Thermohalin≐ convection in a porous medium heated from below

Abstract

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 < Rp < 0.4 show that Nu ∞ Ra 3 5 (1-Rρ) 1 2 and Sh ∞ Ra sol3 5 Le 1 2 × (1-Rρ) 1 2 . Time-dependent simulations with φ ∗ = 1 show that flows depend dramatically on Rρ at constant Ra and Le. When the system is ‘salted from below’, the dynamics change with increasing Rp 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.