Numerical Simulation Of Vertical Collisions Of Different Size Droplets On Superhydrophobic Wall

In order to study the dynamic process of droplets colliding on the superhydrophobic wall in the vertical direction,Numerical simulation is used to study the collisions between droplets with different diameters and superhydrophobic planes.Whether the droplet is bouncing and the impact of various dimensionless parameters during the collision are studied.Bounce contact time,spreading diameter and recovery factor are analyzedIn view of the above problems,The difference between the different working conditions was synthesized three major dimensionless parameters(Re?We?Oh)by the VOF method and the non-dimensionalized.We number stands for the ratio of inertial force to surface tension,Oh number represents the ratio of viscous force to surface tension,and ai represents the diameter ratio between different droplets.By comparing the dynamic processes under different dimensionless parameters,we can investigate the effect of gravity,viscous force and surface tension on the collision and bouncing of droplets.The results show that most conditions can bounce when large droplets collide with small droplets(ai ? 1).Bouncing conditions are divided into three situations.When We number is small,the initial phenomenon of "liquid bridge" is more obvious.When We number and Re number are larger,the phenomenon of "liquid bridge" is not obvious,the droplets are patted flat and shattered.When We number is larger and Re number is smaller than type b,the phenomenon of "liquid bridge" is not obvious and the droplets are patted flat but not broken.Non-bouncing conditions are divided into two situations.When Oh number is particularly small,some droplets can not bounce,because the impact of gravity is too large.When Oh number is particularly large,viscous force has a great influence,and droplets can not bounce because of excessive adhesive loss.Collision mode will change when small droplets collide with large droplets(ai>1).Fluctuations are produced after the droplets are fused.It can drive the fusion droplets to collide with the wall and rebound.As ai increases,there is a substantial increase in conditions that can not be bounced.In addition to gravity and sticky factors that can cause droplets to fail to pop,Sometimes the droplets can not bounce because of the smaller We number.Droplet deformation is small after the collision,and its wave transmission is weak.So it can not drive the droplets to bounce.The We number has a major effect on the droplet collision process.The maximum spreading diameter and contact time increase with the increasing of We number.The maximum spreading diameter is approximately proportional to We0.2 The contact time is approximately proportional to We0.5.However,the fitting coefficient in front of We will increase with the increasing of ai.Re number will have a certain impact on the drop collision.After the droplets collide and fuse,the recovery coefficient is mainly affected by the degree of deformation,viscous loss and gravity factors.