Instabilities in two layer Rayleigh-Benard convection: overview and outlook

A vast amount has been learned from the single-layer Rayleigh-Benard convec tion pattern formation problem. By adding a second layer of fluid immiscibl e with the first we form a two-layer convecting system with qualitatively n ew and different phenomena possible, including competition between instabil ities in the separate layers, the driving of one pattern by another, spatio -temporal behavior at convective onset, deformations of the interface, and interfacial surface tension driven modes. The richness of the possible beha viors is impressive, owing to the large number of potentially relevant para meters. Such systems are important any time density stratification (or stra tification of thermal properties) occurs, which is the norm for situations in geophysics, atmospheric physics, astrophysics, and in industrial process es. In this paper we will describe the essential features of this Bow syste m, some of the historical background for the problem, and our current theor etical and experimental efforts on bifurcations from the conduction state i n quasi-two-dimensional channels under conditions in which buoyancy dominat es the convective behavior and the interface is flat, especially for situat ions leading to oscillatory behavior at onset. We will also describe the ex otic three dimensional flows that may exist in a system with large lateral dimensions. (C) 1998 Elsevier Science Ltd. All rights reserved.