Impact of Spinning Droplets onto Superhydrophobic Surfaces: Asymmetric Tumbling Rapid Rebound

Abstract

The impact dynamics of spinning droplets onto superhydrophobic surfaces was studied by using Volume-of-Fluid simulations, covering broad ranges of Weber number ($We$) and dimensionless angular velocity ($\mathit{\Omega}$). The omputational results were validated by high-speed imaging experiments, with particular focus on the types of rebound, asymmetric deformation, and droplet-wall contact time. Results show that, the spinning motion of droplets leads to two novel rebound scenarios. Specificially, the front-raise tumbling rebound occurs at a lower $\mathit{\Omega}$ and is caused by the unsymmetrical Laplace pressure, while the rear-raise tumbling rebound emerges at a higher $\mathit{\Omega}$ and is attributed to the rotational inertia. The angular momentum of the spinning droplet is dissipated or even reversed, while its direction upon detachment is inconsistent with the visually observed spinning motion. With the increase of the angular velocity, the droplet-wall contact time is largely reduced, which is attributed to the asymmetric spreading by the spinning motion rather than the increased kinetic energy. A theoretical model was also established to predict asymmetric spreading and the contact time and validated against numerical results in wide ranges of $We$ and $\mathit{\Omega}$.