Dynamical regimes of directional viscous fingering: Spatiotemporal chaos and wave propagation

In the opening gap between two moving surfaces, the interface between air and a viscous fluid can form a linear pattern of regular cells analogous to those of directional solidification. Depending on the values of the surface velocities, this pattern destabilizes in different ways. One regime presents the main characteristics of spatiotemporal intermittency of the type observed in the Kuramoto-Sivashinsky model. In the other, the cells become a propagative structure. Near one of the thresholds they show up as solitary waves; above, they form traveling domains of increasing size.