Turbulent drag reduction of a d-type rough wall boundary layer with longitudinal thin ribs placed within the traverse grooves

Abstract

In order to control the turbulent energy production and transport processes due to the coherent vortices associated with the bursting phenomenon in a d—type rough wall turbulent boundary layer, longitudinal thin ribs were placed within the transverse grooves with a suitable spanwise spacing. Direct measurement of the local skin friction coefficient evidently shows the effectiveness of drag reduction using the longitudinal ribs. Maximum drag reduction rate to the d—type rough wall flow and to the smooth wall flow are 10% and 3%, respectively. The drag reduction rate can be reasonably expressed in terms of the rib Reynolds number. Comparisons of some mean flow properties between the d—type rough wall flow with and without the longitudinal ribs provide evidence that the present passive control device also reduces the turbulent energy production rate.KeywordsTurbulent Boundary LayerDrag ReductionReynolds Shear StressSkin Friction CoefficientWall FlowThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.