Structures in a Turbulent Boundary Layer
Drawn by the prospect of net drag reduction, the manipulation of turbulent boundary layers has attracted much attention. Many aspects of a turbulent boundary layer are relatively easy to alter (e.g., the boundary layer can be artificially thickened, the local skin-friction distribution can be altered, etc.). However, very few manipulation techniques have been shown to produce a net drag reduction. One successful manipulation technique involves suspending thin ribbons or airfoils in the outer portion of the boundary layer, either individually or in pairs. This device, known either by the acronym BLADE (Boundary Layer Alteration DEvice) or by the acronym LEBU (Large Eddy Break Up) device, was devised and first researched at the Illinois Institute of Technology)1 and at NASA Langley.2 The latter name derives from the proposed mechanism by which a net drag reduction is achieved and which will be justified in the following presentation. Summaries of the results obtained using BLADE type devices have been compiled by Anders,3 Mumford & Savill4 and Bandyopadhyay.5 We have investigated in detail the changes in the turbulent flat-plate boundary layer produced by a BLADE device. Presented here are the results showing the effect of manipulation on the coherent structures in the boundary layer. (For a complete account of this investigation, see Lynn.6) To isolate the effects of introducing a simple momentum defect, the effects of a wire device on the boundary layer were also investigated. The wire device, consisting of a wire replacing the ribbons, was chosen to have the same device drag as the optimized BLADE device. Wire devices have not been shown to produce net drag reductions.
KeywordsBoundary Layer Drag Reduction Integral Length Scale Spanwise Wavelength Wire Device
Unable to display preview. Download preview PDF.
- 1.CORKE, T.C., GUEZENNEC, Y. and NAGIB, H.M. 1979 Modification in drag of turbulent boundary layers resulting from manipulation of large structures presented at the AIAA Symposium on Viscous Drag Reduction, Dallas, Texas, AIAA-81–26508.Google Scholar
- 2.HEFNER, J.N., WEINSTEIN, L.M. and BUSHNELL, D.M. 1979 Large-eddy breakup scheme for turbulent viscous drag reduction, presented at the AIAA Symposium on Viscous Drag Reduction, Dallas, Texas, AIAA-81–26507.Google Scholar
- 3.ANDERS, J.B. and WATSON, R.D. 1985 Airfoil large-eddy breakup devices for turbulent drag reduction presented at the AIAA Shear Flow Control Conference, AIAA-85–0520.Google Scholar
- 4.MUMFORD, J.C. and SAVILL, A.M. 1984 Parametric studies of flat plate, turbulence manipulators including direct drag results and laser flow visualisation presented at the ASME Symposium on Turbulent and Laminar Boundary Layers, New Orleans, Louisiana.Google Scholar
- 5.BANDYOPADHYAY, P.R. 1986 Mean flow in turbulent boundary layers disturbed to alter skin friction J. Fluids Engineering 108, 127–40.Google Scholar
- 6.LYNN, T.B. 1987 Manipulation of the structure of a turbulent boundary layer Ph.D. Thesis, Yale University, New Haven, Connecticut, May.Google Scholar
- 7.BLACKWELDER, R.F. and KOVASZNAY, L.S.G. 1972 Time scales and correlations in a turbulent boundary layer Physics of Fluids 15, 1545–54.Google Scholar
- 8.FAVRE, A.J., GAVIGLIO, J.J. and DUMAS, R.J. 1957 Space-time double correlations and spectra in a turbulent boundary layer J. Fluid Mech. 2, 313–42.Google Scholar
- 9.FAVRE, A.J., GAVIGLIO, J.J. and DUMAS, R.J. 1957 Further space-time correlations of velocity in a turbulent boundary layer J. Fluid Mech. 2, 344–56.Google Scholar
- 10.HEAD, M.R. and BANDYOPADHYAY, P. 1981 New aspects of turbulent boundary-layer structure J. Fluid Mech. 107, 297–338.Google Scholar
- 11.TOWNSEND, A.A. 1979 Flow patterns of large eddies in a wake and in a boundary layer J. Fluid Mech. 95, 515–37.Google Scholar