We report measurements of the dynamics of an air/water interface moving through a model porous medium made of glass beads packed in a horizontal Hele-Shaw cell. At low flowrates, the interface does not move uniformly. Instead, some small regions move while others stay pinned, at least for a shea time. The burst of motion when a pinned region breaks free is called an avalanche. In several theoretical models, such avalanches were found to follow a power-law distribution. In contrast, we find that even for very slow flow: (capillary number mu U/gamma similar to 2x10(-7)) the number of avalanches of size s decays roughly exponentially with s.
Title
Distribution of avalanches in interfacial motion in a porous medium