Direct drag measurements in a turbulent flat-plate boundary layer with turbulence manipulators

• Published in: Experiments in fluids 1995-10, Vol.19 (6), p.405-416
• Main Authors: LYNN, T. B, BECHERT, D. W, GERICH, D. A
• Format: Article
• Language: English
• Subjects: Boundary layer and shear turbulence; Exact sciences and technology; Fluid dynamics; Fundamental areas of phenomenology (including applications); Physics; Turbulence control; Turbulent flows, convection, and heat transfer
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/BF00190258

The effect of turbulence manipulators on the turbulent boundary layer above a flat plate has been investigated. These turbulence manipulators are often referred to as Large Eddy Break Up (LEBU) devices. In particular, the trade-off between the drag of the turbulence manipulator and the drag reduction due to the shear-stress reduction on the flat plate downstream of the manipulator has been considered. The measurements were carried out with very accurate force balances for both the manipulator drag and the shear stress on the flat plate. As it turns out, no net drag reduction is found for a fairly large set of configurations. A single thin blade as a manipulator performed best, i.e., it was closest to break-even. However, a further improvement is unlikely, because the device drag of the thin blade elements used here has already been reduced to only that due to laminar skin friction, and is thus the minimum possible drag. Airfoils performed slightly worse, because their device drag was higher. (Author)