Numerical Study On Impact Dynamic Process Of Viscoelastic Droplet

The impacts of viscoelastic drop are a key element of a wide variety of phenomena encountered in nature,daily life and industrial processes.The research on mechanism and control technology of the phenomena is important in science and application.The impact dynamics of viscoelastic droplets presents highly nonlinear features,due to the coupling effects of various factors,such as moving contact line,phase interface topology change,surface stress effect and viscoelastic rheological property.It is difficult to study such phenomena by means of theory and experiment,constrained by the lack of the understanding of physical nature and the undeveloped experimental techniques.Therefore,in order to explore the physical mechanisms and realize control of droplets,relating numerical methods are needed.In this thesis,two numerical methods are developed to study the impacting phenomena of viscoelastic droplets,including viscoelastic two-phase flow numerical modal considering dynamic wetting effect and viscoelastic ternary phase flow numerical modal.And the relating programs were implemented in the open-source platform OpenFOAM?.And a serial of simulation on the impacting dynamics of viscoelastic droplets was conducted basing on the developed modals.The main works and relevant conclusions of this thesis are summarized as follow:(1)Based on two component Phase Field,Oldroyd-B viscoelastic constitutive model and dynamic wetting modal,the viscoelastic two-phase flow modal capable of describing dynamic wetting effect was established.The developed model overcomes the stress singularity problem of moving contact line and accurately describes the dynamic change of contact angle.(2)Based on the numerical simulation of the dynamic process of viscoelastic droplet impacting on solid wall,the effect of various properties of viscoelastic droplet on impact phenomena was investigated.The result showed,The elastic effect of the viscoelastic droplets promotes the spreading and retraction of the impact,and the normal stress difference mainly occurs in the vicinity of the contact line and the axis symmetry.(3)Based on three-component Phase Field method,combined with continuum surface stress modal and the Oldroyd-B modal,viscoelastic three-phase flow numerical modal was established.The model is capable to accurately describe the coupling effect of the three-phase interface deformation and its surface stress,and the use of continuous interface force model ensures the stability of numerical calculations.(4)The dynamic process of the viscoelastic droplets impacting on the liquid surface is numerically simulated.The temporal evolution of the droplet deformation and the normal stress difference distribution during the process and the influence of properties on the flow system are explored.The results show that the viscoelastic properties of the viscoelastic droplets have an important influence on the impact process of the droplets.The elastic effect promotes the spreading and deformation of the droplets,but the equilibrium is only related to the balances of the surface tension and gravity.