A New Volume-Of-Fluid Method in Openfoam

To realise the full potential of Computational Fluid Dynamics (CFD) within ma-rine science and engineering, there is a need for continuous maturing as well as verificationand validation of the numerical methods used for free surface and interfacial ows. One of thedistinguishing features here is the existence of a water surface undergoing large deformationsand topological changes during transient simulations e.g. of a breaking wave hitting an off-shore structure.

To date, the most successful method for advecting the water surface in marineapplications is the Volume-of-Fluid (VOF) method. While VOF methods have become quiteadvanced and accurate on structured meshes, there is still room for improvement when it comesto unstructured meshes of the type needed to simulate ows in and around complex geometricstructures.

We have recently developed a new geometric VOF algorithm called isoAdvector forgeneral meshes and implemented it in the OpenFOAM interfacial ow solver called interFoam.We have previously shown the advantages of isoAdvector for simple pure advection test caseson various mesh types. Here we test the effect of replacing the existing interface advectionmethod in interFoam, based on MULES limited interface compression, with the new isoAd-vector method.

Our test case is a steady 2D stream function wave propagating in a periodicdomain. Based on a series of simulations with different numerical settings, we conclude that theintroduction of isoAdvector has a significant effect on wave propagation with interFoam. Thereare several criteria of success: Preservation of water volume, of interface sharpness and shape,of crest kinematics and celerity, not to mention computational effciency.

We demonstrate howisoAdvector can improve on many of these parameters, but also that the success depends on thesolver setup. Thus, we cautiously conclude that isoAdvector is a viable alternative to MULESwhen set up correctly, especially when interface sharpness, interface smoothness and calcula-tion times are important.

There is, however, still potential for improvement in the coupling ofisoAdvector with interFoam's PISO based pressure-velocity solution algorithm.