Flow structure in three-dimensional waves on a vertically falling liquid film

We have simultaneously measured the velocity vector and film thickness fields in three-dimensional (3D) waves formed upon the decay of regular 2D waves on a liquid film flowing down a vertical plate. Velocity fields at various distances from the plate surface in various regions of a 3D wave are constructed. It is shown that the liquid flow in the wave has a complex structure with regions of backflow and spanwise streams, which mainly occur under the main crest of the wave.