Lattice Boltzmann methods for a dense vertical jet in a channel

A proper outfall design is required in order to minimize the environmental impact of the discharge of brackish water in a natural water body, which is a widespread phenomenon in areas where osmotic power plants are located. A firm understanding of the complex mixing processes that effluents undergo is needed and numerical approaches have proven to be very useful in this respect. Several numerical models have been developed to achieve this goal: among these, the Lattice Boltzmann Method (LBM) has been gaining attention during the last few years thanks to its simplicity, versatility and intrinsic parallelizability. This work focuses on the use of an LBM-based approach to perform a numerical study of a vertical negatively buoyant saline jet in a crossflow, which is a model for the release of brackish water by desalination plants in water bodies. A three-dimensional channel with a cross flow and a jet inlet on its bottom face is considered and appropriate boundary conditions are implemented, together with a gravity forcing term defined according to the Boussinesq hypothesis. The Lattice Boltzmann algorithm is used to solve both the Navier-Stokes equation and the advection-diffusion equation for the saline concentration of the jet, and a large eddy simulation (LES) model is employed in the LBM framework in order to decrease the computational cost of the numerical simulations due to the presence of turbulence. This approach is able to capture the general characteristics of the flow and shows promising results in describing the behavior of a vertical dense jet in a crossflow.