Two-dimensional simulation of liquid metal spray deposition onto a complex surface: II. splashing and redeposition

摘要

A two-dimensional model (Djuric Z, Newbery P and Grant P 1999 Modelling Simul. Mater. Sci. Eng. 7 553) of liquid metal spray deposition on an arbitrary surface has been extended to include the important processes of splashing of spray droplets during collision with the surface, and the subsequent redeposition of scattered material. Every point on the surface has been treated as both a receiver and an emitter of sprayed material. The action of these micro sources has been modelled by several assumed micro source functions of the spatial distribution of splashed material. The moving surface has been traced by following the trajectories of its points as spraying proceeds. These trajectories were calculated in a way similar to that used previously (Djuric Z, Newbery P and Grant P 1999 Modelling Simul. Mater. Sci. Eng. 7 553), except that they now can, in principle, intersect each other. To achieve a physically reasonable solution, a new algorithm has been developed to resolve this problem. The model has been applied in several cases and the simulations compared with experimental results. By including or excluding droplet splashing effects, it has been possible to analyse the importance of redeposition both in simulations and experiments. In the case of splashing, different assumed micro source functions resulted in slightly different but geometrically similar predicted shapes. The modelling of these functions was based on the concept of the continuity of splashing and re-emission processes, a simplicity of the point source, a qualitative analysis of splashing events observed in experiments by high-speed imaging, the total mass preservation constraint, and some theoretical and experimental results of a single droplet impact onto a hard surface. Using these results, it was possible to predict where direct spraying dominated deposit growth, and where the subsequent redeposition had a major influence on deposit growth and the final shape. While in some cases model predictions are in reasonable agreement with available experimental data, the limitation of the model in accurately describing three-dimensional effects during droplet splashing has been revealed.