a b s t r a c tIn this work, a linear stability analysis is used to investigate a capillary surface waves between two horizontal finite fluid layers. The system is acted upon by a vertical periodic electric field. The problem examines few representatives of porous media. It is also includes finite conductivity, mass and heat transfer. It is assumed that the basic flow is two-dimensional streaming flow. A general dispersion relation governing the linear stability is derived. In contrast with our previous work [23], the present problem shows that the stability criterion depends on the mass and heat transfer parameter. The present study recovers some special cases upon appropriate data choices. The presence of finite conductivity's together with the dielectric permeability's make the uniform electric field plays a dual role in the stability criterion. This shows some analogy with the nonlinear stability theory. In addition, the mass and heat transfer parameter as well as the Darcy's coefficients play a stabilizing role in the stability picture. In case of the Rayleigh-Taylor instability, by means of the Whittaker technique, the parametric excitation of the electrohydrodynamic surface waves is obtained. The transition curve equations are calculated up to the fourth order for a small dimensionless parameter. The analytical results are numerically confirmed.Ó 2010 Elsevier Inc. All rights reserved.
The introductionThe instability of a plane interface between two superposed fluids of different densities, when it occurs, is called the Rayleigh-Taylor instability (RTI). This instability was first investigated by Rayleigh [1]. Taylor [2] studied the stability of a heterogeneous fluid accelerated in a direction perpendicular to the plane of stratification. The RTI has been addressed in several studies owing to its importance in stratified system, among which planetary and stellar atmosphere are of two examples. The effect of the external forces has an importance, mainly, in planetary and stellar systems. Coriolis and centrifugal forces are more common in these systems. They play an important role in determining many phenomena including the RTI. Different properties of fluids have been included in the RTI through theoretical investigation. Chandrasekhar [3] has given a detailed account of these investigations. The Kelvin-Helmholtz instability (KHI) arises when two superposed fluids are in relative motion. The model of the classical KHI involves a horizontal interface between two fluids with different parallel, uniform, and horizontal velocities. In the KHI problem, the effect of streaming is destabilizing in the sense as given by Chandrasekhar [3]. This instability, which arises as a consequence of a relative drift velocity of two fluids along the surface of discontinuity, has a great relevance to various physical phenomena such as commentary tails and the magnetospherical boundary. The KHI has attracted the attention of many researchers, due to shear flow in stratified fluids, and its dominant 0307-904X/$ -see front matter Ó