Enhancement or suppression of instability in a two-layered liquid film flow

A two-layer liquid film with a free surface falling under gravity along a stationary vertical plate is inherently unstable. It is demonstrated that the onset of instability in this inherently unstable film flow can be suppressed in certain parameter regions by imparting oscillations of appropriate amplitudes and frequencies to the plate. The regions of possible instability suppression or windows of stability are shown to depend on the particular stratifications of viscosity and density as well as the layer thickness ratio. It is shown that outside of these windows of stability, there are regions in which the instability can be enhanced. In these regions, the increased interfacial and free surface areas resulting from the enhanced instability may be exploited to promote heat and mass transfer.