Fingering in Two-Dimensional, Homogeneous, Unsaturated Porous Media

The onset of fingering during the redistribution of liquid is verified for homogeneous media using water and silicon oil. The initial instability is due to air entrainment through the top surface of the medium by which an opposing force field is created for the downward infiltration. Development of fingers is brought about by the pressure difference created laterally due to the air-water interfaces, which makes the liquid converge toward fingers. A model medium, constructed with a series of vertical tubes whose diameter varies sinusoidally, can reproduce the fundamental features mentioned above.