Large Eddy Simulation of particle-laden flow over dunes

The particle-laden turbulent flow over a two-dimensional dune bathymetry is studied by means of Large Eddy Simulation (LES). The 4-way coupling regime for particle–particle and particle-flow interactions is applied and an appropriate empirical formula is used to estimate the bedload transport. The flow conditions correspond to river flow in laboratory scale at a Reynolds number equal to 17 , 500 with respect to the maximum water depth and bulk velocity. The dune-shaped bed is introduced within a Cartesian grid by means of the Immersed Boundary Method. A particle cloud consisting of spherical particles is released within the carrier fluid under the influence of the Stokes drag and gravity forces. Three different types of particles are examined: acrylic, glass and steel particles. The particle volume fraction is significant and a hard-sphere model is deployed to account for particle–particle collisions in a 4-way coupling regime. Closure parameters for the collision model have been adopted for each type of the examined particles, based on experimental works in literature. Results focus on the effect of the particle inertia on their kinematics, the velocity field and the shear stress along the dune bed which modifies bedload transport. Using the numerical simulations presented, it can be observed that when larger particle-to-fluid density ratios were examined, larger slip velocities between the fluid and particle phases were recorded.