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Effects of horizontal gradients on thermohaline instabilities in infinite porous media. (English) Zbl 0779.76026

Thermohaline instabilities produced by horizontal gradients of temperature and salinity in a saturated homogeneous isotropic infinite porous medium are studied by using linear stability analysis. Though in several situations of geological interest the horizontal gradients are as strong as the vertical ones, the effect of the former ones has not been studied neither theoretically nor experimentally in porous media. Previous results refer to Newtonian fluids without any porous matrix [J. Y. Holier, J. Fluid Mech. 137, 343 ff. (1983)]. In the reference state, the horizontal gradients of temperature and salinity are mutually compensating so that the density does not vary horizontally. It is found that the mentioned reference state is always unstable: the effective advection rates of heat and dissolved salts are different so that any disturbance involving a horizontal displacement creates a net horizontal density gradient and destabilizes the system. The authors study the typical velocity fields after perturbation. For positive vertical Rayleigh numbers, the velocity field is mainly vertical (salt fingers) whereas when it is negative the velocity field is almost horizontal (interleaving). The perturbed fluxes tend always to reduce the initial concentration gradients and typically also the gravitational potential energy of the fluid: this may lead to downwards accumulation of soil contaminants.
Reviewer: D.Jou (Ballaterra)

MSC:

76E20 Stability and instability of geophysical and astrophysical flows
76S05 Flows in porous media; filtration; seepage
80A20 Heat and mass transfer, heat flow (MSC2010)
86A05 Hydrology, hydrography, oceanography
86A60 Geological problems
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