Effects of surface roughness in a turbulent plane Couette-Poiseuille flow

Abstract

Direct numerical simulations of a fully developed turbulent Couette-Poiseuille flow with a rod-roughened wall is performed to investigate effects of two-dimensional surface roughness elements at Re=7200, based on the centerline laminar velocity and channel half-height (h). The roughness elements are periodically arranged on the bottom wall with a streamwise pitch of λ=8k and the roughness height is k/h=0.12, where k is the roughness height. It is shown that the wall-normal and spanwise stresses and Reynolds shear stress are stronger for the rough wall Couette-Poiseuille flow than the Couette-Poiseuille flow due to the near-wall energy redistribution by the surface roughness. Interestingly, the Reynolds stresses for the rough wall Couette-Poiseuille flow are clearly shown to be decreased in the outer layer. The decrease of the turbulence activity in the channel core for the rough wall Couette-Poiseuille flow is due to the weakening effect of large-scale structures by the surface roughness.