Numerical Simulation Of Droplets Impact Onto Solid Surfaces By The Lattice-Boltzmann Method

Droplets of liquid impact onto solid surfaces exist widely in the nature as well as in engineering and technical fields. The dynamic behaviour of droplet impact onto solid surface plays an important role in the study of nature phenomenon and the development of industrial technology. There is a difficulty to track exactly the deformation interface when the conventional simulation methods are used in this phenomenon.The lattice-Boltzmann method (LBM) has recently emerged as a powerful tool of computational fluid dynamics, it has the advantage of depicting the interaction between different phases because of its microcosmic characteristic. The interparticle potential model proposed by Shan and Chen can automatically track the location of free interface, and it is easy to deal with the boundary conditions, hence the calculation efficiency is very high.In order to prove the ability of the LBM in the fluid simulation, a single phase model was constructed and was used to simulate the cavity and poiseuille flows. On the base of the single phase model, a two-phase potential model was built and validated through the simulation of the two droplets coalescence. Then droplets impact onto horizontal and inclined surfaces were investigated by this two-phase model. The flow state of the droplet on the surface is analyzed in detail, and the effects of surface characteristic, impact velocity, impact angle, the viscosity and surface tension of the liquid are investigated, respectively.The results has shown in the case of normal impact, the flow is symmetric, but it is asymmetric for the oblique impact. The flow state is seriously influenced by the wettability of the surface. In the simulation of normal impact, the phenomenon of deposition and rebounding can be obtained. During the process of droplets impact onto inclined surfaces, the droplet may spread, spread and slide on the surface and rebound from the surface. The effect of the impact velocity for the normal and oblique impact is same at the spread stage, that is the maximum relative diameter and spreading speed increase with increasing the impact velocity, and the recoiling speed for the normal impact also increases. The influence of the impact angle on the oblique collision is that the maximum relative diameter and spreading speed decreases with impact angle except in the early stage. The liquid characteristic such as viscosity and surface tension has significant influence to the droplet impact dynamics. The smaller of the liquid viscosity, the bigger of the maximum relative diameter of the droplets can be obtained. The surface tension has no effect on the spreading process, but for the recoiling process, the surface tension is bigger, the recoiling speed is faster, and the droplet is more possible to rebound from the surface.