ONSET OF THERMOSOLUTAL CONVECTIVE REGIMES IN A RECTANGULAR POROUS CAVITY

The onset of thermosolutal convection in a rectangular cell filled wit h a porous medium saturated by a binary fluid is studied. The vertical walls are maintained at different, but uniform, temperatures and conc entrations. The horizontal walls are impermeable and adiabatic. When t he ratio of resulting solutal and thermal buoyancy forces is equal to -1, we obtain an equilibrium solution corresponding to a purely diffus ive regime. We demonstrate that this regime is linearly stable up to a critical thermal Rayleigh number, Ra-c1, depending on the aspect rati o of the cell and the Lewis number. These analytical results are in go od agreement with numerical direct simulations which allow us to descr ibe the double-diffusive convective regimes taking place when the equi librium regime loses its stability.