Oscillatory Double-Diffusive Convection in a Porous Enclosure Due to Opposing Heat and Mass Fluxes on the Vertical Walls

This article adopts lattice Boltzmann method to investigate the double diffusive natural convection around a heated cylinder in an enclosure filled with porous medium. The heated cylinder is located at the center of the enclosure with high temperature and concentration. Four surrounding walls are assumed to be low temperature and concentration. The distributions of velocity, temperature and concentration are solved by three independent lattice Bhatnagar-Gross-Krook (LBGK) equations. The influence of Darcy number Da (10–4 ≤ Da ≤ 10− 2), Lewis number Le (0.2 ≤ Le ≤ 10.0) and buoyancy ratio Br (− 10.0 ≤ Br ≤ 10.0) on the double diffusive natural convection are inspected numerically. Results are presented in terms of isotherms, streamlines, isoconcentrations, average Nusselt and Sherwood numbers. At Br = − 50.0, the effect of Darcy number on unsteady flow characteristics is also investigated by the time history and phase space trajectory. It is found that the flow undergoes steady-state, unsteady doubling periodic oscillation, quasi-periodic oscillation and non-periodic oscillation when Darcy number Da is varied from 10− 4 to 10− 2.