Particle clustering due to hydrodynamic interactions

Dynamic simulations of an isotropic suspension of particles in a viscous gas are performed. The energy in the suspension decays with time as a result of viscous dissipation in the gas. The rate of viscous dissipation in sufficiently energetic suspensions, those with a high Stokes number, is consistent with the theory of Sangani et al. [J. Fluid Mech. 313, 309–341 (1996)] for homogeneous hard-sphere suspensions. As the suspension loses energy, the dissipation rate decreases dramatically and the particles cluster as indicated by the presence of many more near neighbors than would be found in a hard sphere distribution.