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  • 1990-1994  (14)
  • 1
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    Drag Reduction in Nature (1991)
    Annual Reviews
    Details
    Publication Date: 1991-01-01
    Print ISSN: 0066-4189
    Electronic ISSN: 1545-4479
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Annual Reviews
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    PAPER CURRENT
  • 2
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    Longitudinal vortex control - Techniques and applications (The 32nd Lanchester Lecture) (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A summary is presented of vortex control applications and current techniques for the control of longitudinal vortices produced by bodies, leading edges, tips and intersections. Vortex control has up till now been performed by many approaches in an empirical fashion, assisted by the essentially inviscid nature of much of longitudinal vortex behavior. Attention is given to Reynolds number sensitivities, vortex breakdown and interactions, vortex control on highly swept wings, and vortex control in juncture flows.
    Keywords: AERODYNAMICS
    Type: Aeronautical Journal (ISSN 0001-9240); 96; 958; p. 293-312.
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Supersonic laminar flow control (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A development status evaluation is presented for the theoretical understanding and design conceptualization of boundary layer control (BLC) systems applicable to supersonic transports, such as the currently envisioned NASA High Speed Civil Transport. By reducing fuel burned, supersonic BLC techniques could expand ranges to Pacific-crossing scales, while lowering sonic boom effects and upper-atmosphere pollution and even reducing skin friction temperature. The critical consideration for supersonic BLC is the presence of wave effects.
    Keywords: AERODYNAMICS
    Type: In: Natural laminar flow and laminar flow control (A93-41776 17-02); p. 233-245.
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    High-Reynolds-number test requirements in low-speed aerodynamics (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Research requirements to an ultra-high-Reynolds-number liquid helium facility are reviewed. Aerodynamic research areas under consideration include wave vortex hazard reduction, vortex control and diagnostics for maneuvering fighter aircraft, and performance of high-lift devices.
    Keywords: AERODYNAMICS
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Drag reduction in nature (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Recent studies on the drag-reducing shapes, structures, and behaviors of swimming and flying animals are reviewed, with an emphasis on potential analogs in vehicle design. Consideration is given to form drag reduction (turbulent flow, vortex generation, mass transfer, and adaptations for body-intersection regions), skin-friction drag reduction (polymers, surfactants, and bubbles as surface 'additives'), reduction of the drag due to lift, drag-reduction studies on porpoises, and drag-reducing animal behavior (e.g., leaping out of the water by porpoises). The need for further research is stressed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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    NASA TECHNICAL REPORTS
  • 6
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    Comment on: The current status of turbulence modeling in CFD and its future prospects (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Information is given in viewgraph form on computational fluid dynamics (CFD). Topics covered include the fundamental problem with conventional turbulence modeling, the fundamental problems with the state-of-the-art turbulence modeling approach of 'eddy viscosity', major problems with Reynolds stress equation (RSE) closures, RSE challenges that are probably addressable within the context of Reynolds averaging, RSE challenges which may require theoretical/numerical spectral adjuncts for satisfactory solutions, tools available to aid RSE modeling, and a simplex view of the status of turbulence modeling.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, Workshop on Engineering Turbulence Modeling; p 17-37
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Aircraft Drag Reduction (1992)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: This paper reviews aerodynamic drag reduction for friction, wave and vortex drag associated with supersonic cruise aircraft and suggests approaches and research directions which cover the spectrum from possibly significant to revolutionary. Various synergisms are also included, especially in regard to suction laminar flow control and flow separation control at cruise. The former may also enable improved low speed, high lift systems, lift to drag ratio for subsonic cruise, reduced parasitic viscous drag for favorable interference wave drag reduction approaches, and turbulent skin friction reduction via slot injection. Flow separation control at cruise proffers opportunities for increased leading edge thrust, increased lift increment from upper surface, increased fuselage lift/camber for wave drag due to lift reduction, improved performance of various favorable interference wave drag reduction schemes, as well as possibly better low speed, high-schemes and wing cruise performance. More speculative approaches include multi-stage aircraft, thrust vectoring for lift augmentation, as well as trim, and a number of conceptual wave and vortex drag reduction schemes.
    Keywords: AERODYNAMICS
    Type: AGARD, Special Course on Skin Friction Drag Reduction; 16 p
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Turbulence modeling in aerodynamic shear flows - Status and problems (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This paper briefly summarizes the status and problems of turbulence modeling for aerodynamical applications. For complex flows the 'approach of choice' is (increasingly) full second-order (Reynolds stress equation) closure. These closures have not yet developed to anywhere near their full potential, significant further research is required especially regarding length-scale equations, representation of pressure-strain correlations, and wall region treatments. Recent developments in computer capability, algorithms, numerical simulations, theory and quantitative flow visualization should assist in and hasten this research. Several problem areas such as shock interaction and discrete dynamic instabilities of turbulent flows may require mega-to-large eddy simulation or theoretical adjuncts.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-0214
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Boundary layer transition in hypersonic flows (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This paper summarizes some of the recent progress made at NASA Langley Research Center in the understanding, prediction and modeling of high speed boundary-layer transition. Linear and nonlinear theories together with large-eddy and direct numerical simulations have been used to understand various aspects of the transition problem while low disturbance 'quiet' tunnels provide means for validating the theoretical results.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 90-5232
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Investigation of several passive and active methods for turbulent flow separation control (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Relative performance of several passive and active methods for controlling two-dimensional turbulent separated flow associated with a curved backward-facing ramp were investigated at low speeds. Surface static pressure measurement and oil flow visualization results indicate that submerged vortex generators, vortex generator jets, elongated arches at +-alpha, and large-eddy breakup devices at +-alpha placed near the baseline separation location reduce flow separation and increase pressure recovery. Spanwise cylinders reduce flow separation but decrease pressure recovery downstream. Arches with alpha = 0 deg, Helmholtz resonators, and Viets' fluidic flappers examined so far have no significant effect in reducing separation. Wall cooling computation indicates that separation delay on a partially cooled ramp is nearly the same as on a fully-cooled ramp while minimizing the frictional drag increase associated with the wall cooling process.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 90-1598
    Format: text
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    NASA TECHNICAL REPORTS
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