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Abstract Due to the special structure of surface and material properties, solid wall always shows adsorption of water at the interface, and this feature is particularly evident to small water droplets. Surface wettability is used to reflect the magnitude of adsorption force. A Lagrange wettable solid surface boundary condition is presented. It is assumed that the hydrophilia and capillary action of solid wall particles are unified as an adsorption force acting on the liquid particles of supported domains. The adsorption force is deemed relevant to fluid pressure, saturation and surface hydrophilia. To investigate the adsorption phenomenon, several interactions between single droplet and wettable solid surface are simulated by a stress-correction Smoothed Particle Hydrodynamics (SPH) model. First, deformation processes of static droplets on different wettable solid surfaces are simulated to rate the relationship between the droplet’s static contact angle and the wettability coefficient. Then, droplet impact on wettable solid surface is studied to investigate the influence of wettability on the deformation of droplet. Finally, the propagation of stress wave on solid surface during the deformation is analyzed. Droplet’s impacting movement is divided into four stages: collision, spreading, retraction and rebound. Research shows that: according to the changing characteristics of droplet’s static contact angle, the mentioned boundary condition can clearly reflect the wettability of solid surface. Simulation of droplet impact on wettable solid surface shows good agreement with the experimental result. During the rebound stage, a sufficiently large wettability will cause droplet to deform into liquid column. The pressure wave of solid surface propagates and decays along with the spreading and retraction of droplet. Only at the end of the rebound stage, when the droplet is about to detach from the solid surface, tension plays a leading role. For the rest of time, the solid surface is under pressure. The study has improved the theory of interaction between free surface fluid and solid surface, which provides a reference for further study on the effects of free surface fluid and granular materials.
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Received: 08 June 2017
Published: 12 April 2018
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2018, Vol. 39 
