AbstractsPhysics

Interaction of particles in a viscous fluid with a wall and with other particles is often observed in phenomena like sedimentation, erosion and filtration processes. With the increasing computational power there is now the possibility of simulating such particle-laden flows from a micro-scale perspective by direct application of no-slip/no-penetration boundary conditions at the particles’ surface. To model the collisions in a particle-laden flow in an realistic manner it is required to understand the dynamics of individual collisions. To investigate the relevant parameters describing particle-wall interactions, experiments of a spherical particle colliding with an oblique wall have been performed in both air and in water. The measurements were carried out with spherical steel and delrin particles with a radius of 4 and 5 millimeter. The particle dynamics has been investigated by video-capturing the particle’s motion (translation and rotation) and the collision with an inclined plate. Upon collision with a wall energy is dissipated due to the inelastic nature of the contact. Furthermore the particle may stick or slip at the surface depending on the tangential force during impact. Three parameters are used to describe the macroscopic behavior of the collision. The normal coefficient of restitution e_n quantifies the dissipated energy. The tangential coefficient of restitution e_t quantifies the change in the tangential velocity at the point of the particle that collides with the wall. Finally the Coulomb coefficient of sliding friction μ_f is a measure how easily the particle sticks to or slips over the collision plate. These three parameters are sufficient to describe the dynamics of a particle-wall collision in air (dry collision). In a viscous fluid (wet collisions) these parameters are subject to change due to lubrication, piezo-viscous and history-forces. Whether the particle bounces in the fluid depends on the impact Stokes number (St = 2/9 *ρ_s*R*U/μ ), the ratio between particle inertia and viscous forces. The three parameters will be determined using Walton’s collision model [Walton, 1993] and are compared to the results found in literature [Gondret et al., 2002; Joseph and Hunt, 2004]. Furthermore, the difference between normal collisions and the normal component of oblique collisions is investigated. The particle’s impact Stokes number, has been plotted against the ratio of the normal wet and normal dry coefficient of restitution and compared to the results found by Joseph et al. [2001] and the empirical fit of Legendre et al. [2006]. In agreement with the results from literature we found that the normal component of oblique collisions equals the the results of normal collisions under similar conditions. The results for oblique particle wall collisions in a viscous fluid presented in this thesis, add to the few data present in literature, by using a different setup. Since the results for both dry and wet collisions are in agreement with the data from literature, this work may be used as validation for… Advisors/Committee Members: Breugem, W.P., Costa, P., Poelma, C..