  We analyze the flow of a planar gas jet impinging on a thin film, dragged by
a vertical moving wall. In the coating industry, this configuration is known as
jet wiping, a process in which impinging jets control the thickness of liquid
coatings on flat plates withdrawn vertically from a coating bath. We present
three-dimensional (3D) two-phase flow simulations combining Large Eddy
Simulation (LES) and Volume of Fluid (VOF). Three wiping configurations are
simulated and the results are validated with experimental data from previous
works. Multiscale modal analysis is used to analyze the dynamic interaction
between the gas flow and the liquid film. In particular, we present a
combination of Multiscale Proper Orthogonal decomposition (mPOD) and
correlation analysis. The mPOD is used to identify the dominant travelling wave
pattern in the liquid film flow, and the temporal structures are used to
determine the most correlated flow features in the gas jet. This allows for
revealing a two-dimensional (2D) mechanism for wave formation in the liquid
coat. Finally, we use the numerical results to analyze the validity of some of
the critical assumptions underpinning the derivation of integral film models of
jet wiping.
