Adaptive time-step selection in volume of fluid (VOF) simulations

In numerical simulations, Volume of Fluid (VOF) approach is a well-established method in capturing the interface and solving multiphase problems. However, choosing the appropriate time step can be a challenging task for majority of users both with commercial software as well as in house codes. Therefore, we implemented a CFL based time-step control that can target a given area such as the cells intersecting the free surface, such that the CFL limit can be imposed where it is needed. In addition, we keep the sub-steps constant. This enhancement is useful in casting, tank sloshing and marine applications.
In this presentation, we focus on a tank sloshing simulation with Simcenter STAR-CCM+ aiming to demonstrate the merits of using adaptive time-step for VOF multi step simulations. We highlight the add on value from two perspectives 1) reduction in overall computational time for a range of transient examples that are known to have non-constant timescales, 2) demonstrate an improvement in convergence compared to a constant time step set at the average of the variable timestep run.