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  • 1
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    Planar Rayleigh scattering results in helium-air mixing experiments in a Mach-6 wind tunnel (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Planar Rayleigh scattering measurements with an argon-fluoride excimer laser are performed to investigate helium mixing into air at supersonic speeds. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment is demonstrated in a large-scale, Mach-6 facility. The detection limit obtained with the present setup indicates that planar, quantitative measurements of density can be made over a large cross-sectional area (5 cm x 10 cm) of the flow field in the absence of clusters.
    Keywords: OPTICS
    Type: Applied Optics (ISSN 0003-6935); 31; 30; p. 6529-6534.
    Format: text
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  • 2
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    Outer-layer manipulators for turbulent drag reduction (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The last ten years have yielded intriguing research results on aerodynamic boundary outer-layer manipulators as local skin friction reduction devices at low Reynolds numbers; net drag reduction device systems for entire aerodynamic configurations are nevertheless noted to remain elusive. Evidence has emerged for dramatic alterations of the structure of a turbulent boundary layer which persist for long distances downstream and reduce wall shear as a results of any one of several theoretically possible mechanisms. Reduced effectiveness at high Reynolds numbers may, however, limit the applicability of outer-layer manipulators to practical aircraft drag reduction.
    Keywords: AERODYNAMICS
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  • 3
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    Boundary layer manipulators at high Reynolds numbers (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Airfoil large-eddy breakup (LEBU) devices were tested on an axisymmetric body in the Langley Two Tank up to speeds of 50 ft/sec. NACA-0009, NACA-2412, E-193, and Clark Y contours were tested in single and tandem configurations. At the higher Reynolds numbers local skin friction downstream of the devices showed minimal reductions O (10 percent) and total body drag was increased 1 to 3 percent. At lower Reynolds numbers skin-friction reductions as large as 25 percent were measured and total body drag tended toward net reductions. The loss of effectiveness with increasing Reynolds number of conventional, outer layer devices suggests a decoupling of the outer and inner scales in high Reynolds number turbulent boundary layers.
    Keywords: AERODYNAMICS
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  • 4
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    Airfoil large eddy breakup devices for turbulent drag reduction (1986)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: It was determined from the present LaRC experiments that tandem, airfoil-shaped large eddy breakup (LEBU) devices can reduce local skin friction as much as 30 percent with a recovery region extending more than 100 boundary layer thicknesses downstream. These airfoils experience near laminar skin friction device drag and produce net drag reductions of up to 7 percent. In contrast to the thin plates used in previous experiments, these airfoils are more than 1000 time stiffer and hence have the potential to withstand the real flight environment (dynamic pressure 36 times larger than in low-speed wing tunnels). In addition, the higher Reynolds numbers of the present tests indicate drag reduction performance is at least as good (or better) as at lower Reynolds numbers.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Langley Symposium on Aerodynamics, Volume 1; p 573-585
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  • 5
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    Turbulent drag reduction research (1984)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Research in the area of turbulent drag reduction for attached flows is summarized. The most promising passive techniques utilize non-planar geometry. Of particular interest is the suitability of these devices for retrofit of existing vehicles. Five methods for reducing turbulent skin friction drag on bodies/fuselages are discussed. They are: (1) large-eddy breakup devices; (2) riblets; (3) slot injection optimization; (4) control of Emmons spot generation; and (5) relaminarization through massive suction. Except for the Emmons spot work these methods all indicate the possibility of sizable net reductions in skin friction for laboratory conditions.
    Keywords: AERODYNAMICS
    Type: AGARD Improvement of Aerodynamic Performance Through Boundary Layer Control and High Lift Systems; 13 p
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  • 6
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    Planar Rayleigh Scattering Results in Helium/Air Mixing Experiments in a Mach 6 Wind Tunnel (1991)
    In:  CASI
    Details
    Publication Date: 2018-06-02
    Description: Planar Rayleigh scattering measurements using an ArF-excimer laser have been performed to investigate helium mixing into air at supersonic speeds. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment is demonstrated in a large-scale, Mach 6facility. The detection limit obtained with the present setup indicates that planar, quantitative measurements of density can be made over a large cross sectional area (5 cm by 10 cm) of the flow field in the absence of clusters.
    Keywords: Lasers and Masers
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  • 7
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    Performance of large-eddy breakup devices at post-transitional Reynolds numbers (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Large-eddy alteration techniques were used to modify the drag characteristics of the turbulent boundary layer. Local skin-friction coefficients were measured for single and multi-element arrays of thin plates suspended in a fully turbulent, flat plate, boundary layer at R(theta) = 3,000. Effects of these devices were measured more than 300 boundary-layer thicknesses downstream to R(theta) = 17,000. It was found that although most of the devices reduced the local skin friction immediately downstream, this reduced skin-friction region persisted for only 100-120 delta-0, after which a rapid rise in skin-friction coefficient occurred, often exceeding flat plate values. Net drag reductions were obtained only for tandem configurations and these reductions were sensitive to device spacing and height. The maximum net drag reduction reported was approximately 7 percent with a device spacing of 10 delta-0 at a height of 0.8 delta-0.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 84-0345
    Format: text
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  • 8
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    Airfoil large-eddy breakup devices for turbulent drag reduction (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Large-eddy breakup devices were tested in a turbulent boundary layer at a momentum thickness Reynolds number of 7400. The drag reducing characteristics of thin, tapered plates, NACA 0009, and NACA 4409 airfoil shapes were determined and compared with lower Reynolds number data obtained with thin elements. The results indicate that at the higher Reynolds numbers of the present tests the thin, tapered plates in a tandem arrangement produced large downstream skin-friction reductions (maximum 0/40 percent/), and gave net drag reductions at least as large as for lower Reynolds numbers. Tandem NACA 0009 airfoils, which were approximately 10 times thicker than the thin plates, gave similar results with a maximum downstream skin-friction reduction of 0(30 percent) and a net drag reduction of 7 percent. The device drag for this shape was determined to be near laminar skin friction. The NACA 4409 airfoils suffered large regions of separated flow and produced no net drag reduction.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 85-0520
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  • 9
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    A search for the effect of a high frequency spark on boundary-layer transition at Mach 8.5 (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An experimental investigation of the use of a high frequency spark to promote early boundary layer transition on a wind tunnel model was conducted at a Mach number of 8.5. Test variables included four electrode configurations, a frequency range from 10 kHz to 50 kHz, and various power inputs to the spark. The general conclusion obtained from this investigation is that over the parameter range, the high frequency spark is ineffective in inducing early transition at the test Mach number.
    Keywords: FLUID MECHANICS
    Type: NASA-TM-X-2610 , L-8314
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  • 10
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    Fluid flow analysis of a hot-core hypersonic wind-tunnel nozzle concept (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A hypersonic-wind-tunnel nozzle concept which incorporates a hot-core flow surrounded by an annular flow of cold air offers a promising technique for maximizing the model size while minimizing the power required to heat the test core. This capability becomes especially important when providing the true-temperature duplication needed for hypersonic propulsion testing. Several two-dimensional wind-tunnel nozzle configurations that are designed according to this concept are analyzed by using recently developed analytical techniques for prediction of the boundary-layer growth and the mixing between the hot and cold coaxial supersonic airflows. The analyses indicate that introduction of the cold annular flow near the throat results in an unacceptable test core for the nozzle size and stagnation conditions considered because of both mixing and condensation effects. Use of a half-nozzle with a ramp on the flat portion does not appear promising because of the thick boundary layer associated with the extra length. However, the analyses indicate that if the cold annular flow is introduced at the exit of a full two-dimensional nozzle, an acceptable test core will be produced. Predictions of the mixing between the hot and cold supersonic streams for this configuration show that mixing effects from the cold flow do not appreciably penetrate into the hot core for the large downstream distances of interest.
    Keywords: FACILITIES, RESEARCH, AND SUPPORT
    Type: NASA-TN-D-6768 , L-8179
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