Two dimensional Lattice Boltzmann numerical simulation of a buoyant jet

Since its introduction (Succi, 2001), the Lattice Boltzmann Method (LBM) has obtained increasing attention in the field of Computational Fluid Dynamics, due to its intrinsic simplicity and ability even in dealing with rather complex flows. This work is aimed at assessing the ability of the two dimensional version of the LBM in simulating a buoyant jet. The latter is a saline jet, entering a uniform flow. The inlet velocity of the jet is perpendicular to the velocity of the flow. The adopted two-dimensional Lattice Boltzmann formulation is equivalent to the Navier-Stokes equation with a Boussinesque gravity force term. Experiments on turbulent negatively buoyant jets into cross flow have been utilized to assess the validity of the numerical simulations. A conductivity probe for high resolution measurement of turbulent density was utilized to measure the mixing of the salt water into the cross current, whereas the Acoustic Doppler Velocimeter (ADV) system was used for the measurement of the instantaneous threeflow velocity components. The comparison of the two dimensional numerical results with the experimental results shows that the former are able to capture the general appearance of the flow, although there are important differences. In particular, two dimensional simulations are characterised by vortices which do not appear in experiments: this is probably due to two-dimensional nature of the numerical simulation and its reduced ability in dissipating turbulent structures.