Technical Papers and Presentations

Due to particle interactions, magnetic particles suspended in non-magnetic fields tend to form chains, clusters or columns under magnetic fields. The non-spherical magnetic particles in the suspension show different rheological properties compared to spherical particles. In this paper, we present a direct numerical method to study the dynamics of a pair of ellipsoidal particles in a quiescent flow under uniform magnetic fields. Magnetic fields around the particles are modelled with the Magnetic Fields, No Currents interface of the AC/DC Module in COMSOL Multiphysics^® simulation software (right side in Figure 1). Fluid-structure interaction (FSI) is modelled using the Laminar Flow interface of the CFD Module, the Solid Mechanics interface of the Structural Mechanics Module and Moving Mesh features. The Maxwell stress tensor computed from the magnetic fields works as boundary load on the particle surfaces. The Laminar Flow and Solid Mechanics interfaces are coupled to calculate particle trajectories which includes position and direction of the particles. The Moving Mesh interface is used to describe the deforming mesh at the particle-fluid boundaries. The effect of several important factors, including initial position and aspect ratio of the particles, particle-particle interaction and relative motion of the particles are investigated. It is shown that the particles spend much more time for the global reorientation than for the local magneto-orientation. The particles require more time to form a stable chain for a larger initial relative distance and angle between the two particles, and a larger particle aspect ratio. The results in this study provide a possible explanation for the fundamental mechanism of particle interactions in the experiment.