Multi-flexible fiber flows: A direct-forcing immersed boundary lattice-Boltzmann lattice-spring approach

We demonstrate that a lattice-Boltzmann lattice-spring method can be used to simulate a dynamic behavior of a suspension of a large number of flexible fibers in finite Reynolds number flows. In the method, lattice-Boltzmann equation is adopted to simulate fluid velocity and vorticity while lattice-spring model with three-body forces can be employed to model the bending deformation of solid bodies. In order to realize the non-slip boundary condition, a forcing term is simply calculated by using the Newtonian second law and imposed with an immersed boundary scheme. The method is validated by comparing the present results with experiments and existing theories and methods. Subsequently, the method is applied to simulate a dynamic process of flexible fibers settling on a static or moving screen/wire net while a fiber mat is simultaneously built over the screen and resists fluid flowing. The number of fibers, fiber density and flexibility, and ratio of the relative velocity of the screen/wire to fluid can be systematically varied at different levels. Their influences on drainage rate are computed and evaluated.