Direct numerical simulation of turbulent liquid–solid flow in a small-scale stirred tank

Abstract

Particle-resolved direct numerical simulation of a 4-baffled cylindrical stirred tank with a 6-pitched blade-turbine-downflow (PBTD) impeller was carried out for the first time to understand the hydrodynamic characteristics of its turbulent solid–liquid flow. The fluid-particle and fluid-wall interactions are numerically described by the immersed boundary method (IBM) with smeared and sharp interfaces jointly on a staggered Cartesian grid. The particle diameter is 1 mm, and the impeller rotation speed changes between 23.88 and 15.88 rev/s, resulting in the impeller Reynolds number at 7031 and 4676, respectively, belonging to medium turbulent regime. The average solid volume fraction ranged from 0 to 0.1. The effect of particle inertia was also investigated by changing the particle–fluid density ratio from 1.5 to 3.0. Analysis of the simulation results indicates turbulence suppression in the bulk region and particle-induced strengthening of the axial liquid circulation. The quasi-steady and unsteady drag is correlated to the relative turbulence intensity and the turbulence dissipation rate obtained from the simulation data, respectively.