A phase inversion problem with controlled thin sheet breakup *

The phase inversion physical configuration has been proposed to study the atomization of multiphase flows in a controlled set-up with low sensitivity to the boundary and initial conditions. Macroscopic quantities such as the kinetic and potential energies show convergence upon mesh refinement, while the enstrophy and the droplet size distribution do not. One reason can be found in the breakup of thin structures. A well-known drawback of the volume of fluid (VOF) method is that the breakup of thin liquid films is mainly caused by numerical aspects rather than by physical ones. The rupture occurs when the thickness reaches the order of the grid size and by refining the grid the breakup events are delayed. In this work, we present a controlled topology change algorithm to overcome the grid dependency of the breakup. First, we identify the thin films or ligaments by computing quadratic moments of the VOF indicator function. Then, we induce the breakup by making holes in the films before the thickness reaches the grid size. We show for a phase inversion problem with moderate Re and We numbers that the convergence upon grid refinement of the droplets size distribution is improved.