Characterizing thin liquid sheet morphology and dynamics through topological skeletons

Thin liquid sheets are commonly seen in multiphase flows. One example is the bag breakup of a drop subjected to a uniform air stream. In the moderate Weber number regime, the originally spherical drop will deform to a bag and then break into small children drops. The liquid sheet thickness decreases rapidly over time as the bag is inflated. Measuring the thickness of the deforming, non-uniform, and curved liquid sheet obtained in interface-resolved simulation is challenging. A novel approach based on topological skeleton is proposed in this study. Skeletonization is a medial axis transformation process in which the topological features of 2D/3D objects can be captured with precision. The skeleton is the loci of centers of maximal inscribed sphere into the liquid structures, like liquid sheet. The transform takes the interfacial points and the corresponding normal from simulations and generates skeleton points and the corresponding radius of the inscribed ball. The radius for the skeleton points provides is unique and natural way to characterize local thickness of non-uniform liquid sheet of arbitrary shapes. The technique has been applied to a direct numerical simulation of aerobreakup of water drop in the bag breakup regime. The ordered skeleton points are shown to be useful to reveal morphological evolution of liquid sheets.