A front-tracking method for simulating interfacial flows with particles and soluble surfactants

Abstract

In this research, a three-dimensional model is proposed to simulate the behavior of particle-covered droplets that contain soluble surfactant. The model includes a full two-way coupling between surfactant transport and particle motion, with surfactant concentrations at the interface and in the bulk linked to the flow and motion of the interface by a convection-diffusion equation. A front-tracking method is used to track the interfacial flow, while a semi-resolved particle method is used to model the particles, accounting for various forces acting on them, such as the excluded volume force, the direct contact force and the hydrodynamic lubrication force. The model also includes a surfactant-dependent surface tension that can affect the particle-interface interactions. The model is validated against previous numerical data and a parametric study is performed to examine the delicate interplay between flow fields and interfaces associated with surfactant concentration and particle motion. The study then investigates the role of surfactants in the dynamics of a particle-covered droplet, focusing on their coupled influence on droplet deformation. In addition, it is observed that particles bridge colliding droplet interfaces and suppress fluid drainage from the gap, preventing droplet coalescence along with the interparticle repulsion force.