中空液滴倾斜撞击水平液膜的动力学数值研究

Numerical study on dynamics of oblique hollow droplet impact on a liquid film

近年来,中空液滴因其在热喷涂、发泡材料的三维打印技术等领域中的优势再次引发了人们的关注.本文基于流体体积分数法(VOF)对中空液滴倾斜撞击水平液膜的动力学特征进行了数值计算,探究了不同撞击条件下中空气液滴倾斜撞击液膜后水花的形成以及演化过程,并分别对撞击倾角、液膜厚度以及撞击速度的影响进行了分析.结果表明,随着撞击倾角的增加,两侧冠半径呈现相反的变化趋势;当液膜厚度增加时,存在一个临界液膜厚度,此时右冠高度达到最大值;当撞击速度增大时,中空液滴倾斜撞击后的流动现象产生由无水花到有水花再到冠状水花的转变.当撞击速度达到一定值时,液滴前进方向一侧液膜不稳定性增强,并导致该侧的冠更容易在撞击初期发生破碎断裂.此外,本文还讨论了不同撞击条件下液滴内气泡的变形过程,并对不同条件下中空液滴倾斜撞击液膜后的水花形态进行了总结.

Recently,there has been renewed interest in hollow droplets impaction since its great significance for thermal spraying,the threedimensional(3D)printing of foam material.In the present study,we numerically study the dynamic characteristics of a hollow droplet obliquely impacting the liquid film via the volume of fluid(VOF)method.The splash formation and evolution during the oblique hollow droplet impact process under different conditions are investigated.The impact angle,film thickness,and impact velocity influences are analyzed.The results demonstrate that,with the impact angle increasing,the variation trends of the crown radius on both sides are opposite.When the film thickness increases,there is a critical film thickness at which the right crown height reaches the maximum.The increasing impact velocity leads to a flow phenomenon transition from non-splashing to splashing and even to a crown.When the impact velocity reaches a certain value,the liquid film on the front side will become unsteady,which makes the crown on this side prone to rupture at the early stage of impact.The bubble deformation during the impact process under different conditions is also discussed,and the patterns of the splashing behaviour under different initial conditions are summarized.