Numerical simulation of droplet characterized by Rolie–Poly model with finite extensibility passing through cylinder obstacles

Abstract

The deformation and rupture of viscoelastic droplet passing through cylinder obstacles in a microchannel are investigated using OpenFOAM. The constitute relationship of droplet is modeled by the Rolie–Poly model with finite extensibility, and the two-phase interface is tracked by the volume of fluid method. The effects of capillary number (Ca), the distance between cylinders (l1), relaxation time ratio (ξ), Weissenberg number (Wi), etc., on droplet deformation and rupture are mainly explored. When Ca decreases, the symmetry of droplet rupture changes and three behaviors of the droplet, i.e., symmetrical rupture, asymmetrical rupture, and non-rupture, can be captured. Further research shows that the stagnation area formed between cylinders is broken with the increase in l1, where the two sub-droplets merge again. Viscoelastic droplet with a smaller relaxation time ratio ξ is more likely to extend into thin and durable filament. Especially, when ξ=0.2, the filament will break many times during the stretching process. During above-mentioned two kinds of development, the normal stress difference develops obviously at the places, where the filament breaks or the sub-droplets combine together. This may imply that the normal stress difference facilitates the rupture and coalescence of droplets. In addition, with the increase in elasticity, the normal stress difference tends to develop at the phase interface.