Numerical investigation of double-diffusive (natural) convection in vertical annuluses with opposing temperature and concentration gradients

Double-diffusive convection in vertical annuluses with opposing temperature and concentration gradients is of fundamental interest and practical importance. However, available literature especially for higher Rayleigh numbers beyond Ra⩽105Ra⩽105 is sparse. In this study, we investigated double diffusion induced convection up to Ra=107Ra=107 using a simple lattice Boltzmann model. Thanks to the good stability of the present model, a modest grid resolution is sufficient for the present simulations. The influences of the ratio of buoyancy forces 0.8⩽N⩽1.30.8⩽N⩽1.3, the aspect ratio 0.5⩽A⩽20.5⩽A⩽2 and the radius ratio 1.5⩽K⩽31.5⩽K⩽3 on heat and mass transfer characteristics are discussed in detail.