Stabilizing the unstructured Volume-of-Fluid method for capillary flows in microstructures using artificial viscosity

Parasitic currents still pose a significant challenge for the investigationof two-phase flow in Lab-on-Chip (LoC) applications with Volume-of-Fluid (VoF)simulations. To counter the impact of such spurious velocity fields in thevicinity of the fluid interface, this work presents an implementation of anartificial interface viscosity model in OpenFOAM. The model is introduced as anadditional dampening term in the momentum conservation equation. It isimplemented as a fvOption, allowing for its simple application to existing VoFsolvers. Validation is performed with hydrodynamic and wetting cases, in whichconstant artificial viscosity values are prescribed to examine the sensitivityof the solution to the artificial dampening. The artificial viscosity modelshows promising results in reducing spurious currents for two consideredgeometrical VoF solvers, namely interIsoFoam and InterFlow. It is found thatthe influence of the artificial viscosity heavily depends on the fluidproperties. Applying the model to simulations of an interface traversingthrough microcavities relevant in LoC applications, experimental results of theinterface progression are predicted well, while spurious currents areeffectively reduced by approximately one order of magnitude due to theartificial viscosity model. The code is publicly available on GitHub(https://github.com/boschresearch/sepMultiphaseFoam/tree/publications/ArtificialInterfaceViscosity).