Direct numerical simulation of binary off-center collisions of shear thinning droplets at high Weber numbers

Abstract

Binary droplet collisions, a prototype elementary subprocess inside sprays, are investigated by direct numerical simulations (DNS) based on an extended volume of fluid method. We focus on shear-thinning droplet collisions. In order to capture the dynamics of droplet collisions with different outcomes, we account for off-center collisions at high Weber numbers. Such collision conditions lead to the formation of extremely thin fluid lamellae. It turns out that these thin lamellae determine the smallest length scales which must be resolved in a DNS. A stabilization algorithm is presented which prevents the lamellae from rupturing. It is validated by comparison with experimental data and applied for a droplet collision study of shear-thinning liquids. The results show that, independent of the off-set of the colliding droplets, a collision of Newtonian liquid droplets with appropriately chosen viscosity can reproduce the collision dynamics of the shear-thinning liquid droplets. This includes temporal evolution of shapes and energy.