Axisymmetric Simulation of Viscoelastic Filament Thinning and Laser-Induced Forward Transfer with the Oldroyd-B Model

A fundamental understanding of the filament thinning of viscoelastic fluids is important in practical applications such as spraying and printing of complex materials. Here, we present direct numerical simulations of the two-phase axisymmetric momentum equations using the volume-of-fluid technique for interface tracking and the log-conformation transformation to solve the viscoelastic constitutive equation. The numerical results for the filament thinning are in excellent agreement with the theoretical description developed with a slender body approximation. We show that the off-diagonal stress component of the polymeric stress tensor is important and should not be neglected when investigating the later stages of filament thinning. In addition, we use this numerical model to simulate the blister-actuated laser-induced forward transfer process, which is a nozzle-less laser-based printing technique. We reveal the effect of viscoelasticity on the ejected droplet size, derive criteria for optimum printing conditions, and compare the numerical results with experiments.