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

The influence of wall roughness on dispersed-phase properties of particle-laden turbulent channel flow is investigated using large eddy simulation (LES) for the fluid flow and discrete particle simulation (DPS) for the particulate phase. Gas–solid flows are considered for which the particle equation of motion includes the contribution from the drag force. The influence of wall roughness is treated stochastically in which the impact angle is comprised of the particle trajectory angle and a stochastic component due to wall roughness. Elastic particle–wall collisions are considered with surface roughness characterized in terms of the standard deviation of the distribution of wall roughness angles. Computations are performed for three Stokes numbers and standard deviations in the wall roughness angle of 0 (smooth wall), 2.5° and 5°. LES–DPS results show that for a given wall roughness angle and particle Stokes number the most pronounced effect is on the wall-normal component of the particle velocity, which can be substantially increased by roughness. While the streamwise particle velocity variance also increases, the spanwise particle fluctuating velocity exhibits relatively little sensitivity to surface roughness. In addition, LES/DPS results show that wall roughness increases turbulent transport of the wall-normal particle velocity variance, in turn providing a mechanism for elevation of the particle velocity fluctuations across the entire flow.