  In this paper the capabilities of the turbulence-resolving Eulerian-Eulerian
two-phase flow model to predict the suspension of mono-dispersed finite-sized
solid particles in a boundary layer flow are investigated. For
heavier-than-fluid particles, having settling velocity of the order of the bed
friction velocity, the two-fluid model significantly under-estimates the
turbulent dispersion of particles. It is hypothesized that finite-size effects
are important and a correction model for the drag law is proposed. This model
is based on the assumption that the turbulent flow scales larger than the
particle diameter will contribute to the resolved relative velocity between the
two phases, whereas eddies smaller than the particle diameter will have two
effects: (i) they will reduce the particle response time by adding a
sub-particle scale eddy viscosity to the drag coefficient, and (ii) they will
contribute to increase the production of granular temperature. Integrating
finite-size effects allows us to quantitatively predict the concentration
profile for heavier-than-fluid particles without any tuning parameter. The
proposed modification of the two-fluid model extends its range of applicability
to tackle particles having a size belonging to the inertial range of turbulence
and allows us to envision more complex applications in terms of flow forcing
conditions, i.e. sheet flow, wave-driven transport, turbidity currents and/or
flow geometries, i.e. ripples, dunes, scour.
