A front-tracking lattice Boltzmann method to study flow-induced deformation of three-dimensional capsules

In this paper, a hybrid method is proposed to study the flow-induced deformation of three-dimensional capsules. The capsules consist of Newtonian liquid drops enclosed by thin elastic membranes. In the proposed approach, the front-tracking method is coupled with the lattice Boltzmann method. The fluids inside and outside the capsule is treated as one fluid with varying physical properties, and is modeled by the lattice Boltzmann equation. The capsule membrane is explicitly tracked by the membrane nodes that are advected by the flow. The multi-block strategy of the lattice Boltzmann method is employed to refine the mesh near the capsule, which greatly increase the accuracy and efficiency of the three-dimensional computation. The capsule membrane is discretized into unstructured flat triangular elements, and a finite element model is incorporated to account for the membrane mechanics. With the present method, the transient deformation of initially spherical capsules with membrane following Neo-Hookean constitutive laws is simulated in shear flow, under various dimensionless shear rates and ratios of internal to surrounding liquid viscosities. The present results, including the Taylor shape parameter, the capsule inclination angle and the tank-treading frequency, agree well with previously published numerical results.