Hydrodynamic screening in sedimenting suspensions of non-Brownian spheres

It has been suggested [D. L. Koch and E. S. G. Shaqfeh, J. Fluid Mech. 224, 275 (1991)] that the long-range hydrodynamic interactions in sedimenting suspensions of non-Brownian spheres are screened by changes in the pair correlation function. However, a large-scale numerical simulation, using more than 32000 spheres, with full many-body hydrodynamic interactions, has found no evidence of the predicted changes in suspension microstructure. The absence of hydrodynamic screening in the simulations is shown to lead to divergent velocity fluctuations, in disagreement with recent experimental results [H. Nicolai and E. Guazzelli, Phys. Fluids 7, 3 (1995)].