Abstract
The wall static pressure in the vicinity of drag reducing outer layer devices in flat wall turbulent boundary layers has been measured and compared with an inviscid theory. Symmetric and cambered airfoil devices have been examined at small angles of attack and very low chord Reynolds numbers. Airfoil devices impose a sequence of strong favorable and adverse pressure gradients on the boundary layer whose drag is to be reduced. At very small angles of attack (± 2°), this pressure field extends up to about three chord lengths downstream of the trailing edge of an airfoil device. Also examined are the pressures on the upper and lower surfaces of a symmetric airfoil device in the freestream and near the wall. The freestream pressure distribution around an airfoil section is altered by the wall proximity. The relevance of lift enhancement caused by wall proximity to drag reduction has been discussed. The pressure distributions on the flat wall beneath the symmetric airfoil devices are predicted well by the inviscid theory. However, the remaining pressure distributions are predicted only qualitatively, presumably because of strong viscous effects.
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Abbreviations
- C D :
-
coefficient of drag, D/(1/2 ϱ U 2∞ S)
- C DP :
-
coefficient of drag penalty, 2 (ϕ − θREF)/c
- c :
-
chord of an airfoil device
- C f :
-
coefficient of local skin friction {ie393-1}
- C L :
-
coefficient of lift L/(1/2 ϱ U S∞
- C p :
-
coefficient of pressure, L/(1/2 ϱ U 2 ∞ S)
- H :
-
shape factor of the boundary layer, δ*/ϕ
- D :
-
drag
- L :
-
lift
- p :
-
wall static pressure
- Re c :
-
Reynolds number, U ∞ c/v
- S :
-
device area
- U :
-
mean velocity along x-direction
- x :
-
longitudinal distance on the flat surface underneath a device or distance along airfoil chord from leading edge
- y :
-
distance normal to the flat wall (Fig. 1)
- α:
-
angle of attack
- β:
-
pressure gradient parameter, δ*/τ w dp/dx
- δ:
-
flat wall boundary-layer thickness
- δ* :
-
displacement thickness,{ie393-2}
- ϕ:
-
momentum thickness {ie393-3}
- ϱ:
-
density of the medium
- ϱ:
-
density of the medium
- τ w :
-
wall shear stress
- ν:
-
kinematic viscosity of the medium
- o :
-
longitudinal position of leading edge of device or pertaining to device in flat wall boundary layer
- DP :
-
drag penalty (equation 2)
- REF:
-
reference condition
- TE :
-
trailing edge of airfoil device
- ∞:
-
freestream condition
References
Anders, J. B. 1985: Low Reynolds number LEBU performance. Second ONR-NASA-AFOSR Workshop on Drag Reduction and Boundary Layer Control, National Academy of Sciences, Washington, DC, October 22–25, 1985 (Abstract only)
Anders, J. B.; Watson, R. D. 1985: Airfoil large-eddy breakup devices for turbulent drag reduction. Paper No. AIAA-85-0520
Bandyopadhyay, P. R. 1986a: Review — mean flow in turbulent boundary layers disturbed to alter skin friction. Trans. ASME J. Fluids Eng. 108, 127–140
Bandyopadhyay, P. R. 1986b: Drag reducing outer-layer devices in rough wall turbulent boundary layers. Exp. Fluids 4, 247–256
Bertelrud, A. 1984a: Full scale experiments into use of large-eddy-breakup devices for drag reduction on aircraft. AGARD CP-365
Bertelrud, A. 1984b: Use of profiled ribbons for drag reduction in flight. EUROMECH 181 Colloq. Saltsjobaden, Sweden (see also a report on EUROMECH 181, FFA TN 84-60)
Bushnell, D. M. 1983: Turbulent drag reduction for external flows. Paper No. AIAA-83-0227
Corke, T. C.; Nagib, H. M.; Guezennec, Y. G. 1982: A new view on origin, role and manipulation of large scales in turbulent boundary layers. NASA CR-165861
Doria, M. L.; South, J. C. Jr. 1982: Transonic potential flow and coordinate generation for bodies in a wind tunnel. Paper No. AIAA 82-0223
Ferguson, D. R.; Keith, J. S. 1975: Modification to the stream-tube curvature program, vol. 1: Program modifications and user's manual. NASA-CR-132705
Goodman, W. L. 1985: The effect of opposing-unsteady vorticity on the turbulent structures in wall flow. Paper No. AIAA 85-0550
Green, L. L. 1984 (private communication)
Hoerner, S. F.; Borst, H. V. 1975: Fluid-dynamic lift practical information on aerodynamic and hydrodynamic lift. Hoerner Fluid Dyn., Brick Town NJ, USA
Miley, S. J. 1982: A catalog of low Reynolds number airfoil data for wind turbine applications. Rep. No. RFP-3387, UC-60, Dept. Aero. Eng., Texas A & M University
Mueller, T. J. 1984: The influence of laminar separation and transition on low Reynolds number airfoil hysteresis. Paper No. AIAA 84-1617
Mumford, J. C.; Savill, A. M. 1984: Parametric studies of flat plate turbulence manipulators including direct drag results and laser flow visualization. In: Uram, E. M.; Weber, H. E. (eds.) Laminar turbulent boundary layers - ASME FED Vol. 11, pp. 41–51
Plesniak, M. W.; Nagib, H. M. 1985: Net drag reduction in turbulent boundary layers resulting from optimized manipulation. Paper No. AIAA 85-0518
Reidy, L. W. 1985: Turbulent boundary layer modification in high-speed water flow. Second ONR-NASA-AFOSR Workshop on Drag Reduction and Boundary Layer Control, National Academy of Sciences, Washington/DC, October 22–25, 1985 (Abstract only)
Sahlin, A.; Alfredsson, P. H.; Johansson, A. V. 1986: Direct drag measurements for a flat plate with passive boundary layer manipulators. Phys. Fluids 29, 696–700
Sreenivasan, K. R. 1985: On the mechanism of net drag reduction in turbulent boundary layers using blade manipulators. Second ONR-NASA-AFOSR Workshop on Drag Reduction and Boundary Layer Control, National Academy of Sciences, Washington/DC, October 22–25, 1985 (Abstract only)
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Bandyopadhyay, P.R., Watson, R.D. Pressure field due to drag reducing outer layer devices in turbulent boundary layers. Experiments in Fluids 5, 393–400 (1987). https://doi.org/10.1007/BF00264403
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DOI: https://doi.org/10.1007/BF00264403