DNS of turbulent flow in a square duct roughened by longitudinal ribs

Turbulent flow through a longitudinally-rib-roughened square duct is studied using direct numerical simulation (DNS). To understand the rib effects on the velocity field, DNS of a smooth-wall duct flow is also performed which serves as a baseline case of comparison. The impacts of longitudinal ribs on the flow structures, statistical moments of the velocity field and turbulence kinetic energy budget balance are investigated. It is interesting to observe tertiary vortex structures, which significantly alter the distributions of viscous and turbulent stresses within a longitudinally-rib-roughened square duct.