Numerical simulation of the collision behaviors of binary unequal-sized droplets at high Weber number

Abstract

In the spray combustion process, the distribution of droplet size and velocity will affect the atomization performance of the fuel and the combustion effect. Compared with binary equal-sized droplet collisions, binary unequal-sized droplet collisions are more in line with the actual situation. In this paper, a numerical investigation of binary unequal-sized droplet collision has been performed under different high Weber numbers (from 210 to 810) and impact parameters (B ≈ 0.3–0.9) by a coupled level-set and volume of fluid method with adaptive mesh refinement technology. Unlike the coalescence and separation phenomena at low and medium Weber numbers, at high Weber numbers, due to the difference in velocity between large and small droplets, the rim expands radially outward in different ways and further breaks up. The splashing behavior of the droplets can also be observed. As the Weber number increases, the breakup moment of the droplets advances and the maximum radial deformation diameter increases first (We = 210–360) and then decreases (We = 360–810). By changing the impact parameters, it can be found that binary off-center collisions are associated with rotational motion. At larger impact parameters, the features of the capillary wave instability can be observed on the surface of the ligament.