High Rayleigh number convection in a fluid overlaying a porous bed

A series of numerical experiments concerning the phenomenon of natural convection in a two-layer composite system heated from below is reported. The composite system consists of a fluid layer bounded from below by a porous bed saturated by the same fluid. The numerical solutions are based on the full equations for time-dependent flow, and document the main features of the flow at Rayleigh numbers several orders of magnitude above critical value. The ranges covered by the numerical solutions are 102–106 for overall Rayleigh number, 10−7–10−4 for Darcy number, and 0.2–1 for the height to length ratio of the composite system