Numerical simulation of channel flow with a rib-roughened wall

Turbulent channel flows where there are small two-dimensional rods of square cross-section regularly arranged along one wall, normal to the average flow, are simulated without using any model. The other wall is assumed to be at because of the limitations on computer memory. Sparsely distributed ribs modulate the flow near the wall substantially, but when the ribs are densely distributed the property of flat-wall flow is retained to a large extent. The scales of time and length used to normalize near-wall turbulence are normally wall scales based on total wall drag and viscosity. However, it is thought that these scales may not be adequate, in view of the modi cation of the turbulence generation mechanism. On the other hand, the flow in the layer away from the wall has been confirmed to be little affected by roughness, and scaled by total wall drag and the distance normalized by the channel half-width. It has also been confirmed that the property of turbulence away from the wall in the case of a at wall comes closer to that of the wall in rough-wall flow. In addition, the growth process of hairpin vortices is only slightly modified by wall roughness.