Rebound of a droplet impacting a non-wetting rigid surface*

We study a fluid droplet's impact onto and rebound from a horizontal non-wetting surface in the inertio-capillary regime. Controlled experiments are carried out using a custom piezoelectric droplet generator and imaged using a high-speed camera. A reduced-order fluid model is developed and used to study droplet deformations and trajectory, and is based on a spectral method that decouples the fundamental modes of droplet oscillation into a set of non-interacting damped harmonic oscillators. The contact mechanics of the droplet impact are solved using a method that imposes only natural geometric and kinematic constraints and provides the evolution of the contact area and pressure distribution as part of the solution of the resulting system of equations. We study a number of impact metrics, such as coefficient of restitution, contact time, and minimum height of the center of mass and their dependence on the dimensionless parameters that govern the problem. Predictions of our model are compared to  experimental measurements and predictions obtained from direct numerical simulations. Insights gained from this model can contribute to the development of reduced-order models that are computationally inexpensive.