THERMOHALINE CONVECTION IN A POROUS-MEDIUM HEATED FROM BELOW

Results from numerical experiments of convection in porous media heated from below with two opposing sources of buoyancy (e.g. heat and salt) are presented. Steady-state calculations with a 'salted from below' boundary condition on composition and Dirichlet conditions on temperature in the region 100 < Ra < 600, 10 < Le < 100, 0 < R-rho < 0.4 show that Nu is-proportional-to Ra3/5 (1 - R-rho)1/2 and Sh is-proportional-to Ra3/5 Le1/2 x (1 - R-rho)1/2. Time-dependent simulations with phi(*) = 1 show that flows depend dramatically on R-rho at constant Ra and Le. When the system is 'salted from below', the dynamics change with increasing R-rho from a system which evolves to a well-mixed convective steady-state, to one in which flow is chaotic with large amplitude fluctuations in composition, and finally to one which evolves to a conductive steady-state. For an initially layered salinity field, vertically stacked convection cells may exist transiently; the interface between the layer is highly unsteady.