  Aerobreakup of drops is a fundamental two-phase flow problem that is
essential to many spray applications. A parametric numerical study was
performed by varying the gas stream velocity, focusing on the regime of
moderate Weber numbers, in which the drop deforms to a forward bag. When the
bag is unstable, it inflates and disintegrates into small droplets. Detailed
numerical simulations were conducted using the volume-of-fluid method on an
adaptive octree mesh to investigate the aerobreakup dynamics. Grid-refinement
studies show that converged 3D simulation results for drop deformation and bag
formation are achieved by the refinement level equivalent to 512 cells across
the initial drop diameter. To resolve the thin liquid sheet when the bag
inflates, the mesh is further refined to 2048 cells across the initial drop
diameter. The simulation results for the drop length and radius were validated
against previous experiments, and a good agreement was achieved. The
high-resolution results of drop morphological evolution were used to identify
the different phases in the aerobreakup process, characterize the distinct flow
features and dominant mechanisms in each phase. In the early time, the drop
deformation and velocity are independent of the Weber number, and a new
internal-flow deformation model, which respects this asymptotic limit, has been
developed. The pressure and velocity fields around the drop were shown to
better understand the internal flow and interfacial instability that dictate
the drop deformation. Finally, the impact of drop deformation on the drop
dynamics was discussed.
