Level-set method for the modelling of liquid bridge formation and break-up

In this paper, a level-set method is used to track the free surface and velocity profile of a Newtonian filament being stretched on an extensional rheometer. The method enables simulations to be performed from initial stretching until after the filament has broken up. The method used also follows the behaviour at the plate-liquid interface, allowing the air–liquid–solid contact point to move freely rather than being pinned at the edge of the plate. The simulations were validated by comparison with analogous experiments with glycerin, with excellent agreement between the two. The simulations were able to track the free surface throughout the experiment, including after the topological change associated with the filament breaking up. For the modelling of the fluid stretching, a novel grid deformation algorithm was introduced which allowed a tailored expansion of the domain, avoiding the need for specialised re-meshing.