Abstract
Particle-resolved, three-dimensional, time-dependent simulations of rigid and flexible cylinders fluidized by a liquid flow in fully periodic domains have been performed by means of the lattice-Boltzmann method supplemented with immersed boundaries. The solids volume fraction ranges from 0.10 to 0.48 and the length-over-diameter aspect ratio of the cylinders from 4 to 12. The bending stiffness of the cylinders is the third major input parameter. The resulting Reynolds numbers based on the average slip velocity of the cylinders and their equivalent diameter range from 6 to 70. It is shown that increasing the flexibility—that is, decreasing the bending stiffness—reduces the Reynolds number, an effect that is most pronounced for low solids volume fractions and long cylinders. As for rigid cylinders, the distribution of the orientation relative to the direction of gravity of the flexible cylinders is a pronounced function of the solids volume fraction and the aspect ratio. Flexibility tends to somewhat randomize the orientation distribution, which could explain the effect of flexibility on the slip velocity and thus the Reynolds number.
Highlights
Fiber suspensions are encountered in a number of process engineering applications
In recent papers [7,8,9], we have reported on particle-resolved simulations of inertial fiber suspensions where we solve for the flow dynamics through the lattice-Boltzmann (LB) method and impose no-slip conditions at the fiber surfaces by applying the immersed boundary method
The snapshots are taken after the system has reached a dynamic steady state
Summary
Fiber suspensions are encountered in a number of process engineering applications. In order to characterize them, one needs an extensive number of parameters and properties such as the fiber volume fraction, the size distribution of the fibers as well as their mechanical and surface properties. In principle, all these have an impact on the processability of the suspensions. We make an attempt to quantify fiber suspension flow by means of numerical simulation. The main fiber properties we consider in the simulations are their shape that we quantify as the length over diameter aspect ratio and their bending stiffness. The continuous-phase fluid the fibers are suspended in is assumed to be a Newtonian liquid
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