Differential diffusive instabilities of miscible two-layer stratifications in porous media and Hele-Shaw cells

Differential diffusive instabilities of miscible two-layer stratifications in porous media and Hele-Shaw cells

Gopalakrishnan, S.S.
Carballido-Landeira, J.
De Wit, A.
Knaepen, B.

2015-08-26

In porous media, a stratification of a given solution on top of another miscible solution can be buoyantly unstable because of an unstable density stratification or because of differential diffusive effects. The former is the well known Rayleigh–Taylor (RT) mechanism wherein the interface is destabilized by the denser solution overlying a less dense one in the gravity field. Whereas the latter is of particular interest in the field of oceanography, when the upper solution is less dense than the lower one with the lower component diffusing faster than the upper one, resulting in a double diffusive (DD) instability. Similarly, a diffusive-layer convection (DLC) instability has also been observed for a stable density stratification with the upper solute diffusing faster than the lower one. Though the literature on differential diffusion effects is pretty vast, very few studies have managed to establish a connection, both qualitatively and quantitatively, between numerical simulations and experimental observations, which is the basis of the present study. We report our findings in a broad parameter range where the instability mechanism could be triggered by an unstable density stratification or due to differential diffusive effects, or even both, resulting in mixed modes.

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(c) 2015 the Authors