A numerical analysis on the collision behavior of water droplets

Abstract

A series of numerical simulations on the droplet collision for various conditions of Weber number, impact parameter, and droplet size ratio are performed and compared with some experimental results and other theoretical predictions. Droplet collision behavior is normally divided into four categories: bouncing, coalescence, stretching separation, and reflexive separation. One of the important parameters associated with the collision outcome is the relative velocity of colliding droplets. The range of Reynolds number in this paper is between 500 and 4000. Therefore, main parameters that can influence the collision outcome are Weber number, droplet size ratio, and impact parameter. When two droplets merge, the overall surface area is decreased, resulting in reduced surface energy. Usually, reflexive separation occurs at a large Weber number and a small impact parameter. Using the relation between the kinetic energy and the surface energy of the nominal spherical droplet, they found theoretical prediction separating the reflexive separation region from the coalescence region. Stretching separation occurs when the region of overlap between two colliding droplets is small. VOF method is used for free surface tracking, in which, each phase is identified by using volume fraction.