Abstract
Based on a model for momentum transport and turbulence production near the wall by means of unsteady streamwise vortex, a turbulence control technique with longitudinal thin ribs were proposed for d-type rough wall boundary layer and an experiment with direct skin-friction measurement confirmed its efficiency for turbulent drag reduction. The maximum reduction rates of local skin friction coefficient compared with the original d-type rough wall flow and a smooth wall flows are about 10% and 3%, respectively. Examination of the turbulent intensity and Reynolds shear stress profiles shows that the vortex model assumed for the present control technique is reasonable. The streaky structure was observed near the wall and effect of the longitudinal thin ribs onthe probability density distribution of the spanwise spacing λz was investigated.
