Original Article Multi-component convection-diffusion in a porous medium

The stability of a triply diffusive fluid-saturated porous layer is investigated. A linear stability analysis similar to that of Pearlstein et al 1] is presented. This allows us to make a thorough investigation of the topology of the neutral curves. For some values of the thermal and solute diffusivities we obtain highly unusual neutral curves, in particular a heart-shaped, disconnected oscillatory curve. The effect of this is that three critical Rayleigh numbers are required to fully specify the linear stability criteria, a novel result in porous convection. The influence of nonlinear terms is likely to have important consequences for the experimental realisation of the linear results and so we investigate the nonlinear stability of the problem by making use of the energy method. This provides an unconditional nonlinear stability boundary and enables us to identify possible regions of subcritical instability. Received: April 4, 1996