Particle clustering due to hydrodynamic interactions

Dynamic simulations of an isotropic suspension of particles in a viscous ga s 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 suffi ciently energetic suspensions, those with a high Stokes number, is consiste nt with the theory of Sangani [J. Fluid Mech. 313, 309-341 (1996)] for homo geneous hard-sphere suspensions. As the suspension loses energy, the dissip ation rate decreases dramatically and the particles cluster as indicated by the presence of many more near neighbors than would be found in a hard sph ere distribution. (C) 2000 American Institute of Physics. [S1070-6631(00)01 805-5].