Finite element analysis of effect of substrate surface roughness on liquid droplet impact and flattening process

A computational program using the finite element method has been developed to simulate the impact and flattening of a metal droplet impacting onto a solid surface with different surface roughness occurring in the plasma thermal spray. The model is based on Navier-Stokes equations combining with friction conditions on the substrate surface to simulate the effect of substrate surface roughness on the flattening process of the droplet. In this study, a moving free surface model based on the Lagrangian method with an automatic adaptive remeshing technique has been developed to handle the large deformation of droplets and to ensure the computational accuracy of the numerical results. The numerical results show that the substrate surface roughness has a significant influence on the spreading velocity, flattening ratio, flattening time, splat size, and shape. The spreading process of a droplet is governed not only by the inertia and viscous forces, but also by the frictional resistance of the substrate surface.