Direct Numerical Simulation of Sediment Transport in Turbulent Open Channel Flow

Direct numerical simulations of interface-resolved sediment transport in horizontal open-channel flow are currently being performed on the XC-4000. The channel bottom boundary is roughened with a fixed layer of spheres and about 9000 particles are allowed to move within the computational domain. The density ratio of the solid and fluid phase is 1.7 and the bulk Reynolds number of the flow is 2880. In the present configuration, the particles tend to accumulate near the bed because of gravity, but due to the turbulent motions, a cycle of resuspension and deposition is produced. This leads to a particle concentration profile which decreases with the distance from the bed. The preliminary results show that the presence of particles strongly modifies the mean fluid velocity and turbulent fluctuation profiles. The dispersed phase lags the carrier phase on average across the whole channel height. Both observations confirm previous experimental evidence. The different observations suggest that particle inertia, finite-size and finite-Reynolds effects together with gravity play an important role in this flow configuration. Several potential mechanisms of turbulence-particle interaction are discussed.