Simulation Of Droplet Sliding On Chemically Heterogeneous Surfaces Based On Lattice Boltzmann Method

The sliding behaviour of droplets on surfaces is widely found in nature and in engineering.With the development of bionics,people have gradually applied it to industrial fields such as self-cleaning,fresh water harvesting,printing,spray cooling and microfluidics by observing the sliding characteristics of droplets on various biological and animal surfaces in nature,which has a great impact on our lives.The study of droplet sliding behaviour on solid surfaces is an important fundamental theory for the development of traditional industries and the promotion of innovative frontier technologies.In particular,understanding the effect of solid surface heterogeneous properties on droplet sliding in real surfaces is key to accurately controlling and predicting droplet motion on solid surfaces.There has been a wealth of research results on droplet sliding at domestic and international level,but due to the complex interaction between droplets and solid surfaces,the droplet sliding behaviour is complex and variable,especially due to the dynamic gas-liquid interface changes and microscale interface effects involved in the process.The Lattice Boltzmann Method(LBM)is a mesoscopic scale numerical simulation method between the macroscopic and microscopic scales,suitable for the study of the dynamic behaviour of tiny liquid droplets.It is relatively intuitive when dealing with fluidsolid interactions due to its property of describing particle motion,and is able to describe the fluid-solid interactions intuitively and accurately.Therefore,in this paper,a kinematic model of a three-dimensional droplet sliding on a heterogeneous surface is developed based on the lattice Boltzmann method,and various quantitative analyses are carried out to reveal the sliding pattern of the droplet on an inclined substrate.The main work is as follows:(1)Based on the Boltzmann model of the chemical potential lattice,a droplet sliding model is developed on a chemically heterogeneous surface with a chemically heterogeneous step formed by a jump in the properties of the solid surface from hydrophilic to hydrophobic based on a chemically heterogeneous tilted surface is considered.The chemical potential is used to calculate non-ideal forces to control the automatic evolution of the gas-liquid interface,and the chemical potential wetting boundary conditions are used to accurately and flexibly describe the flow-solid interaction,reproducing the three equilibrium states reported in previous studies,providing an effective simulation environment for accurately modelling droplet sliding on heterogeneous surfaces.(2)The influence of the strength of chemically heterogeneous steps on the sliding behaviour on inclined surfaces is studied and analysed.Through simulation,we have analysed the deformation pattern of the droplet,the velocity of the droplet and the changing characteristics of the contact line motion under different strength of the step conditions.The results show that the time required for the droplet to pass through the chemically heterogeneous step depends on the strength of the step,and that the droplet deforms considerably during this process.(3)The algorithm is designed to quantify the forces,surface energy and internal momentum distribution of the droplet during sliding based on real-time flow field density distribution data.It is found that when the strength of the chemical heterogeneous step is small and the droplet can slide quickly across the junction line,the unbalanced Young’s force will prevent the contact line from moving forward.As the strength of the chemical heterostructure step increases,the droplet slides across the junction line at a slower rate and the unbalanced Young’s force becomes the driving force for the forward movement of the contact line at the front end of the droplet.The kinetic energy is converted to surface energy before the front contact line crosses the junction line.After the droplet crosses the junction line,the gravitational potential energy is converted into surface energy and kinetic energy.In summary,this paper provides an intimate study of the sliding behaviour of threedimensional droplets using the chemical potential lattice Boltzmann method.The results will advance the understanding of wetting phenomena,provide guidance for controlling droplet motion on surfaces and help inspire the design of functional patterned surfaces,promising to extend the lattice Boltzmann method for more applications in numerical simulations in the field of 3D fluid motion.