Numerical investigation of volume of fluid and level set interface capturing methods for bubble growth and detachment

Abstract

The injection of an air bubble in a liquid at rest is an interface flow problem where surface tension and its modeling at solid boundaries is a key factor. It is the subject of this study. Numerical simulations have been performed to study 3D axi-symmetrical bubble growth from an orifice through a horizontal wall. The gas inflow velocity used was sufficiently small to ensure that the bubble growth is quasi-static so that surface tension and buoyancy forces are dominant. The wall was considered non-wettable to avoid spreading of the interface along the wall. The Navier-Stokes equations were solved with two different interface capturing methods based on Volume of Fluid (VOF) and Level Set (LS) as well as coupled CVOFLS. In the VOF method the bubble interface was tracked using either an algebraic solver which results in some diffusion of the interface (compressive scheme implemented in OpenFOAM), or it was determined using a geometric reconstruction scheme (Geo-Reconstruct Scheme from Fluent). The TransAT code was used for the LS model which captures the interface using signed distance function. The bubble volume and center of gravity have been investigated during the growth using the three solvers and numerical results have been assessed against experimental data. These results have shown that reconstructing the interface using the LS method gives good agreement with the experiments. In VOF (compressive scheme), the bubble detaches at earlier times resulting in a smaller detachment volume. The coupled CVOFLS-GeoReconstruct was found to be more computationally expensive than the VOF-GeoReconstruct and to present bubble oscillation during the growth. © Published under licence by IOP Publishing Ltd.