Combined action of different mechanisms of convective instability in multilayer systems

The nonlinear regimes of convection in a system of three immiscible viscous fluids are investigated by the finite-difference method. We study new phen omena caused by direct and indirect interaction of thermocapillary and buoy ancy (Rayleigh and anticonvective) instability mechanisms. Two variants of heating-from below and from above-are considered. The interfaces are assume d to be flat. We focus on nonlinear evolution of steady and oscillatory mot ions and selection of stable convective structures depending on the paramet ers of systems. The influence of the lateral boundary conditions is also in vestigated. A classification of different variants of interaction between R ayleigh and thermocapillary instability mechanisms is presented, and severa l typical examples are studied. Specifically, we considered six different c onfigurations here the Rayleigh convection arises mainly in a definite laye r, and the thermocapillary convection appears mainly near the definite inte rface. Also, the case where both interfaces are active and alternatively pl ay a dominant role is investigated. Some configurations of interaction betw een anticonvective and thermocapillary instability mechanisms are considere d.