  We numerically investigate bouncing and non-bouncing of droplets during
isothermal impact on superhydrophobic surfaces. An in-house,
experimentally-validated, finite-element method based computational model is
employed to simulate the droplet impact dynamics and transient fluid flow
within the droplet. The liquid-gas interface is tracked accurately in
Lagrangian framework with dynamic wetting boundary condition at three-phase
contact line. The interplay of kinetic, surface and gravitational energies is
investigated via systematic variation of impact velocity and equilibrium
contact angle. The numerical simulations demonstrate that the droplet bounces
off the surface if the total droplet energy at the instance of maximum
recoiling exceeds the initial surface and gravitational energy, otherwise not.
The non-bouncing droplet is characterized by the oscillations on the free
surface due to competition between the kinetic and surface energy. The droplet
dimensions and shapes obtained at different times by the simulations are
compared with the respective measurements available in the literature.
Comparisons show good agreement of numerical data with measurements and the
computational model is able to reconstruct the bouncing and non-bouncing of the
droplet as seen in the measurements. The simulated internal flow helps to
understand the impact dynamics as well as the interplay of the associated
energies during the bouncing and non-bouncing.
