LES-DPS of the effect of wall roughness on dispersed-phase transport in particle-laden turbulent channel flow

The influence of wall roughness on the properties of particle-laden turbulent channel flow is investigated using Large Eddy Simulation (LES) for the fluid and Discrete Particle Simulation (DPS) for the particulate phase. The influence of wall roughness is treated stochastically following the approach of Sommerfeld (1992) in which the impact angle of the particle is comprised of the particle trajectory angle and a stochastic component due to wall roughness. Particle-wall collisions are elastic and for each of the three Stokes numbers considered computations are performed with standard deviation of the distribution of "wall roughness angles" of 0 (smooth wall), 2.5 and 5 degrees. Simulation results show that for a given wall roughness angle and particle Stokes number the most pronounced effect of roughness is on the wall-normal component of the particle velocity, which can be substantially increased by roughness. While the streamwise particle velocity variance is also increased by roughness, the spanwise component of the particle velocity variance exhibits relatively little sensitivity to surface roughness. Turbulent transport of the particle velocity variance can be strongly affected by roughness and can also provide a mechanism for transport of the particle velocity variance across the channel.