  We perform numerical simulations to study the dynamics of the entry of
hydrophobic spheres in a pool of water using ANSYS. To track the air-water
interface during the translation of the sphere in the pool of water, we use the
volume of fluid (VOF) model. The continuum surface force (CSF) method computes
the surface tension force. To simulate the hydrophobic surface properties, we
also include wall adhesion. We perform simulations with different diameters and
impact speeds of the sphere. Our simulations capture the formation of different
types of air cavities, pinch-offs of these cavities, and other finer details
similar to the experiments performed at the same parameters. Finally, we
compare the coefficient of drag among the different hydrophobic cases. We
further perform simulations of hydrophilic spheres impacting the pool of water
and compare the drag coefficient with the analogous hydrophobic cases. We
conclude that the spheres with hydrophobic surfaces have a lower drag
coefficient than their hydrophilic counterparts. This lower drag of the
hydrophobic spheres is attributed to the formation of the air cavity by the
hydrophobic surfaces while translating through the pool of water, which reduces
the area of the sphere in contact with water. In contrast, no such air cavity
forms in the case of hydrophilic spheres.
