Rayleigh-Taylor instability in a finely structured medium

The Rayleigh-Taylor instability in a finely layered material, with the layers oriented normally to the direction of the gravity force, is considered. It turns out that, in such a system, velocity perturbation in the most dangerous modes contains a significant and strongly nonuniform shear component that causes an increase of the viscous dissipation. Growth rates of the Rayleigh-Taylor instability for some specific examples of these fine structures are found. The conclusion is drawn that, although the viscous dissipation indeed increases, it remains insufficient to strongly reduce the growth rate of the large-scale perturbations. Possible situations where this conclusion would become invalid (and where the fine structure would produce a stronger stabilization of the global mode) are discussed. (C) 1996 American Institute of Physics.