Lattice Boltzmann simulations of the double-diffusive natural convection and oscillation characteristics in an enclosure with Soret and Dufour effects

Lattice Boltzmann method (LBM) is used for examining the double-diffusive natural convection around a heated cylinder in a square enclosure with Soret and Dufour effects. The inner heated cylinder is positioned at the square enclosure center with high temperature and concentration. Four surrounding walls are rigid non-slip surfaces with low temperature and concentration. The distributions of velocity, temperature, and concentration are solved by three independent lattice Bhatnagar-Gross-Krook (LBGK) equations combined into a coupled equation through the Boussinesq approximation. The Soret and Dufour effects are involved in the equilibrium distribution functions of C-i(eq) and T-i(eq), respectively. The influences of Soret number S-r (0.0 <= S-r <= 0.8) and Dufour number D-f (0.0 <= D-f <= 0.8) combined with buoyancy ratio Br (-10 <= Br <= 10) on double-diffusive natural convection are investigated numerically. Results are presented in terms of streamlines, isotherms, iso-concentrations, average Nusselt and Sherwood numbers. Furthermore, time history and phase space trajectory are used to investigate the effects of Soret and Dufour numbers on unsteady flow characteristics at a high Rayleigh number (Ra = 5 x 10(6)). Results indicate that heat and mass transfers are weakened with simultaneous increasing D-f and S-r and the flow stability can be enhanced.