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  • Other Sources  (930)
  • AERODYNAMICS  (626)
  • INSTRUMENTATION AND PHOTOGRAPHY  (304)
  • 1990-1994  (930)
  • 1985-1989
  • 1990  (930)
  • 1
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    Instantaneous velocity field measurement of objects in coaxial rotation using digital image velocimetry (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The instantaneous velocity fields of time-dependent flows, or of a collection of objects moving with spatially varying velocities, can be measured by means of digital image velocimetry (DIV). DIV overcomes several shortcomings of such existing techniques as laser-speckle or particle-image velocimetry. Attention is presently given to numerically generated images representing objects in uniform motion which are then used for the experimental validation of DIV.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: ; : Mechanical behavio
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    NASA TECHNICAL REPORTS
  • 2
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    Design criteria for small coded aperture masks in gamma-ray astronomy (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Most theoretical work on coded aperture masks in X-ray and low-energy gamma-ray astronomy has concentrated on masks with large numbers of elements. For gamma-ray spectrometers in the MeV range, the detector plane usually has only a few discrete elements, so that masks with small numbers of elements are called for. For this case it is feasible to analyze by computer all the possible mask patterns of given dimension to find the ones that best satisfy the desired performance criteria. A particular set of performance criteria for comparing the flux sensitivities, source positioning accuracies and transparencies of different mask patterns is developed. The results of such a computer analysis for masks up to dimension 5 x 5 unit cell are presented and it is concluded that there is a great deal of flexibility in the choice of mask pattern for each dimension.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Nuclear Instruments and Methods in Physics Research, Section A - Accelerators, Spectrometers, Detectors, and Associated Equipment (ISSN 0168-9002); A295; 477-488
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    NASA TECHNICAL REPORTS
  • 3
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    Isotopically enriched germanium detectors for astrophysical gamma-ray spectroscopy (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A study is presented of the instrumental background in astrophysical gamma-ray spectrometers using isotopically enriched germanium detectors. Calculations show that the beta-decay background, which is the largest component between approximately 0.1 and 1.0 MeV in balloonborne and satellite spectrometers, is dominated by the activation of Ge-74. This component can be reduced by an order of magnitude using detectors enriched to more than 80 percent in (Ge-70). The predicted reduction in the total background for current balloonborne instruments is more than a factor of 1.7 between 0.2 and 1.0 MeV. For future satellite instruments, the reduction in this energy range is by more than a factor of 5.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Nuclear Instruments and Methods in Physics Research, Section A - Accelerators, Spectrometers, Detectors, and Associated Equipment (ISSN 0168-9002); 292; 505-516
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  • 4
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    A comparison of optimization-based approaches for solving the aerodynamic design problem (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: Three optimization-based methods for solving aerodynamic design problems are compared. The Euler equations for one-dimensional duct flow was used as a model problem, and the three methods are compared for efficiency, robustness, and implementation difficulty. The smoothness of the design problem with respect to different shock-capturing finite difference schemes, and in the presence of grid refinement, is investigated.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 77-88
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  • 5
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    ENSAERO - A multidisciplinary program for fluid/structural interaction studies of aerospace vehicles (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A computational procedure is developed that uses a moving zonal grid concept to model complex flexible aerospace vehicles. The Euler/Navier-Stokes equations are used to model the flow, and computations are made using efficient methods based on both central and upwind schemes. The structure is represented by a finite element method which can model general aerospace vehicles. Provisions are made to accommodate other disciplines such as controls and thermal loads. The code is capable of computing unsteady flows on flexible wings with vortical flows. Adaptation of this procedure for parallel processing and validation for complete aerospace configurations is in progress.
    Keywords: AERODYNAMICS
    Type: Computing Systems in Engineering (ISSN 0956-0521); 1; 2-4,
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  • 6
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    Aerothermodynamics of sprint-type manned Mars missions (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 27; 589-596
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  • 7
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    Experimental investigation of oscillating cascade aerodynamics (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A series of experiments are performed in the NASA Lewis Transonic Oscillating Cascade Facility to provide fundamental data quantifying the high subsonic and transonic steady and oscillating aerodynamics of a biconvex airfoil cascade at realistic reduced frequency values for all interblade phase angles. This is accomplished by developing and utilizing an unsteady aerodynamic influence-coefficient technique in which only one cascaded airfoil is oscillated at a time. The vector summation of the resulting airfoil-surface unsteady pressures (measured on a dynamically instrumented airfoil) makes it possible to determine the unsteady aerodynamics of an equivalent cascade with all airfoils oscillating at any specified interblade phase angle.
    Keywords: AERODYNAMICS
    Type: Journal of Aerospace Power (ISSN 1000-8055); 5; 275-282
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  • 8
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    Method for measuring temperatures and densities in hypersonic wind tunnel air flows using laser-induced O2 fluorescence (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Laser-induced fluorescence in oxygen, in combination with Raman scattering, is shown to be an accurate means by which temperature, density, and their fluctuations owing to turbulence can be measured in air flows associated with high-speed wind tunnels. For temperatures above 60 K and densities above 0.01 amagat, the uncertainties in the temperature and density measurements can be less than 2 percent, if the signal uncertainties are dominated by photon statistical noise. The measurements are unaffected by collisional quenching and can be achieved with laser fluences for which nonlinear effects are insignificant. Temperature measurements using laser-induced fluorescence alone have been demonstrated at known densities in the range of low temperatures and densities which are expected in a hypersonic wind tunnel.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics (ISSN 0003-6935); 29; 4873-488
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  • 9
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    Ideal efficiency of propellers - Theodorsen revisited (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Theodorsen's 1948 analog evaluation of the parameters governing the ideal (friction-free) efficiency of propellers is updated and extended by computer. The results are presented both in his format and in a much more convenient one by Kramer that avoids iteration: curves of power coefficient at constant ideal efficiency are plotted vs propeller advance coefficient. The curves for a wide range of blade numbers are collapsed into just three sets (with some approximation) by use of multiple, shifted (and distorted) abscissae scales. Along with an overview of Theodorsen's theory, analytic asymptotic results at low and high advance coefficients are given. At the low end, the disagreement with actuator disk theory is given support and physical interpretation. At the high end, exact agreement is found with the thrust of a slender twisted delta propeller.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 27; 810-819
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  • 10
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    Supersonic far-field boundary conditions for transonic small-disturbance theory (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 27; 764-770
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