Verification of Volume-of-Fluid (VOF) simulation for thin liquid film applications

This paper describes the application of the built-in Volume-of-Fluid (VOF) model in the commercial Computational Fluid Dynamics (CFD) software FLUENTTM and the verification of its accuracy. As the VOF model is based on the field volume fraction calculations and surface reconstruction methods, in which a free surface is not explicitly tracked, the aim was to verify that a reconstructed surface obtained by VOF simulation is representative of a real surface. For this purpose, various cases of a thin liquid film flowing into rectangular cavities were simulated and the resulting surface profiles analyzed in terms of the normal velocity of the constructed surface, which should be zero in a real surface. Both the cases of small and large surface tension coefficients were simulated and the results showed that the VOF model is capable of generating surface profiles with reasonably accurate normal velocity condition for the cases with small or no surface tension. For high surface tension values, the existence of spurious interface velocity as previously reported in the literature was confirmed. Comparisons of the VOF-calculated surface profiles with the ones obtained using the explicit surface tracking algorithms such as the Boundary Element Method (BEM) reported in the literature showed that the VOF model is able to produce the expected profiles of thin liquid film flowing a two-dimensional rectangular cavity and thus can be considered for simulation of other applications involving thin liquid film flows, provided the grid refinement based on the volume fraction gradient is applied.