Viscous damping and instabilities in stratified liquid film flowing down a slightly inclined plane

A reduced nonlinear model for density stratified viscous film flowing down a slightly inclined wall is derived and explored. Under buoyancy stable stratification the system exhibits various long-wavelength instabilities of noninertial, purely kinetic origin. Unlike many existing models for the film interface evolution in the present study regularization of the pertinent long-scale dynamics is provided directly by the film viscosity rather than surface tension.