Particle image velocimetry experiments and direct numerical simulations of solids suspension in transitional stirred tank flow

Solids suspension in a stirred tank with a down-pumping pitched-blade turbine impeller has been investigated by using particle image velocimetry (PIV) experiments as well as direct numerical simulations (DNS) with a lattice-Boltzmann (LB) method. The flow regime of this solid-liquid two-phase system is transitional with the impeller-based Reynolds numbers Re = 1334. The refractive index matching (RIM) method is applied in the experiments. The overall solids volume fractions are up to 8% in the experiments as well as in the simulations. The liquid flow fields around the particles are highly resolved in both experimental and simulated cases which makes it possible to investigate solid-liquid interactions in detail. The average distributions of the solids over the tank volume as predicted by the simulations are in good agreement with the experimental results. It is shown that the presence of particles reduces the average velocities as well as the turbulent fluctuation levels of the liquid in both the experiments and simulations although the reduction in the simulations is weaker as compared to in the experiments.