Suspension of flexible cylinders in laminar liquid flow

A methodology for particle-resolved simulation of dense suspensions of flexible cylindrical particles in Newtonian liquid flow is described. It is based on the Lattice–Boltzmann method for solving the liquid flow and an immersed boundary method for imposing no-slip at the particle surfaces and providing the distribution of liquid–solid interaction forces over the particle surfaces. These forces—along with contact forces—translate, rotate as well as bend the cylindrical particles. Verification tests have been performed for a single cylinder settling and deforming under gravity at a low Reynolds number. The method has been applied to a clamped flexible cylinder in microchannel flow for which experimental data are available. It then is used to investigate the behavior of hundreds of flexible cylinders with length over diameter aspect ratios of 4 and 6 in a container agitated by an impeller at a Reynolds number of 87 which implies laminar flow. The overall solids volume fraction is 15%. We study the effect of the bending stiffness of the particles on the solids suspension process, on the extent of particle deformation as well as on the torque required to spin the impeller.