Droplet-driven particle motions in fluids studied using coupled lattice Boltzmann method

A numerical method for describing droplet-driven particle motion at low Weber numbers in fluids is proposed. A coupling strategy combining the Shan–Chen (SC) model and the smoothed profile method (SPM) is employed. The proposed scheme correctly resolves the momentum transfer between solid particles and fluid phases, while effectively controlling the wetting condition. An interaction zone where three phases coexist is introduced to solve the contradiction between the SC model and SPM (i.e. whether fluid particles are allowed at the solid nodes). In the interaction zone, partial solid particles are entrapped in the fluids owing to the coexistence of solid and fluid particles, causing solid particles to exchange momentum with fluid particles. Furthermore, the interaction forces between fluid and solid particles near the solid surface are considered at nodes near pure solid particles within this region. Based on the proposed scheme, the interactions between freely moving particles and freely moving droplets were investigated, along with the effects of wettability (Gads) and volume forces (Fp*) on particle–droplet interactions. When a liquid droplet comes into contact with a solid particle, the adhesion force between the droplet and the solid surface promotes the movement of solid particles toward the droplet. When a double emulsion comes into contact with solid particles, the adhesion force between the emulsion film and solid surface causes the double emulsion to break at the connecting point, and the volume force of the emulsion film Fd* causes the solid particles to penetrate the emulsion.