Research On Droplet Impact To Discrete Particle Based On A SPH-DEM Coupling Method

Droplet impact on discrete particle is not only a common phenomenon in nature and engineering field, but also a classical and complicated Multiphase flow problem of incompressible free surface flow, gas and discrete particle coupling effect. Research on this topic provides a new way to study the theory and numerical simulation, which is of great importance. The results have practical value and can be used in sediment incipient motion, soil erosion, riverbed evolution and geological disaster forecast.SPH model is setup to study droplet impact on the solid surface near a pore. Influences of viscosity, gravity and internal pressure on the spreading droplet over orifice are respectively studied. Result shows that the spreading changes to jet flow after the droplet reaching the orifice, the jet passed it rapidly and in rather short times few effect did gravity contribute. However, viscosity can induce the jet curving into orifice obviously. Besides that with the internal pressure and inertia effect, the jet bottom fluctuates regularly and results Hole Suction phenomenon. Through analyzing the pressure of vertical section of orifice edge, internal pressure plays a significant role to the droplet be absorbed into orifice and finally lead to splashing. The numerical results are in good agreement with experimental data.Van der Waals state equation is used for attractive stress of surface tension in SPH model. Besides that a modified Quintic kernel function is proposed to improve the stability of repulsive stress. Attractive stress in the model is calculated with different kernel function from repulsive stress to improve model’s instability. Surface tension algorithm presented in this paper is validated by simulating square droplet oscillation. The period of simulation and theoretical value are compared to calibrated tensile stress parameter of the van der Waals state equation. Droplet impact on hydrophobic surface in consideration of surface viscous shear stress is simulated. The numerical data and experimental result are compared to analyzing the influence of surface viscous shear stress and surface tension on droplet moving. Research shows that surface viscous shear stress plays a leading role in spreading stage and the viscosity coefficient value enlarges along with the growth of velocity. Surface tension provides retraction force during retraction stage and the frictional drag(surface viscous shear stress) of this stage is less than that of spreading stage.A solid surface wettability mechanism is presented to investigate the impacts of solid surface’s wettability on static contact angle of droplet. Then numerical study on the process of droplet impact on wettable solid surface is done. Research shows that: firstly, the static contact angle of the droplet decreases with the increase of wettability coefficient, wettability has little impact on the droplet’s spreading stage. Secondly, the effect of wettability to droplet’s movement characteristics is obvious in retraction and rebound stages. Thirdly, the wettability coefficient should be varied with saturation and stress fluctuation. The higher saturation is, the lower wettability coefficient would be, while the stress fluctuation goes the contrary.A new SPH-DEM coupling method aimed to studying the interaction between free surface flow and discrete particles is present. A SPH-DEM steering visual numerical system is set up based on mixed compiling principle. The interaction forces between fluid and discrete particles consists of three parts, which are repulsive force, viscous shear force and attractive force caused by capillary action. The simulation of droplet impact to discrete particles shows the coupling method’s applicability and the impacts of solid particles’ wettability on droplet’s motion. Beside that experiment study of droplet impact to discrete particles is also done.