The Study And Simulation Of The Movement Of Droplet Impacting On Superhydrophobic Wall

The phenomenon of spray droplet impacting onto the wall exists in many areas. In the working process of medium or small high-speed high pressure diesel engines and direct injection gasoline engines, the emergence of spray droplet impacting onto the wall is almost inevitable influenced by the geometry of the combustion chamber space. The physical process of fuel spray droplet impacting onto the wall influences the thermal efficiency and emission of engine directly. Though the research of a single droplet impacting the wall is the basis study, it is not very comprehensive for the study of liquid movements of droplet impacting onto the super hydrophobic wall. Single droplet impacting onto the surface was set as the research object in this thesis, and the liquid movements of droplet impacting onto the wall were researched. The fundamental research could be contributed to enriching the research contents of droplet impacting on the wall, and providing theoretical basis for the control technique of droplet impacting onto the wall.The hydrophilism of wall has great influence on the droplet changing process after impacting wall. This thesis established two-dimensional model of droplet impacting onto the wall firstly. Using this model and Fluent software, the liquid movements of droplet impacting onto hydrophilic wall obliquely was researched with the combined Level Set-VOF method of interface tracking. Based on research of the morphology changes of droplet impacting onto the super hydrophobic wall, the morphology of droplet under different initial condition was gained, such as spreading, breaking, and bouncing. Then this thesis analyzed how the different initial diameter and impacting velocity of the droplet effect movement of the droplet impacting onto the wall and summarized the reason why droplet bounces or breaks on the wall based on the analysis of the pressure field and velocity field. Also this thesis put forward the critical conditions of droplet bouncing or breaking after impacting onto the super hydrophobic wall vertically.As the second research contents of this thesis, the movement of droplet impacting onto the wall obliquely was researched. Through the analysis of droplet shape variations and characteristic parameter variations while droplets were spreading on the dry wall after impacting, this thesis got the regularity that how different initial conditions influence the spreading movement of droplet impacting onto the wall obliquely. The bubble entrainment forming process on the surface and that how the initial conditions and the hydrophilicity of wall surface influence the bubble forming were simulated and analyzed.Based on the above research contents, this thesis carried out the research of the movement of droplet impacting onto the super hydrophobic wall obliquely. The comparative analysis of the movement of droplet impacting super hydrophobic wall motion obliquely was done in this thesis. Based on the research of spreading and bouncing movement of droplets after impacting, this thesis presented the regularity that how different impacting angle and initial conditions influence spreading and bouncing movement of droplets after impacting, and analyzed the reason why bouncing phenomenon exists. As the research emphases, this thesis studied the regularity that how different impacting angle and initial conditions influence breaking movement of droplets after impacting, and analyzed the cause of breaking phenomenon. Also this thesis presented the critical conditions of droplet bouncing or breaking after impacting onto the super hydrophobic wall obliquely.Finally, this thesis researched the liquid film rupture phenomenon after droplet impacted the thin liquid layer on the surface of super hydrophobic wall. Based the analysis, this thesis concluded that with weakening of hydrophilicity of wall surface, liquid film rupture phenomenon is easier to occurs after droplet impacted thin liquid layer of the surface. How impacting velocity, initial diameter of droplet and the thickness of liquid film influence the liquid film rupture phenomenon after impacting was studied, and the causes of liquid membrane rupture phenomenon were further analyzed. Also, how impacting angle and initial conditions influence the liquid film rupture after impacting onto the wall obliquely was studied in this thesis.