Modeling instability development in layered systems

This study investigates patterns of Anger development and propagation in la yered porous media. Fingers are created with interfacial perturbations, for med by adding a thin zone of regularly varying hydraulic conductivity along the layer. Simulation results agree qualitatively with those observed in t wo-dimensional laboratory experiments. In all cases, the formation of insta bilities requires seeding of perturbations, even if the system is unstably stratified. A series of simulations show how the shapes of the instabilitie s differ according to where along the unstable interface the instabilities form and the layer in which they develop. Pathline analyses indicate how th e patterns of flow in the domain can be exceedingly complex. Concentration distributions are influenced by movements of water between layers and the f ormation of a large convection cell in the lowermost layer. These numerical investigations reinforce inferences from the experimental studies that cla ssical stability theory is less useful in determining whether instabilities will form and what their shape will be. Even with the relatively simple la yering, patterns of flow and resulting concentrations are complex. (C) 2000 Elsevier Science B.V. All rights reserved.