Agitating cylindrical particles in laminar liquid flow

Three-dimensional, time-dependent simulations of dense agitated solid-liquid suspensions involving particles of cylindrical shape in a Newtonian liquid have been performed. The liquid flow is resolved by the lattice-Boltzmann method at length scales finer than the size of the particles, which implies particle-resolved simulations. The flow solution includes the hydrodynamic forces and moments on each particle that are used to integrate their linear and rotational equations of motion. No-slip at the particle surfaces is imposed by an immersed boundary method (IBM). The marker points of the IBM are also used to detect and carry out collisions between particles. This numerical procedure has been applied to systems contained in a rectangular box and agitated by a revolving disk as well as by a pitched-blade turbine with an impeller-based Reynolds number of 87, which indicates laminar flow. The overall solids volume fraction has been fixed to 15%; the number of particles is of the order of one thousand. We study the effect of impeller type and particle shape (in terms of the length over diameter ratio of the cylinders that has been varied between 1 and 4) on the extent to which the solids are suspended and on the way the cylinders orient themselves.