DEFECTS IN WETTING FRONTS - EXPERIMENTAL AND THEORETICAL RESULTS

We study flow in a porous medium in the presence of a discontinuous pe rturbation (defect) that perturbs its parameters. The discontinuous pe rturbation is at the interface between regions of different porosities , produced in the experiment by uniformly depositing black toner with a laser printer. When water propagates in such a medium the wetting fr ont develops a nontrivial, curved steady state solution. We present ex perimental measurements of the profiles and their propagation rate, as well as the characteristics of the steady state solution. A naive att empt to use perturbation theory fails due to discontinuities at the '' defect.'' We proceed to develop a theoretical treatment based on Lapla cian flow, that is good to ail orders and predicts most of the feature s that can be observed. We find good quantitative agreement between th eory and experiment, without any fit parameters.