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  • Other Sources  (684)
  • AERODYNAMICS  (684)
  • Life and Medical Sciences
  • 1990-1994  (684)
  • 1910-1914
  • 1991  (684)
  • 1
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    Scientific Balloons (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: This video discusses how NASA uses large helium-filled balloons to take payloads up 25 miles to the edge of space to gather data. Balloons provide a cost effective approach to reach these heights.
    Keywords: AERODYNAMICS
    Type: NASA-TM-109907 , NONP-NASA-VT-94-23149 , ASR-258
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Unstructured and adaptive mesh generation for high Reynolds number viscous flows (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A method for generating and adaptively refining a highly stretched unstructured mesh suitable for the computation of high-Reynolds-number viscous flows about arbitrary two-dimensional geometries was developed. The method is based on the Delaunay triangulation of a predetermined set of points and employs a local mapping in order to achieve the high stretching rates required in the boundary-layer and wake regions. The initial mesh-point distribution is determined in a geometry-adaptive manner which clusters points in regions of high curvature and sharp corners. Adaptive mesh refinement is achieved by adding new points in regions of large flow gradients, and locally retriangulating; thus, obviating the need for global mesh regeneration. Initial and adapted meshes about complex multi-element airfoil geometries are shown and compressible flow solutions are computed on these meshes.
    Keywords: AERODYNAMICS
    Type: International Conference on Numerical Grid Generation in Computational Fluid Dynamics and Related Fields; Jun 03, 1991 - Jun 07, 1991; Barcelona; Spain
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    NASA TECHNICAL REPORTS
  • 3
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    Waves and thermodynamics in high Mach number propulsive ducts (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The propulsive effects of waves in ducts, especially at high Mach numbers, are investigated, focusing on drag and thrust and on the conversion of heat into waves which produce thrust. It is shown that essentially all of the work done by an expanding fluid passing through a duct at high Mach number is delivered in the form of waves, and that duct surface angles exist that are optimum for the production of thrust from a wave. The effects of wave phenomena on drag and thrust are considered by extending the concept of a Busemann biplane into that of a 'Busemann scramjet, taking 'off-design' performance into account. An idealized model of a streamtube with heat addition is developed, and flow mechanisms involved in generating thrust by the expansion of this streamtube in an exhaust nozzle are examined.
    Keywords: AERODYNAMICS
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    NASA TECHNICAL REPORTS
  • 4
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    Passive control of supersonic cavity flowfields (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A computational investigation has been conducted to study the effect and mechanisms of the passive control of a supersonic flow over a rectangular two-dimensional cavity. The passive control was included through the use of a porous surface over a vent chamber in the floor of the cavity. The passive control effectively suppressed the low-frequency pressure oscillations for the open type cavity, (length-to-depth ratio = 6.0). The mechanism for the suppression was observed to be the stabilization of the motion of the free shear layer. For the closed type cavity flow, (length-to-depth ratio = 17.5), the passive control modified the flowfield to nearly that of an open type cavity flow; further the cavity drag was reduced by a factor of four. The computational results of both cases showed good agreement with the available experimental data and the predictions of a semiempirical formula. This study demonstrates that the passive control concept can be used to improve the aerodynamic characteristics of open and closed cavity flowfields.
    Keywords: AERODYNAMICS
    Type: SAE PAPER 912153
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    NASA TECHNICAL REPORTS
  • 5
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    Computational aerodynamics - The next generation (1991)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: Continued advances in the various elements that comprise the field of computational fluid dynamics (CFD) are promoting a radically different approach to the aerodynamic design and analysis of aerospace vehicles and systems. The elements of CFD generally include numerical algorithm development, transition and turbulence modeling, surface modeling, and grid generation, scientific visualization and validation methodologies. This paper discusses the research progress and prospects for the future in each of these elements within NASA's CFD and Experimental Validation Program. The applicability of computational methods for the purposes of understanding complex flow phenomena, exploring aerodynamic concepts, and providing vehicle-design input is also addressed.
    Keywords: AERODYNAMICS
    Type: SAE PAPER 911988 , International Pacific Air and Space Technology Conference; Oct 07, 1991 - Oct 11, 1991; Gifu; Japan
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  • 6
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    Design and off-design performance analysis of a maximum compression/minimum drag hypersonic forebody (1991)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: The performance of a funnel-shaped hypersonic vehicle forebody is shown at its design Mach number of 15 and at two lower off-design Mach numbers. Inlet flow quality is presented by contour plots of flow angularity and pressure. Performance is indicated by mass capture ratio, total pressure recovery, kinetic energy efficiency and drag.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-3179
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    NASA TECHNICAL REPORTS
  • 7
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    Swept wing attachment line contamination fence (1991)
    In:  CASI
    Details
    Publication Date: 2019-08-14
    Description: A device for controlling attachment line contamination on an airfoil is presented. A fence is installed on the leading edge of the airfoil in the freestream direction perpendicular to the airfoil, outboard of the fuselage boundary layer. The inboard side of the fence arrests the spanwise movement of the turbulent boundary layer while the laminar boundary layer on the outboard side of the fence eliminates any further turbulent contamination of the attachment line.
    Keywords: AERODYNAMICS
    Type: NAS 1.71:LAR-13400-1
    Format: application/pdf
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  • 8
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    The computation of three-dimensional flows using unstructured grids (1991)
    In:  Other Sources
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    Publication Date: 2019-08-14
    Description: A general method is described for automatically discretizing, into unstructured assemblies of tetrahedra, the three-dimensional solution domains of complex shape which are of interest in practical computational aerodynamics. An algorithm for the solution of the compressible Euler equations which can be implemented on such general unstructured tetrahedral grids is described. This is an explicit cell-vertex scheme which follows a general Taylor-Galerkin philosophy. The approach is employed to compute a transonic inviscid flow over a standard wing and the results are shown to compare favorably with experimental observations. As a more practical demonstration, the method is then applied to the analysis of inviscid flow over a complete modern fighter configuration. The effect of using mesh adaptivity is illustrated when the method is applied to the solution of high speed flow in an engine inlet.
    Keywords: AERODYNAMICS
    Type: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 87; 3-Feb
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    NASA TECHNICAL REPORTS
  • 9
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    A Numerical Study of Hypersonic Forebody/Inlet Integration Problem (1991)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: A numerical study of hypersonic forebody/inlet integration problem is presented in the form of the view-graphs. The following topics are covered: physical/chemical modeling; solution procedure; flow conditions; mass flow rate at inlet face; heating and skin friction loads; 3-D forebogy/inlet integration model; and sensitivity studies.
    Keywords: AERODYNAMICS
    Type: Computational Fluid Dynamics Code Validation(Calibration. JANNAF Airbreathing Propulsion Subcommittee Workshop: High-Speed Inlet Forebody Interactions; 131-154|JANNAF Workshop on CFD Code Validation/Calibration for High-Speed Inlet Forebody Interactions; Jan 10, 1991 - Jan 11, 1991; Reno, NV; United States
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  • 10
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    Simulation and modeling of homogeneous compressible turbulence under isotropic mean compression (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: Compressible homogeneous turbulence subjected to isotropic mean compression is simulated numerically for high and low turbulent Mach numbers, at various compression rates. It is found that at low Mach numbers, the effects of viscosity variations on the development of the turbulent kinetic energy can be significant. A model consistent with the invariance of the Navier-Stokes equations to spherical compression, that takes into account variable viscosity effects is proposed. At high Mach numbers, the distribution of energy between the acoustic and solenoid fields is found to depend upon initial conditions. The simulation results are also used to evaluate two-equation compressible turbulence models.
    Keywords: AERODYNAMICS
    Type: Symposium on Turbulent Shear Flows; Sept. 9-11, 1991; Munich; Germany
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