A numerical study of the droplet impact dynamics on a two-dimension random rough surface

Considerable efforts had been devoted to investigating numerically the droplet impact dynamics on a superhydrophobic surface. Whereas most of these numerical simulations were restricted to the two-dimension (2-D) axisymmetric coordinate system with the one-dimension (1-D) substrate surface. In this work, a three-dimension (3-D) computational fluid dynamics (CFD) model, which intergrew a 2-D random rough surface, was proposed to investigate the droplet impact dynamics, and the multi-phase flow issue was solved by the Navier-Stokes equations. It is remarkable that the 3-D CFD model revealed several significant dynamic details that were not easily captured in a 2-D axisymmetric coordinate system or practical experiments. For instance, the 3-D CFD model provided a unique perspective to understand the varying dynamic behaviors of impinged droplet in terms of the velocity streamline and dynamic viscosity analyses. Herein, the dynamic viscosity diagram revealed that the sprawl droplet on the 2-D random rough surface was classified as Cassie state, while as Wenzel state for smooth surface, which also explained the better bouncing behaviors of droplet from the random rough surface. Accordingly, we suggested a visual way to evaluate the solid-liquid contact area surrounded by the triple-phase contact line. The effects of finger protrusion and central cavity growth from the sprawl droplet on the vortex generation were further analyzed on the ground of the velocity amplitude distribution and streamline data. The present work can provide early guidance to inquire into the impact dynamics of droplets on the random rough surface.