Visualization of natural convection in ordered and disordered porous layers

The recent Modified Shadowgraphic Technique is used to study pattern formation of convecting flows in fluid saturated porous layers. Both regular and random media are explored, each exhibiting distinct primary bifurcation behavior. In regular porous layers, consisting of grids of overlapping bars, the preferred wave pattern at onset is parallel rolls with roll orientation determined by bar orientation at the upper and lower boundaries. The random medium shows a different disorganized convection pattern with each cycling through the onset of convection. The experimental work is complemented by large scale numerical simulation of large aspect ratio convection in porous layers with uniform permeability and with spatially varying permeability. The influence of the permeability field on pattern selection is explored.