Fluid Force Acting on a Particle Falling toward a Wall

Abstract

A direct simulation of the falling motion of an immersed solid particle toward a wall is performed to investigate the mechanics of hydrodynamic collision of particles. The time-dependent boundary-fitted coordinate system is applied to the calculation of fluid flow around solid bodies. The fluid force acting on the particle is calculated by integrating the surface stress without any models. The obtained particle motion is compared with the corresponding experiment and theoretical analysis. The results of the numerical simulation, the experiment and the analysis using theoretical models agree quantitatively with respect to the falling motion of the particle. When the particle falls toward the wall, fluid force due to the squeeze of fluid in the gap is increased and prevents the particle from approaching the wall. As a result, the particle is decelerated and the fluid force caused by the unsteady motion of the particle is significantly increased. The numerical results reveal that the total fluid force acting on the particle can be explained by the sum of steady and unsteady fluid forces.