Suspension flow and sedimentation in self-affine fractures

Abstract

The transport and gravitational sedimentation of a particulate suspension in fracture joints with self-affinely rough walls is studied by lattice Boltzmann numerical simulations. We consider either homogeneous or bidisperse distributions of non-Brownian spheres in a Newtonian fluid, driven through a fracture by a pressure gradient, and acted upon by gravity. Most results concern the case of open fractures, in which the two walls of the channel do not approach closely enough to block the flow. We present profiles of particle density and profiles of particle and fluid velocities, along with total flow rates and characterizations of the sediment, for three values of particle concentration and a range of buoyancy and Reynolds numbers, principally in the inertial regime. We systematically study the effects of increasing the pressure gradient and the strength of sedimentation and compare the results to those for channel bounded by flat surfaces. We find that both the flow rate and the average particle velocity for flows through an open fracture, when suitably normalized, depend only on the volume fraction of the particles and the buoyancy number in the steady state regardless of the pressure drop, and observe interesting scaling laws in the large buoyancy number limit. We also investigate the possibility for correlations between the surface morphology of the sediment region and the geometry of the underlying fracture surface in the strong sedimentation limit, but no evidence for correlation is found.