Studies of the Dynamics of Suspensions of Ellipsoidal Particles*

The dynamics of suspensions of prolate ellipsoidal solid particles in a small periodic domain is studied by fully resolved numerical simulations, for relatively modest Reynolds numbers and a density ratio of ten. After describing the numerical method briefly, we examine the effect of volume fraction as it is changed from two to ten percent. The results show a transition from flow dominated by the hydrodynamic interactions between the particles and the fluid, although modified by collisions, at low volume fractions, to flow dominated by collisions at higher volume fractions. At low volume fraction, most of the particles fall broadside-on whereas, at the highest volume fraction, their orientations are essentially random. The distribution of the particles with respect to each other, as measured by the probability distribution of nearest distance, on the other hand shows a nearly random distribution at low volume fractions but at high volume fractions there is more clustering than for a random distribution. Results for different shapes, including oblate ellipsoids and spheres, and different Reynolds numbers and density ratios, are also discussed. This rich dataset will help us determine how the forces on each particle depend on the local flow structure.