Author(s): Maria Grazia Giordano; Andrea Montessori; Piergiorgio Fusco; Sabina Tangaro; Daniela Malcangio
Linked Author(s): Maria Grazia Giordano, Daniela Malcangio
Keywords: Buoyancy-driven flows; Computational Fluid Dynamics; Lattice Boltzmann Method; Negatively buoyant jets; Jets in crossflow
Abstract: Good 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. To this goal, a firm understanding of the complex mixing processes that effluents undergo is necessary, and numerical approaches have proven to be very useful in this respect. Modelling mixing processes and their complex nature is not an easy task, but it can provide substantial contributions in investigating jet dilution dynamics. Several numerical models have been developed to achieve this goal: those based on Computational Fluid Dynamics (CFD) have especially become more and more widespread as technology advanced, as they are free from many of the assumptions that restrict other types of models and thanks to their ability to provide a detailed description of the hydrodynamics of jet mixing processes. In the CFD field, 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 detailed 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 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 turbulent behaviour.