbulent. In the laminar mixing the flow is dominated by viscous forces, and the shear generated between the ambient fluid and jet stretches the interface between them. In this mechanism, layers fold back upon themselves, overlapping. In the turbulent mixing, the flow features change in time and space. The differences in temporal and spatial velocity produce randomization of fluid particles. The turbulence features in the free, turbulent jet depend on the evolution of vortical structures. This mixing type is a highly effective mixing mechanism.As mentioned above, very often a fluid having a momentum and/or buoyancy exits an orifice and intrudes into a wider fluid unit with distinct characteristics, such as velocity, temperature, or density. Intrusions can be categorized according to whether they inject momentum, buoyancy, or both, in the ambient. Also, a jet can be classified as intermittent or continuous. Whenever a moving fluid with a velocity U0 enters a quiescent body of the same fluid, a velocity shear is generated between the entering and the ambient fluids, causing turbulence and mixing. This is, by definition, a free circular jet. The interaction between jets and waves can be analyzed both experimentally or through mathematical models and numerical simulations. These approaches allow for the analysis and understanding of the physical mechanisms behind this phenomenon, as well as the assessment of the impact of such interactions in various technical applications. In this work we refer to jets which are injections of fluid defined by momentum only. We deal with turbulent jets, which are the most frequent in real applications. A 3D Large Eddy Simulation was implemented to perform simulations of a jet, with and without waves, to examine the jet behavior in presence of waves. All simulations were run at a fixed Reynolds number value of the jet (Rej = 20000), and for different elevation values of outward waves. A preliminary simulation assuming a free surface without waves was also evaluated for reference purposes. Multiple analyses have been conducted, reporting results concerning the oscillating components, the mean velocities and the turbulent components.