Characterizing drop morphology evolution in aerodynamic breakup with topological skeleton

In the atomization and spray formation process, liquid structures undergo transient and complex deformation, making it challenging to characterize their morphological evolution. In the present study, a novel skeletonization method is presented to extract the topological skeleton for 2D and 3D liquid structures resolved by the Volume-of-Fluid (VOF) method. The maximally inscribed balls (MIB) within the reconstructed VOF surface are identified, and their resulting centers and radii consist of the topological skeleton. Due to numerical errors inherent in VOF-represented surfaces, erroneous skeleton points may arise. A filtering method is proposed to remove these skeleton points based on geometric properties. The skeletonization method is first tested using synthetic drop shapes composed of a superposition of spherical harmonic modes with different amplitudes. The number of skeleton branches is related to the mode number. The method is then applied to characterize the shape evolution of a drop in aerodynamic breakup. Both 2D axisymmetric and full 3D simulations are performed. The obtained curve and surface skeletons are useful for analyzing the morphological evolution of the drop and, more importantly, the sheet thickness distribution in the complex liquid bag.