Computational simulation of fiber suspension in single and multiphase flow

Particle-level numerical methods have been used (Wu and Aidun, JFM 2010) for direct simulation of flexible fiber suspensions in shear flow based on the lattice-Boltzmann (LB) method with external boundary force (EBF). In this method, the flow is computed on a fixed regular ‘lattice’ using the lattice Boltzmann method, where each solid particle, or fiber in this case, is mapped onto a Lagrangian frame moving continuously through the domain. The LB-EBF method works well as long as the fiber length scale is comparable to the LB unit scale.  In many industrial applications, such as paper forming, this is not the case. Also, the suspension could include fine particles and capsules that are freely suspended and may interact with the fibers. A more computationally efficient method is developed based on analyzing the motion of fiber by Langevin Dynamics (LD) simulation of beads connected by a FENE spring.  In this study, we have coupled the LD analysis of each fiber with the LB fluid. This method allows analysis of fiber suspension in practical industrial applications with laminar or turbulent flow. Furthermore, it is now possible to include particles and capsules in the fluid. We show that this approach provides a practical tool for analysis of many industrial applications.