ABSOLUTE INSTABILITIES IN 2-LAYER GRAVITY-DRIVEN FILM FLOW WITH A FREE-SURFACE

We investigate on the basis of a linear analysis the stability of a gr avity driven laminar, stratified film flow of two superposed fluids wh ich are a clear liquid and a suspension of solid particles below. The study is based on the assumption that the concentration remains consta nt within the suspension layer. This assumption is justified because o f the base-state results for shear induced resuspension for even moder ate Row-rates. The numerical solutions display the existence of two di fferent instabilities: waves at the free surface and interfacial waves . Here we concentrate on the latter instabilities and show that such a gravity driven two-layer film flow with a free surface is absolutely unstable.