Simulation investigation of two droplets vertically impacting on solid surface simultaneously

Abstract

The flow characteristic of the droplets impacting on solid surface is extremely significant for practical engineering applications. The problem is also very complicated since there are many parameters that may influence the process of droplets impacting on a solid surface. Therefore the numerical study of behaviors of droplets impacting on a solid surface is performed in this work. With a given impact velocity, two two-dimensional axisymmetric droplets subsequently interact on the solid surface. To conduct numerical simulations, a mass conserved level set method is adopted, and the gravity and surface tension are taken into consideration in the process of droplet development on the solid surface. The effects of Weber number, surface contact angle, the horizontal distance between the two droplets, and droplet arrangement on the dynamic behaviors of droplet impact are systematically investigated. It is found that two droplets vertically impacting on solid surface simultaneously can produce a columnar liquid jet column, and the horizontally spreading liquid on the solid surface will break up in several segments as time goes by. With the increase of Weber number, the secondary droplets are generated from liquid jet, and the columnar liquid jet rebounds away from the surface subsequently. If the Reynolds number, surface contact angle and the horizontal distance are set to be, respectively, 2000, 90°and 2, in particular, the non-dimensional length of liquid spread is unrelated to Weber number when the non-dimensional time TT>2. Meanwhile, the dynamic change characteristics of the non-dimensional liquid jet height are about the same during the jet rising, but the jet falling time becomes shorter as the Weber number decreases. Obviously, the bigger the Weber number, the bigger the biggest non-dimensional height of liquid jet and length of liquid spread are. On the other hand, with the increase of surface contact angle, the columnar liquid jet rebounds away from the surface and the spreading liquid breaks up much earlier on the surface. Also, the non-dimensional height of liquid jet and length of liquid spread grow with the increase of surface contact angle. In addition, in the case that the Weber number, Reynolds number and surface contact angle are set to be 32, 2000 and 90° respectively, we also find that the correlation between the biggest non-dimensional jet height and horizontal distance is not monotonic. Under the circumstances, the biggest non-dimensional height of liquid jet is achieved when the distance is set to be 2, and the phenomenon of liquid jet rebound occurs subsequently, whether the rebound phenomenon of the jet liquid column is related to the horizontal distance of the droplet or not. And finally, as the horizontal distance between the two droplets increases from 1.5 to 3, the non-dimensional length of liquid spread gradually increases.