On dimpled thin liquid falling films

The interfacial dynamics of a thin liquid falling film flowing on a plane inclined with respect to gravity is investigated. The glycerol-water mixture is recirculated through the experiment, and after a significant time, isotropic, transient depressions along the fluid surface appear and disappear. The locations of these events, which we call ``dimples'' are shown to be independent of spatial location, and are more pronounced as the average film thickness is reduced. Potential mechanisms for this transient behavior could involve large Peclet-number dynamics of soluble surfactant, Marangoni and inertial fluid effects and shear-induced migration of particles within the bulk. Comparison of the theory to the experiment is presented.