Moderate-Reynolds-number flows in ordered and random arrays of spheres

Lattice-Boltzmann simulations are used to examine the effects of fluid iner tia, at moderate Reynolds numbers, on flows in simple cubic, face-centred c ubic and random arrays of spheres. The drag force on the spheres, and hence the permeability of the arrays, is calculated as a function of the Reynold s number at solid volume fractions up to the close-packed limits of the arr ays. At Reynolds numbers up to O(10(2)), the non-dimensional drag force has a more complex dependence on the Reynolds number and the solid volume frac tion than suggested by the well-known Ergun correlation, particularly at so lid volume fractions smaller than those that can be achieved in physical ex periments. However, good agreement is found between the simulations and Erg un's correlation at solid volume fractions approaching the close-packed lim it. For ordered arrays, the drag force is further complicated by its depend ence on the direction of the flow relative to the axes of the arrays, even though in the absence of fluid inertia the permeability is isotropic. Visua lizations of the flows are used to help interpret the numerical results. Fo r random arrays, the transition to unsteady flow and the effect of moderate Reynolds numbers on hydrodynamic dispersion are discussed.