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  • 1
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    Conservative full-potential model for unsteady transonic rotor flows (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: AIAA Journal (ISSN 0001-1452); 25; 193-198
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  • 2
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    Numerical modeling of the vortex/airfoil interaction (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A modeling of the vortex-airfoil interaction is presented in which the finite-area of the real vortices is taken into consideration. Two vortex models are used. In the first, a disturbed piece of vorticity layer is simulated by four rows of discrete vortices of small strength. In the second, a number of discrete vortices is arranged within a circle. The first model may simulate a shear layer or a wake, while the second, a well-formed vortex. The method was applied to the calculation of the pressure induced on the surface of the airfoil by the interacting vortex. Both models give similar results. It was found that for large distances of the vortex from the surface of the airfoil, the consideration or not of the finite-area of the vortex is not a significant factor in determining the induced pressure field. However, when the distance of the vortex from the surface is reduced, its shape is distorted and the induced pressure pulses have lower amplitude than the ones induced by an equivalent point vortex. In the limit, where the vortex impinges on the leading edge of the airfoil, it is split into two and the time dependent pressure coefficient takes even negative values at some time intervals.
    Schlagwort(e): AERODYNAMICS
    Materialart: AIAA Journal (ISSN 0001-1452); 25; 5-11
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  • 3
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    Numerical investigation of unsteady inlet flowfields (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: AIAA Journal (ISSN 0001-1452); 25; 75-81
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  • 4
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    Hypersonic merged-layer flow on a sphere (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 1; 21-27
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  • 5
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    Theoretical analysis of aircraft afterbody flow (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Computational methods solving the thin shear layer formulation of the compressible, Reynolds-averaged Navier-Stokes equations are presently used to investigate the strongly interactive flow field about aircraft afterbodies. Solutions for a variety of axisymmetric afterbody and nozzle geometries are solved by means of a time-dependent implicit numerical algorithm for both subsonic and supersonic external flows, and the results obtained are compared with experimental data. A novel adaptive-grid technique is used to resolve flow regimes having large gradients, as well as to improve the accuracy and efficiency of the computational scheme.
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 496-503
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  • 6
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    Efficient self-consistent viscous-inviscid solutions for unsteady transonic flow (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 737-744
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  • 7
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    Application of axisymmetric analog for calculating heating in three-dimensional flows (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 296-302
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  • 8
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    Prospects for destructive self-induced interactions in a vortex pair (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 433-440
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  • 9
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    Speckle noise reduction of 1-look SAR imagery (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Speckle noise is inherent to synthetic aperture radar (SAR) imagery. Since the degradation of the image due to this noise results in uncertainties in the interpretation of the scene and in a loss of apparent resolution, it is desirable to filter the image to reduce this noise. In this paper, an adaptive algorithm based on the calculation of the local statistics around a pixel is applied to 1-look SAR imagery. The filter adapts to the nonstationarity of the image statistics since the size of the blocks is very small compared to that of the image. The performance of the filter is measured in terms of the equivalent number of looks (ENL) of the filtered image and the resulting resolution degradation. The results are compared to those obtained from different techniques applied to similar data. The local adaptive filter (LAF) significantly increases the ENL of the final image. The associated loss of resolution is also lower than that for other commonly used speckle reduction techniques.
    Schlagwort(e): COMMUNICATIONS AND RADAR
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  • 10
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    Influence of forebody cross-sectional shape on wing vortex-burst location (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 645-652
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  • 11
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    Aerothermodynamics of transatmospheric vehicles (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 594-602
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  • 12
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    On the optimum polarizations of incoherently reflected waves (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The Stokes scattering operator is noted to be the most useful characterization of incoherent scattering in radar imaging; the polarization that would yield an optimum amount of power received from the scatterer is obtained by assuming a knowledge of the Stokes scattering operator instead of the 2x2 scattering matrix with complex elements. It is thereby possible to find the optimum polarizations for the case in which the scatterers can only be fully characterized by their Stokes scattering operator, and the case in which the scatterer can be fully characterized by the complex 2x2 scattering matrix. It is shown that the optimum polarizations reported in the literature form the solution for a subset of a more general class of problems, so that six optimum polarizations can exist for incoherent scattering.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-35; 818-825
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  • 13
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    Low-loss offset feeds for electrically large symmetric dual-reflector antennas (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Circularly symmetric, dual reflector, high gain antenna systems often require feeds placed off the system's axis because of the need for multiple feeds to use the reflector antenna. Also, the constraint requiring the hyperboloid or shaped subreflector to remain circularly symmetric is sometimes added. In a Cassegrainian system, the subreflector and feed may be rotated off axis around the paraboloid focus and retain main reflector focusing. However, substantial spillover results in considerable noise with a high gain/low noise temperature system. In a shaped system, the tilt of the shaped subreflector and feed together results in substantial defocusing as well as spillover noise. If the subreflector is tilted approximately one-half the angle of the feed tilt in either the Casegrainian or the dual shaped reflector antenna, it is found that spillover and noise are substantially reduced with tolerable defocusing. An extensive numerical analysis of these effects was conducted to determine the characteristics of a planned 70-meter, dual shaped reflector versus Cassegrainian antenna and to gain some understanding of the cause of the observed effects.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-35; 745-755
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  • 14
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    Vortical flow management techniques (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The aerodynamic performance and controllability of advanced, highly maneuverable supersonic aircraft can be enhanced by means of 'vortex management', which refers to the purposeful manipulation and reordering of stable and concentrated vortical structures due to flow separations from highly swept leading edges and slender forebodies at moderate-to-high angles-of-attack. Attention is presently given to a variety of results obtained in the course of experiments on generic research models at NASA Langley, clarifying their underlying aerodynamics and evaluating their performance-improvement potential. The vortex-management concepts discussed encompass aerodynamic compartmentation of highly swept leading edges, vortex lift augmentation and modulation, and forebody vortex manipulation.
    Schlagwort(e): AERODYNAMICS
    Materialart: Progress in Aerospace Sciences (ISSN 0376-0421); 24; 3, 19; 173-224
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  • 15
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    Analysis of a dual-wavelength surface reference radar technique (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The use of the single-wavelength surface reference technique (SRT), the standard dual-wavelength technique (DWT), and dual-wavelength surface reference technique (DSRT) for measuring precipitation from space is analyzed, and the results are compared. The characteristics of the three methods are described, and the surface return powers during clear air conditions are measured. It is observed that the rain rate estimates obtained with the DWT and DSRT are identical in form, and the surface reflectance can be derived from the estimates by replacing the rain reflectivity statistics with those of the backscattering cross section of the surface. The data reveal that the DSRT is more applicable than the SRT when the wavelength correlation in the backscattering cross section of the surface is high or when the mean values of the backscattering cross section at the two wavelengths are nearly equal.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); GE-25; 456-471
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  • 16
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    Lower-upper implicit scheme for high-speed inlet analysis (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: (Previously cited in issue 20, p. 2915, Accession no. A86-42687)
    Schlagwort(e): AERODYNAMICS
    Materialart: AIAA Journal (ISSN 0001-1452); 25; 1052
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  • 17
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    Transmitter pointing loss calculation for free-space optical communications link analyses (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: In calculating the performance of free-space optical communications links, the transmitter pointing loss is one of the two most important factors. It is shown in this paper that the traditional formula for the instantaneous pointing loss (i.e., for the transmitter telescope far-field beam pattern) is quite inaccurate. A more accurate and practical approximation is developed in which the pointing loss is calculated using a Taylor series approximation. The four-term series is shown to be accurate to 0.1 dB for the theta angles not greater than 0.9 lambda/D (wavelength/telescope diameter).
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: Applied Optics (ISSN 0003-6935); 26; 2055-205
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  • 18
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    Estimating the arrival times of photon-limited laser pulses in the presence of shot and speckle noise (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Maximum-likelihood (ML) receivers are frequently used to optimize the timing performance of laser-ranging and laser-altimetry systems in the presence of shot and speckle noise. Monte Carlo method was used to examine ML-receiver performance with return signals in the 10-5000-photoelectron (pe) range. The simulations were performed for shot noise only and for shot and speckle noise. The results agree with previous theory for signal strengths greater than about 100 pe's but show that the theory can significantly underestimate timing errors for weaker received signals. Sharp high-bandwidth features in the detected signals are shown to improve timing performance only if their signal levels are greater than 4-5 pe's.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: Optical Society of America, Journal, A: Optics and Image Science (ISSN 0740-3232); 4; 1080-108
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  • 19
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    Nonuniform sampling techniques for antenna applications (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: A two-dimensional sampling technique, which can employ irregularly spaced samples (amplitude and phase) in order to generate the complete far-field patterns is presented. The technique implements a matrix inversion algorithm, which depends only on the nonuniform sampled data point locations and with no dependence on the actual field values at these points. A powerful simulation algorithm is presented to allow a real-life simulation of many reflector/feed configurations and to determine the usefulness of the nonuniform sampling technique for the copolar and cross-polar patterns. Additionally, an overlapped window concept and a generalized error simulation model are discussed to identify the stability of the technique for recovering the field data among the nonuniform sampled data. Numerical results are tailored for the pattern reconstruction of a 20-m offset reflector antenna operating at L-band. This reflector is planned to be used in a proposed measurement concept of large antenna aboard the Space Shuttle, whereby it would be almost impractical to accurately control the movement of the Shuttle with respect to the RF source in prescribed directions in order to generate uniform sampled points. Also, application of the nonuniform sampling technique to patterns obtained using near-field measured data is demonstrated. Finally, results of an actual far-field measurement are presented for the construction of patterns of a reflector antenna from a set of nonuniformly distributed measured amplitude and phase data.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-35; 268-279
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  • 20
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    Laboratory measurements and a theoretical analysis of the TCT fading channel radio system (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: This paper documents the laboratory and theoretical performance of a pilot-aided digital radio system. The technique considered transmits a midband pilot tone to improve the receiver data detection performance in a multipath fading channel and is referred to as the tone calibrated technique (TCT). The performance of a 860 MHz prototype system carrying 2.4 kbit/s data under Rician fading conditions is reported. Both experimental and analytical results show that the error floor experienced with nonpilot-aided transmission methods is effectively removed by the TCT scheme, resulting in significant performance gains at high signal-to-noise ratio values. The paper also examines the TCT system performance under typical operating conditions and presents a new analysis of the TCT theoretical error probability.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: IEEE Transactions on Communications (ISSN 0090-6778); COM-35; 172-180
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  • 21
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    Channel simulation to facilitate mobile-satellite communications research (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The mobile-satellite-service channel simulator, which is a facility for an end-to-end hardware simulation of mobile satellite communications links is discussed. Propagation effects, Doppler, interference, band limiting, satellite nonlinearity, and thermal noise have been incorporated into the simulator. The propagation environment in which the simulator needs to operate and the architecture of the simulator are described. The simulator is composed of: a mobile/fixed transmitter, interference transmitters, a propagation path simulator, a spacecraft, and a fixed/mobile receiver. Data from application experiments conducted with the channel simulator are presented; the noise converison technique to evaluate interference effects, the error floor phenomenon of digital multipath fading links, and the fade margin associated with a noncoherent receiver are examined. Diagrams of the simulator are provided.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: IEEE Transactions on Communications (ISSN 0090-6778); COM-35; 47-56
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  • 22
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    Calculation of external-internal flow fields for mixed-compression inlets (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Supersonic inlet flows with mixed external-internal compressions were computed using a combined implicit-explicit (Beam-Warming-Steger/MacCormack) method for solving the three-dimensional unsteady, compressible Navier-Stokes equations in conservation form. Numerical calculations were made of various flows related to such inlet operations as the shock-wave intersections, subsonic spillage around the cowl lip, and inlet started versus unstarted conditions. Some of the computed results were compared with wind tunnel data.
    Schlagwort(e): AERODYNAMICS
    Materialart: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 64; 21-37
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  • 23
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    Some effects of interference flowfields on supersonic configurations (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 880-885
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  • 24
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    Supersonic airfoil optimization (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 873-879
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  • 25
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    Algebraic grid generation about wing-fuselage bodies (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: An algebraic procedure for generating boundary-fitted grids about wing-fuselage configurations is presented. A wing-fuselage configuration consists of two aircraft components specified by cross sections and mathematically represented by Coons' patches. Several grid blocks are constructed to cover the entire region surrounding the configuration, and each grid block maps into a computational cube. Grid points are first determined on the six boundary surfaces of a block and then in the interior. Grid points on the surface of the configuration are derived from the intersection of planes with the Coons' patch definition. Approximate arc length distributions along the resulting grid curves concentrate and disperse grid points. The two-boundary technique and transfinite interpolation are used to determine grid points on the remaining boundary surfaces and block interiors.
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 868-872
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  • 26
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    Planform effects for low-fineness-ratio multibody configurations at supersonic speeds (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 856-860
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  • 27
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    Improved finite-difference schemes for transonic potential flow calculations (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: AIAA Journal (ISSN 0001-1452); 25; 1456-146
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  • 28
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    Vortex simulation of forced/unforced mixing layers (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: AIAA Journal (ISSN 0001-1452); 25; 1417
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  • 29
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    Jacobi-Bessel analysis of reflector antennas with elliptical apertures (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Although many reflector antennas possess circular projected apertures, there are recent satellite and ground antenna applications for which it is desirable to employ reflectors with elliptical apertures. Here a modification of the Jacobi-Bessel expansion is presented for the diffraction analysis of reflectors with elliptical apertures. A comparative study is also performed between this modified Jacobi-Bessel algorithm and the one which uses the Jacobi-Bessel expansion over a circumscribing circular region. Numerical results are presented for offset reflectors with elliptical and circular apertures and the improved convergence properties of the modified algorithm are highlighted.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-35; 1070-107
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  • 30
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    Computed and experimental surface pressure and heating on 70-deg sphere cones (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 385-393
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  • 31
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    Evaluating roughness models of radar backscatter (1987)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Three radar backscatter roughness models were assessed using soil moisture data collected by the Space Shuttle flight 41G SIR-B SAR in an intensively farmed area. The SIR-B data swath included a large number of bare, dry fields with a large variety of surface roughnesses. The small perturbation model gives the best results, particularly when fields with a definite periodic row structure were omitted. The standard deviation of surface heights appears to be a good measure of relative roughness conditions, but the correlation length is not a good descriptor of the surface, and does not seem to be related in any way to the measured backscatter.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); GE-25; 709-713
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  • 32
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    Transition on swept leading edges at Mach 3.5 (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 710-717
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  • 33
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    Aerodynamic effects of distributed spanwise blowing on a fighter configuration (1987)
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 673-679
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  • 34
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    Roundoff noise analysis for digital signal power processors using Welch's power spectrum estimation (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The noise due to finite-word-length effects is analyzed for digital-signal power processors using Welch's power-spectrum estimation technique to measure the power of Gaussian random signals over a frequency band of interest. The input of the digital signal processor contains a finite-length time interval in which the true Gaussian signal is contaminated by Gaussian noise. The roundoff noise-to-signal ratio in the measurement of the signal power is derived, and computer simulations which validate the analytical results are presented. These results can be used in tradeoff studies of hardware design, such as the number of bits required at each processing stage. The results presented in this paper are currently being used in the design of a digital Doppler processor (Chi et al., 1986) for a radar scatterometer.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: IEEE Transactions on Acoustics, Speech, and Signal Processing (ISSN 0096-3518); ASSP-35; 784-795
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  • 35
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    Bifurcations in unsteady aerodynamics (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Nonlinear algebraic functional expansions are used to create a form for the unsteady aerodynamic response that is consistent with solutions of the time dependent Navier-Stokes equations. An enumeration of means of invalidating Frechet differentiability of the aerodynamic response, one of which is aerodynamic bifurcation, is proposed as a way of classifying steady and unsteady aerodynamic phenomena that are important in flight dynamics applications. Accommodating bifurcation phenomena involving time dependent equilibrium states within a mathematical model of the aerodynamic response raises an issue of memory effects that becomes more important with each successive bifurcation.
    Schlagwort(e): AERODYNAMICS
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  • 36
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    Computer graphic visualization of Orbiter lower surface boundary-layer transition (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 109-114
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  • 37
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    Hypersonic aerodynamics for an entry research vehicle (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 97
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  • 38
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    Drag reduction on a bluff body at yaw angles to 30 degrees (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The base separation alleviation and drag reduction effectiveness of transverse rectangular grooves and longitudinal v-grooves in the afterbody shoulder region of a bluff body is investigated for body yaw angles of 0-30 deg. The grooves are found to be beneficial in reducing both freestream and axial drag coefficients at yaw angles of up to 25 deg.
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 179-181
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  • 39
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    High-speed aerodynamics of several blunt-cone configurations (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 127-132
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  • 40
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    Induced-drag characteristics of crescent-moon-shaped wings (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 115-119
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  • 41
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    Parameter estimation based on Doppler frequency shifts (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: An acoustic source generates an amplitude-modulated tone, with Doppler variations due to the relative motion between source and receiver. A method is presented for real-time estimation of tone rest frequency and minimal distance between source and receiver, using digital signal processing techniques. The algorithm presented here was implemented using a Texas Instruments TMS32010 processor.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: IEEE Transactions on Aerospace and Electronic Systems (ISSN 0018-9251); AES-23; 31-39
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  • 42
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    The effect of the dynamic wet troposphere on radio interferometric measurements (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A statistical model of water vapor fluctuations is used to describe the effect of the dynamic wet troposphere on radio interferometric measurements. It is assumed that the spatial structure of refractivity is approximated by Kolmogorov turbulence theory, and that the temporal fluctuations are caused by spatial patterns moved over a site by the wind, and these assumptions are examined for the VLBI delay and delay rate observables. The results suggest that the delay rate measurement error is usually dominated by water vapor fluctuations, and water vapor induced VLBI parameter errors and correlations are determined as a function of the delay observable errors. A method is proposed for including the water vapor fluctuations in the parameter estimation method to obtain improved parameter estimates and parameter covariances.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: Radio Science (ISSN 0048-6604); 22; 251-265
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  • 43
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    Measured unsteady transonic aerodynamic characteristics of an elastic supercritical wing (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 225-230
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  • 44
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    Issues in packet radio network design (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The physical aspects of a packet radio network design, the automated management of the network, and the interface of the network to the users are examined. The networks provide data communications to users located over a broad geographic region where direct radio or wire connection between the source and destination user is not practical; the network consists of a radio, antenna, and digital controller. The physical connectivity, bandwidth-time-space management, channel access, and data link control of the network are analyzed. Consideration is given to link determination and control, routing and packet forwarding, congestion and flow control, and supported users management. The operation and management of a packet radio network, in particular network deployment and maintenance, network access methods, and its effect on the radio spectrum, are discussed. The performance and cost of a packet radio network are evaluated.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: IEEE, Proceedings (ISSN 0018-9219); 75; 6-20
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  • 45
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    Unsteady aerodynamics of blade rows (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The requirements placed on an unsteady aerodynamic theory intended for turbomachinery aeroelastic applications are discussed along with a brief description of the various theoretical models that are available to address these requirements. The main emphasis is placed on the description of a linearized inviscid theory which fully accounts for the effects of a nonuniform mean or steady flow on unsteady aerodynamic response. Although this theory has been developed primarily for blade flutter prediction, more general equations are presented which account for unsteady excitations due to incident external aerodynamic disturbances as well as those due to blade motions. The resulting equations consist of a system of three field equations along with conditions imposed at blade, wake and shock surfaces and in the far field. These equations can be solved to determine the fluctuations in all fluid dynamic properties throughout the required solution domain. Example solutions are presented to demonstrate several effects associated with nonuniform steady flows on the linearized unsteady aerodynamic response to prescribed blade motions.
    Schlagwort(e): AERODYNAMICS
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  • 46
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    Shock-capturing technique for hypersonic, chemically relaxing flows (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 481-488
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  • 47
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    Characteristics of a two-layer electromagnetically coupled rectangular patch antenna (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Experimental results on the characteristics of a two-layer electromagnetically coupled rectangular patch antenna are presented. The variations of pattern shape, 3 dB beam width, and impedance bandwidth with spacing s between the two layers are studied for s between 0 and 0.37 lambda (0). A relatively high-gain region is found for s between 0.31 lambda (0) and 0.37 lambda (0).
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: Electronics Letters (ISSN 0013-5194); 23; 1070-107
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  • 48
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    On the theory of the synthesis of single and dual offset shaped reflector antennas (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Two reflectors shaped so as to transforn a geometrical optics (GO) feed power pattern into a uniform amplitude and phase aperture distribution are indicated schematically. Single- and dual-shaped geometrical optics problems are solved via exact solutions obtained by progressive integration. It is concluded that an infinite set of such solutions exists.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-35; 887-896
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  • 49
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    Addressing the hypersonic simulation problem (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 334-341
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  • 50
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    Aerodynamic characteristics of biplanes with winglets (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 518-522
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  • 51
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    Imaging radar polarization signatures - Theory and observation (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Radar polarimetry theory is reviewed, and comparison between theory and experimental results obtained with an imaging radar polarimeter employing two orthogonally polarized antennas is made. Knowledge of the scattering matrix permits calculation of the scattering cross section of a scatterer for any transmit and receive polarization combination, and a new way of displaying the resulting scattering cross section as a function of polarization is introduced. Examples of polarization signatures are presented for several theoretical models of surface scattering, and these signatures are compared with experimentally measured polarization signatures. The coefficient of variation, derived from the polarization signature, may provide information regarding the amount of variation in scattering properties for a given area.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: Radio Science (ISSN 0048-6604); 22; 529-543
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  • 52
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    An expert system for scheduling requests for communications Links between TDRSS and ERBS (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: An ERBS-TDRSS Contact Planning System (ERBS-TDRSS CPS) is described which uses a graphics interface and the NASA Transportable Interference Engine. The procedure involves transfer of the ERBS-TDRSS Ground Track Orbit Prediction data to the ERBS flight operations area, where the ERBS-TDRSS CPS automatically generates requests for TDRSS service. As requested events are rejected, alternative context sensitive strategies are employed to generate new requested events until a schedule is completed. A report generator builds schedule requests for separate ERBS-TDRSS contacts.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: NASA, Goddard Space Flight Center, Proceedings of 1987 Goddard Conference on Space Applications of Artificial Intelligence (AI) and Robotics; 16 p
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  • 53
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    The Newcastle meteor radar (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: A brief history and development of the Newcastle Meteor Radar system is given. Also described are its geographical coordinates and its method of operation. The initial objective when the project was commenced was to develop an entirely digital analyzer capable of recognizing meteor echo signals and recording as many of their parameters as possible. This objective was achieved.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: International Council of Scientific Unions, Middle Atmosphere Program. Handbook for MAP, Volume 25; p 381-388
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  • 54
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    DSN 63 64-meter antenna S- and X-band efficiency and system noise temperature calibrations, July 1986 (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: The Deep Space Network (DSN) 64-meter antenna in Spain (DSN 63) has been calibrated prior to its upgrading to a 70-meter high efficiency configuration in preparation for the Voyager Neptune encounter in August 1989. The S-band (2285 MHz) and X-band (8420 MHz) effective area efficiency and system noise temperature calibrations were carried out during July 1986 to establish a baseline system performance for this station. It is expected that the 70-meter will result in at least a 1.9 dB G/T improvement at X-band relative to the 64-meter baseline reference.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: The Telecommunications and Data Acquisition Report; p 103-115
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  • 55
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    Soft-decision decoding of some block codes (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: The performance of certain binary block codes with soft-decision decoding is evaluated by simulation. A construction is proposed to introduce memory on block codes, and simulation results are shown for a trellis code derived from the Nordstrom-Robinson code.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: The Telecommunications and Data Acquisition Report; p 76-80
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  • 56
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    Systolic arrays and stack decoding (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: The application of systolic priority queues to the sequential stack decoding algorithm is discussed in a review of the work of K. Yao and C. Y. Chang. Using a systolic array architecture, one can significantly improve the performance of such algorithms at high signal-to-noise ratios.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: The Telecommunications and Data Acquisition Report; p 50-53
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  • 57
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    Reduction of ground noise in the transmitter crowbar instrumentation system by the use of baluns and other noise rejection methods (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Electrical noise interference in the transmitter crowbar monitoring instrumentation system creates false sensing of crowbar faults during a crowbar firing. One predominant source of noise interference is the conduction of currents in the instrumentation cable shields. Since these circulating ground noise currents produce noise that is similar to the crowbar fault sensing signals, such noise interference reduces the ability to determine true crowbar faults.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: The Telecommunications and Data Acquisition Report; p 27-31
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  • 58
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    CFD applications: The Lockheed perspective (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: The Numerical Aerodynamic Simulator (NAS) epitomizes the coming of age of supercomputing and opens exciting horizons in the world of numerical simulation. An overview of supercomputing at Lockheed Corporation in the area of Computational Fluid Dynamics (CFD) is presented. This overview will focus on developments and applications of CFD as an aircraft design tool and will attempt to present an assessment, withing this context, of the state-of-the-art in CFD methodology.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA. Ames Research Center, Supercomputing in Aerospace; p 77-85
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  • 59
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    Digital Autonomous Terminal Access Communication (DATAC) system (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: In order to accommodate the increasing number of computerized subsystems aboard today's more fuel efficient aircraft, the Boeing Co. has developed the DATAC (Digital Autonomous Terminal Access Control) bus to minimize the need for point-to-point wiring to interconnect these various systems, thereby reducing total aircraft weight and maintaining an economical flight configuration. The DATAC bus is essentially a local area network providing interconnections for any of the flight management and control systems aboard the aircraft. The task of developing a Bus Monitor Unit was broken down into four subtasks: (1) providing a hardware interface between the DATAC bus and the Z8000-based microcomputer system to be used as the bus monitor; (2) establishing a communication link between the Z8000 system and a CP/M-based computer system; (3) generation of data reduction and display software to output data to the console device; and (4) development of a DATAC Terminal Simulator to facilitate testing of the hardware and software which transfer data between the DATAC's bus and the operator's console in a near real time environment. These tasks are briefly discussed.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: NASA. Langley Research Center Joint University Program for Air Transportation Research, 1984; p 49-56
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    Direct simulation of hypersonic flows over blunt wedges (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 1; 97-104
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  • 61
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    Supersonic boundary-layer transition on the LaRC F-106 and the DFRF F-15 aircraft. Part 2: Aerodynamic predictions (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: In the leading edge region, the measured pressure distributions exhibit extreme variations from strong suction peaks to a pressure maximum at the attachment line. These variations occur over short distances on the wing surface, and their character changes with changes in Mach number and angle of attack. The data/theory comparisons show that the character of the measured pressure distributions is well predicted for every Mach number and/or angle of attack condition considered. There is good agreement between theory and experiment for the location of the attachment line and suction peaks. The pressure magnitudes are well represented in the critical leading edge region, including the pressure maximum on the attachment line. The wing/body/inlet results agree well with the wing alone back to about 20 percent of chord where the upper surface suction peak typically occurs. The largest differences between theory and measurement always occur in the vicinity of suction peaks, with the difference being approximately 15 percent or less. In regions of largest error, the predicted pressures underestimate the suction peak strength for each case considered. The ability of the NCOREL code to reproduce wing pressure characteristics is shown.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 3; p 1015-1024
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  • 62
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    Supersonic boundary-layer transition on the LaRC F-106 and the DFRF F-15 aircraft. Part 1: Transition measurements and stability analysis (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: For the case of the F-15 flight tests, boundary layer transition was observed up to Mach numbers of 1.2. For very limited and specific flight conditions, laminar flow existed back to about 20 percent chord on the surface clean up glove. Hot film instrumentation was effective for locating the region of transition. For the F-106 flight tests, transition on the wing or vertical tail generally occurred very near the attachment line. Transition was believed to be caused by either attachment line contamination or strong cross flow development due to the high sweep angles of the test articles. The compressibility analysis showed that cross flow N-factors were in the range of 5 to 12 at transition.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 3; p 997-1014
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    Experimental and theoretical investigation of boundary-layer instability mechanisms on a swept leading edge at Mach 3.5 (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: A brief outline of the experimental and theoretical investigation of boundary layer instability mechanisms on a swept leading edge at Mach 3.5 is presented. Transition is affected by wind tunnel noise only when roughness is present. Local bar-R sub * Reynolds number and k/eta sub * are useful correlation parameters for a wide range of free stream Mach numbers. Stability theory is in good agreement with the experimental cross flow vortex wavelength. These conclusions are briefly discussed.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 3; p 981-995
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    The effects of wall surface defects on boundary-layer transition in quiet and noisy supersonic flow (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: The design of supersonic vehicles with laminar flow control and vehicles such as the Space Shuttle requires information on allowable transition tolerances to fabrication defects such as discrete surface roughness and waviness. A relatively large data base on the effects of discrete roughness on transition exists for subsonic and supersonic speeds. The existing supersonic wind tunnel transition data are contaminated by wind tunnel noise emanating from the turbulent boundary layers on the nozzle walls. Roughness and waviness transition data obtained in a quiet Mach 3.5 supersonic wind tunnel are compared with those obtained in conventional noisy flows.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 3; p 965-980
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  • 65
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    Supersonic laminar-flow control (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Detailed, up to date systems studies of the application of laminar flow control (LFC) to various supersonic missions and/or vehicles, both civilian and military, are not yet available. However, various first order looks at the benefits are summarized. The bottom line is that laminar flow control may allow development of a viable second generation SST. This follows from a combination of reduced fuel, structure, and insulation weight permitting operation at higher altitudes, thereby lowering sonic boom along with improving performance. The long stage lengths associated with the emerging economic importance of the Pacific Basin are creating a serious and renewed requirement for such a vehicle. Supersonic LFC techniques are discussed.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 3; p 923-946
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    Experimental and numerical analyses of laminar boundary-layer flow stability over an aircraft fuselage forebody (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Fuelled by a need to reduce viscous drag of airframes, significant advances have been made in the last decade to design lifting surface geometries with considerable amounts of laminar flow. In contrast to the present understanding of practical limits for natural laminar flow over lifting surfaces, limited experimental results are available examining applicability of natural laminar flow over axisymmetric and nonaxisymmetric fuselage shapes at relevantly high length Reynolds numbers. The drag benefits attainable by realizing laminar flow over nonlifting aircraft components such as fuselages and nacelles are shown. A flight experiment to investigate transition location and transition mode over the forward fuselage of a light twin engine propeller driven airplane is examined.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 3; p 861-886
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    Wind tunnel results of the high-speed NLF(1)-0213 airfoil (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Wind tunnel tests were conducted to evaluate a natural laminar flow airfoil designed for the high speed jet aircraft in general aviation. The airfoil, designated as the High Speed Natural Laminar Flow (HSNLF)(1)-0213, was tested in two dimensional wind tunnels to investigate the performance of the basic airfoil shape. A three dimensional wing designed with this airfoil and a high lift flap system is also being evaluated with a full size, half span model.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 3; p 697-726
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  • 68
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    Design and test of a natural laminar flow/large Reynolds number airfoil with a high design cruise lift coefficient (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Research activity on an airfoil designed for a large airplane capable of very long endurance times at a low Mach number of 0.22 is examined. Airplane mission objectives and design optimization resulted in requirements for a very high design lift coefficient and a large amount of laminar flow at high Reynolds number to increase the lift/drag ratio and reduce the loiter lift coefficient. Natural laminar flow was selected instead of distributed mechanical suction for the measurement technique. A design lift coefficient of 1.5 was identified as the highest which could be achieved with a large extent of laminar flow. A single element airfoil was designed using an inverse boundary layer solution and inverse airfoil design computer codes to create an airfoil section that would achieve performance goals. The design process and results, including airfoil shape, pressure distributions, and aerodynamic characteristics are presented. A two dimensional wind tunnel model was constructed and tested in a NASA Low Turbulence Pressure Tunnel which enabled testing at full scale design Reynolds number. A comparison is made between theoretical and measured results to establish accuracy and quality of the airfoil design technique.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA, Langley Research Center, Research in Natural Laminar Flow and Laminar-Flow Control, Part 3; p 727-751
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  • 69
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    Design of the low-speed NLF(1)-0414F and the high-speed HSNLF(1)-0213 airfoils with high-lift systems (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: The design and testing of Natural Laminar Flow (NLF) airfoils is examined. The NLF airfoil was designed for low speed, having a low profile drag at high chord Reynolds numbers. The success of the low speed NLF airfoil sparked interest in a high speed NLF airfoil applied to a single engine business jet with an unswept wing. Work was also conducted on the two dimensional flap design. The airfoil was decambered by removing the aft loading, however, high design Mach numbers are possible by increasing the aft loading and reducing the camber overall on the airfoil. This approach would also allow for flatter acceleration regions which are more stabilizing for cross flow disturbances. Sweep could then be used to increase the design Mach number to a higher value also. There would be some degradation of high lift by decambering the airfoil overall, and this aspect would have to be considered in a final design.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 3; p 637-671
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  • 70
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    Wind tunnel results of the low-speed NLF(1)-0414F airfoil (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: The large performance gains predicted for the Natural Laminar Flow (NLF)(1)-0414F airfoil were demonstrated in two-dimensional airfoil tests and in wind tunnel tests conducted with a full scale modified Cessna 210. The performance gains result from maintaining extensive areas of natural laminar flow, and were verified by flight tests conducted with the modified Cessna. The lift, stability, and control characteristics of the Cessna were found to be essentially unchanged when boundary layer transition was fixed near the wing leading edge. These characteristics are very desirable from a safety and certification view where premature boundary layer transition (due to insect contamination, etc.) must be considered. The leading edge modifications were found to enhance the roll damping of the Cessna at the stall, and were therefore considered effective in improving the stall/departure resistance. Also, the modifications were found to be responsible for only minor performance penalties.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 3; p 673-696
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  • 71
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    Numerical experiments on transition control in wall-bounded shear flows (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Results are presented from a numerical simulation of transition control in plane channel and boundary layer flows. The analysis is based on a pseudo-spectral/finite difference semi-implicit solution procedure employed to numerically integrate the time-dependent, three-dimensional, incompressible Navier-Stokes equations in a doubly periodic domain. In the channel flow, it was found that the active periodic suction/blowing method was effective in controlling strongly three-dimensional disturbances. In the boundary layer, the preliminary analysis indicated that in the early stages, passive control by suction is as effective as active control to suppress instabilities. The current work is focused on a detailed comparison of active and passive control by suction/blowing in the boundary layer.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA, Langley Research Center, Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 577-592
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  • 72
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    Application of sound and temperature to control boundary-layer transition (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: The growth and decay of a wave packet convecting in a boundary layer over a concave-convex surface and its active control by localized surface heating are studied numerically using direct computations of the Navier-Stokes equations. The resulting sound radiations are computed using linearized Euler equations with the pressure from the Navier-Stokes solution as a time-dependent boundary condition. It is shown that on the concave portion the amplitude of the wave packet increases and its bandwidth broadens while on the convex portion some of the components in the packet are stabilized. The pressure field decays exponentially away from the surface and then algebraically, exhibiting a decay characteristic of acoustic waves in two dimensions. The far-field acoustic behavior exhibits a super-directivity type of behavior with a beaming downstream. Active control by surface heating is shown to reduce the growth of the wave packet but have little effect on acoustic far field behavior for the cases considered. Active control by sound emanating from the surface of an airfoil in the vicinity of the leading edge is experimentally investigated. The purpose is to control the separated region at high angles of attack. The results show that injection of sound at shedding frequency of the flow is effective in an increase of lift and reduction of drag.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 593-616
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  • 73
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    Theoretical methods and design studies for NLF and HLFC swept wings at subsonic and supersonic speeds (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Laminarization of the boundary layer on the surface of aircraft wings can be accomplished by the use of concepts such as Natural Laminar Flow (NLF), Laminar-Flow Control (LFC), and Hybrid Laminar-Flow Control (HLFC). Several integral boundary-layer methods were developed for the prediction of laminar, transition, and separating turbulent boundary layers. These methods were developed for use at either subsonic or supersonic speeds, have small computer execution times, and are simple to use. The theoretical equations and assumptions which form the basis of the boundary-layer method, are briefly outlined and the results of several correlation cases with exciting experimental data are presented.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 547-575
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  • 74
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    Numerical solutions of the compressible 3-D boundary-layer equations for aerospace configurations with emphasis on LFC (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: The application of stability theory in Laminar Flow Control (LFC) research requires that density and velocity profiles be specified throughout the viscous flow field of interest. These profile values must be as numerically accurate as possible and free of any numerically induced oscillations. Guidelines for the present research project are presented: develop an efficient and accurate procedure for solving the 3-D boundary layer equation for aerospace configurations; develop an interface program to couple selected 3-D inviscid programs that span the subsonic to hypersonic Mach number range; and document and release software to the LFC community. The interface program was found to be a dependable approach for developing a user friendly procedure for generating the boundary-layer grid and transforming an inviscid solution from a relatively coarse grid to a sufficiently fine boundary-layer grid. The boundary-layer program was shown to be fourth-order accurate in the direction normal to the wall boundary and second-order accurate in planes parallel to the boundary. The fourth-order accuracy allows accurate calculations with as few as one-fifth the number of grid points required for conventional second-order schemes.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 517-545
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  • 75
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    Sensitivity of LFC techniques in the non-linear regime (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: For all the Laminar Flow Control (LFC) techniques examined, finite-amplitude effects are destabilizing, i.e., finite-amplitude 2-D Tollmien-Schlichting (TS) waves grow faster than predicted by linear theory. It was also found, in direct contrast to the results from linear theory for low-amplitude waves, that temperature fluctuations exert a further destabilizing influence on finite amplitude 2-D TS waves. The controlled boundary layers are, of course, subject to intense 3-D secondary instabilities. The instantaneous growth rates of both the fundamental and subharmonic instabilities are strongly tied to the amplitude of the primary 2-D wave. The principal finite-amplitude effects upon the 3-D secondary instabilities occur through the faster growth of the 2-D waves.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 491-516
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  • 76
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    Boundary-layer stability analysis of Langley Research Center 8-foot LFC experimental data (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: An analytical study of linear-amplifying instabilities of a laminar boundary layer as found in the experimental data of the LaRC/8-foot laminar-flow control (LFC) experiment was completed and the results are presented. The LFC airfoil used for this experiment was a swept, supercritical design which removed suction air through spanwise slots. The amplification of small disturbances by linear processes on a swept surface such as this can be due to either Tollmien-Schlichting (TS) and/or crossflow (CF) mechanisms. This study consists of the examination of these two instabilities by both the commonly used incompressible (SALLY and MARIA) analysis and the more involved compressible (COSAL) analysis. A wide range of experimental test conditions with variations in Mach number, Reynolds number, and suction distributions were available for this study. Experimentally determined transition locations were found from thin-film techniques and were used to correlate the n-factors at transition for the range of test cases.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 471-489
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  • 77
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    An experimental evaluation of slots versus porous strips for laminar-flow applications (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Detailed mean velocity and disturbance amplitude measurements were conducted in a Blasius boundary-layer flow with wall suction applied at three downstream locations. The main emphasis was a direct comparison of the growth rate of the instability wave with discrete spanwise slots versus wide porous strips. The results demonstrate that the local effects of suction through slots or very narrow porous strips have a greater beneficial effect on the stability of the boundary-layer flow relative to the suction influence of a wide porous strip. Codes which use continuous suction for the growth rates of the instability waves to determine the suction quantities for a multiple series of slots will be quite conservative in the estimation of the suction quantity. Guidelines were provided for suction-chamber design and flow rates to minimize internal oscillations which propagate into the boundary-layer flow.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA, Langley Research Center, Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 435-451
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  • 78
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    Results of LFC experiment on slotted swept supercritical airfoil in Langley's 8-foot transonic pressure tunnel (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: A large chord swept supercritical laminar-flow control (LFC) airfoil was designed, constructed, and tested in the Langley 8-foot Transonic Pressure Tunnel (TPT). The LFC airfoil experiment was established to provide basic information concerning the design and compatibility of high performance supercritical airfoils with suction boundary-layer control achieved through fine slots or porous surface concepts. Shockless pressure distribution was achieved. Full chord laminar flow was achieved on upper and lower surfaces. Full chord laminar flow was maintained at subcritical speeds and over large supercritical zones. Feasibility of combined suction laminarization and supercritical airfoil technology was demonstrated.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 453-469
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  • 79
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    Experimental studies on Goertler vortices (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Goertler vortices arise in laminar boundary layers along concave walls due to an imbalance between pressure and centrifugal forces. In advanced laminar-flow control (LFC) supercritical airfoil designs, boundary-layer suction is primarily used to control Tollmien-Schlichting instability and cross-flow vortices in the concave region near the leading edge of the airfoil lower surface. The concave region itself is comprised of a number of linear segments positioned to limit the total growth of Goertler vortices. Such an approach is based on physical reasonings but rigorous theoretical justification or experimental evidence to support such an approach does not exist. An experimental project was initiated at NASA Langley to verify this concept. In the first phase of the project an experiment was conducted on an airfoil whose concave region has a continuous curvature distribution. Some results of this experiment were previously reported and significant features are summarized.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 421-433
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  • 80
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    Predicted and hot-film measured Tollmien-Schlichting wave characteristics (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: The Tollmien-Schlichting (TS) instability is a time-dependence instability which can lead to transition of laminar boundary layers on airfoils. A comparison of theoretical predictions and experimental observations of the TS instability on the NLF(1)-0414F airfoil designed by Viken and Pfenninger. The theoretical predictions were obtained using the SALLY stability code. Test results, from the same hot films that were used to detect transition, revealed that TS waves could be detected by the hot films if the hot-film signal was adequately modified.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 377-380
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  • 81
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    Flow quality measurements in compressible subsonic flows (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: The purpose is to re-examine the heat transfer from a hot-wire probe in the compressible subsonic flow regime; describe the three-wire hot-wire probe calibration and data reduction techniques used to measure the velocity, density, and total temperature fluctuation; and present flow quality results obtained in the Langley 0.3 meter Transonic Cryogenic Wind Tunnel and in flight with the NASA JetStar from the same three-wire hot-wire probe.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 345-357
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  • 82
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    Effect of roughness on the stability of boundary layers (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: An analysis is conducted on the effect of imperfections consisting of humps and dips on the stability of incompressible flows over flat plates. The mean flow is calculated using interacting boundary layers. Linear quasiparallel spatial stability is used to calculate the growth rates and mode shapes of two-dimensional disturbances. Then, the amplification factor is computed. A search for the most dangerous frequency is conducted based on an amplification factor of 9 in the shortest distance. Correlations are made with the transition experiment of Walker and Greening using the e sup 9 method.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA, Langley Research Center, Research in Natural Laminar Flow and Laminar-Flow Control, Part 1; p 301-315
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  • 83
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    Advanced measurement techniques, part 1 (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: In modern laminar flow flight and wind tunnel research, it is important to understand the specific cause(s) of laminar to turbulent boundary layer transition. Such information is crucial to the exploration of the limits of practical application of laminar flow for drag reduction on aircraft. The process of transition involves both the possible modes of disturbance growth, and the environmental conditioning of the instabilities by freestream or surface conditions. The possible modes of disturbance growth include viscous, inviscid, and modes which may bypass these natural ones. Theory provides information on the possible modes of disturbance amplification, but experimentation must be relied upon to determine which of those modes actually dominates the transition process in a given environment. The results to date of research on advanced devices and methods used for the study of transition phenomena in the subsonic and transonic flight and wind tunnel environments are presented.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 317-340
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  • 84
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    Goertler instability on an airfoil (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: An effective computational scheme was developed to study the growth/damping of Goertler vortices along walls of variable curvature. Computational experiments indicate that when the amplification rates for the u-, v-, and w-perturbations are the same, the finite difference approach to solve the initial value problem and the normal mode approach give identical results for the Blasius boundary layer on constant curvature concave walls. The growth of Goertler vortices was rapid in the concave regions and was followed by sharp damping in the convex region. However, multiple sets of counter-rotating vortices were formed and remained far downstream in the convex region. The current computational scheme can be easily extended to more realistic problems including variable pressure gradients and suction effects.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 1; p 289-300
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  • 85
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    Interaction of Tollmien-Schlichting waves and Goertler vortices (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: There are many fluid flows of practical interest where transition can be caused by competing hydrodynamic instabilities. Thus in three-dimensional boundary-layer flows over curved walls, instability might be caused by Tollmien-Schlichting waves, Goertler vortices or crossflow vortices. If a particular type of instability is suppressed by some means, there is the possibility that another one might be stimulated. Hence it is important to understand the mechanisms by which these different instabilities interact. Some properties of the interaction which can take place between Goertler vortices and Tollmien-Schlichting waves are discussed.
    Schlagwort(e): AERODYNAMICS
    Materialart: Research in Natural Laminar Flow and Laminar-Flow Control, Part 1; p 261-271
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  • 86
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    Boundary-layer receptivity and laminar-flow airfoil design (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Boundary-layer receptivity examines the way in which external disturbances generate instability waves in boundary layers. Receptivity theory is complementary to stability theory, which studies the evolution of disturbances that are already present in the boundary layer. A transition prediction method which combines receptivity with linear stability theory would directly account for the influence of free-stream disturbances and also consider the characteristics of the boundary layer upstream of the neutral stability point. The current e sup N transition prediction methods require empirical correlations for the influence of environmental disturbances, and totally ignore the boundary layer characteristics upstream of the neutral stability point. The regions where boundary-layer receptivity occurs can be separated into two classes, one near the leading edges and the other at the downstream points where the boundary layer undergoes rapid streamwise adjustments. Analyses were developed for both types of regions, and parametric studies which examine the relative importance of different mechanisms were carried out. The work presented here has focused on the low Mach number case. Extensions to high subsonic and supersonic conditions are presently underway.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA, Langley Research Center, Research in Natural Laminar Flow and Laminar-Flow Control, Part 1; p 273-287
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  • 87
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    Stability theory applications to laminar-flow control (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: In order to design Laminar Flow Control (LFC) configurations, reliable methods are needed for boundary-layer transition predictions. Among the available methods, there are correlations based upon R sub e, shape factors, Goertler number and crossflow Reynolds number. The most advanced transition prediction method is based upon linear stability theory in the form of the e sup N method which has proven to be successful in predicting transition in two- and three-dimensional boundary layers. When transition occurs in a low disturbance environment, the e sup N method provides a viable design tool for transition prediction and LFC in both 2-D and 3-D subsonic/supersonic flows. This is true for transition dominated by either TS, crossflow, or Goertler instability. If Goertler/TS or crossflow/TS interaction is present, the e sup N will fail to predict transition. However, there is no evidence of such interaction at low amplitudes of Goertler and crossflow vortices.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA, Langley Research Center, Research in Natural Laminar Flow and Laminar-Flow Control, Part 1; p 219-244
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  • 88
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    Nonparallel stability of boundary layers (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: The asymptotic formulations of the nonparallel linear stability of incompressible growing boundary layers are critically reviewed. These formulations can be divided into two approaches. The first approach combines a numerical method with either the method of multiple scales, or the method of averaging, of the Wentzel-Kramers-Brillouin (WKB) approximation; all these methods yield the same result. The second approach combined a multi-structure theory with the method of multiple scales. The first approach yields results that are in excellent agreement with all available experimental data, including the growth rates as well as the neutral stability curve. The derivation of the linear stability of the incompressible growing boundary layers is explained.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA, Langley Research Center, Research in Natural Laminar Flow and Laminar-Flow Control, Part 1; p 245-259
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  • 89
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    Laminar flow: The Cessna perspective (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: A review of Natural Laminar Flow (NLF) and Laminar-Flow Control activities over the last twenty years at the Cessna Aircraft Company is presented. Expected NLF benefits and remaining challenges are then described.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA, Langley Research Center, Research in Natural Laminar Flow and Laminar-Flow Control, Part 1; p 79-88
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  • 90
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    The right wing of the LEFT airplane (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: The NASA Leading-Edge Flight Test (LEFT) program addressed the environmental issues which were potential problems in the application of Laminar Flow Control (LFC) to transport aircraft. These included contamination of the LFC surface due to dirt, rain, insect remains, snow, and ice, in the critical leading-edge region. Douglas Aircraft Company designed and built a test article which was mounted on the right wing of the C-140 JetStar aircraft. The test article featured a retractable leading-edge high-lift shield for contamination protection and suction through perforations on the upper surface for LFC. Following a period of developmental flight testing, the aircraft entered simulated airline service, which included exposure to airborne insects, heavy rain, snow, and icing conditions both in the air and on the ground. During the roughly 3 years of flight testing, the test article has consistently demonstrated laminar flow in cruising flight. The experience with the LEFT experiment was summarized with emphasis on significant test findings. The following items were discussed: test article design and features; suction distribution; instrumentation and transition point reckoning; problems and fixes; system performance and maintenance requirements.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA, Langley Research Center, Research in Natural Laminar Flow and Laminar-Flow Control, Part 1; p 141-161
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  • 91
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    Lockheed laminar-flow control systems development and applications (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Progress is summarized from 1974 to the present in the practical application of laminar-flow control (LFC) to subsonic transport aircraft. Those efforts included preliminary design system studies of commercial and military transports and experimental investigations leading to the development of the leading-edge flight test article installed on the NASA JetStar flight test aircraft. The benefits of LFC on drag, fuel efficiency, lift-to-drag ratio, and operating costs are compared with those for turbulent flow aircraft. The current activities in the NASA Industry Laminar-Flow Enabling Technologies Development contract include summaries of activities in the Task 1 development of a slotted-surface structural concept using advanced aluminum materials and the Task 2 preliminary conceptual design study of global-range military hybrid laminar flow control (HLFC) to obtain data at high Reynolds numbers and at Mach numbers representative of long-range subsonic transport aircraft operation.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA, Langley Research Center, Research in Natural Laminar Flow and Laminar-Flow Control, Part 1; p 53-77
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  • 92
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    Laminar flow: Challenge and potential (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Commercial air transportation has experienced revolutionary technology advances since WWII. These technology advances have resulted in an explosive growth in passenger traffic. Today, however, many technologies have matured, and maintaining a similar growth rate will be a challenge. A brief history of laminar flow technology and its application to subsonic and supersonic air transportation is presented.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA, Langley Research Center, Research in Natural Laminar Flow and Laminar-Flow Control, Part 1; p 25-44
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  • 93
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    Reduction of tilt rotor download using circulation control (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: The effect of boundary layer control blowing on the download of a wing in the wake of a hovering rotor was measured in a small scale experiment. The objective was to evaluate the potential of boundary layer control blowing for reducing tilt rotor download. Variations were made in rotor thrust coefficient, blowing pressure ratio, and blowing slot height. The effect of these parameter variations on the wing download and wing surface pressures is presented. The boundary layer control blowing caused reductions in the wing download of 25 to 55 percent.
    Schlagwort(e): AERODYNAMICS
    Materialart: Proceedings of the Circulation-Control Workshop, 1986; p 429-447
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  • 94
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    An aerodynamic comparison of blown and mechanical high lift airfoils (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Short takeoff and landing (STOL) performance utilizing a circulation control airfoil was successfully demonstrated on the A-6 CCW (circulation control wing). Controlled flight at speeds as slow as 67 knots was demonstrated. Takeoff ground run and liftoff speed reductions in excess of 40 and 20 percent respectively were achieved. Landing ground roll and approach speeds were similarly reduced. The technology demonstrated was intended to be useable on modern high performance aircraft. STOL performance would be achieved through the combination of a 2-D vectored nozzle and a circulation control type of high lift system. The primary objective of this demonstration was to attain A-6 CCW magnitude reductions in takeoff and landing flight speed and ground distance requirements using practical bleed flow rates from a modern turbofan engine for the blown flap system. Also, cruise performance could not be reduced by the wing high lift system. The A-6 was again selected as the optimum demonstration vehicle. The procedure and findings of the study to select the optimum high lift wing design are documented. Some findings of a supercritical airfoil and a comparison of 2-D and 3-D results are also described.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA. Ames Research Center Proceedings of the Circulation-Control Workshop, 1986; p 449-477
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  • 95
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    Analysis of a fixed-pitch X-wing rotor employing lower surface blowing (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Lower surface blowing (LSB) is investigated as an alternative to the variable blade pitch requirement for the X-wing Circulation Control (CC) rotor concept. Addition trailing edge blowing slots on the lower surfaces of CC airfoils provide a bidirectional lift capability that effectively doubles the control range. The operational requirements of this rotor system are detailed and compared to the projected performance attributes of LSB airfoils. Analysis shows that, aerodynamically, LSB supplies a fixed pitch rotor system with the equivalent lift efficiency and rotor control of present CC rotor designs that employ variable blade pitch. Aerodynamic demands of bidirectional lift production are predicted to be within the capabilities of current CC airfoil design methodology. Emphasis in this analysis is given to the high speed rotary wing flight regime unique to stoppable rotor aircraft. The impact of a fixed pitch restriction in hover and low speed flight is briefly discussed.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA. Ames Research Center Proceedings of the Circulation-Control Workshop, 1986; p 363-380
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  • 96
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    Pressure distributions and oil-flow patterns for a swept circulation-control wing (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Pressure distributions and photographs of oil flow patterns are presented for a circulation control wing. The model was an aspect ratio four semispan wing mounted on the side wall of the NASA Ames Transonic Wind Tunnel. The airfoil was a 20 percent thick ellipse, modified with circular leading and trailing edges of 4 percent radius, and had a 25.4 cm constant chord. This configuration does not represent a specific wing design, but is generic. A full span, tangetial, rearward blowing, circulation control slot was incorporated ahead of the trailing edge on the upper surface. The wing was tested at Mach numbers from 0.3 to 0.75 at sweep angle of 0 to 45 deg with internal to external pressure ratios of 1.0 to 3.0. Lift and pitching momemt coefficients were obtained from measured pressure distributions at five span stations. When the conventional corrections resulting from sweep angle are applied to the lift and moment of circulation control sections, no additional corrections are necessary to account for changes in blowing efficiency. This is demonstrated for an aft sweep angle of 45 deg. An empirical technique for estimating the downwash distribution of a swept wing was validated.
    Schlagwort(e): AERODYNAMICS
    Materialart: Proceedings of the Circulation-Control Workshop, 1986; p 209-238
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  • 97
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    Turbulence modeling (1987)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: Recent developments at several levels of statistical turbulence modeling applicable to aerodynamics are briefly surveyed. Emphasis is on examples of model improvements for transonic, two-dimensional flows. Experience with the development of these improved models is cited to suggest methods of accelerating the modeling process necessary to keep abreast of the rapid movement of computational fluid dynamics into the computation of complex three-dimensional flows.
    Schlagwort(e): AERODYNAMICS
    Materialart: Supercomputing in Aerospace; p 221-238
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  • 98
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    Numerical simulation of unsteady viscous flows (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Most unsteady viscous flows may be grouped into two categories, i.e., forced and self-sustained oscillations. Examples of forced oscillations occur in turbomachinery and in internal combustion engines while self-sustained oscillations prevail in vortex shedding, inlet buzz, and wing flutter. Numerical simulation of these phenomena was achieved due to the advancement of vector processor computers. Recent progress in the simulation of unsteady viscous flows is addressed.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA. Ames Research Center, Supercomputing in Aerospace; p 257-267
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  • 99
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    Integration of communications and tracking data processing simulation for space station (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: A simplified model of the communications network for the Communications and Tracking Data Processing System (CTDP) was developed. It was simulated by use of programs running on several on-site computers. These programs communicate with one another by means of both local area networks and direct serial connections. The domain of the model and its simulation is from Orbital Replaceable Unit (ORU) interface to Data Management Systems (DMS). The simulation was designed to allow status queries from remote entities across the DMS networks to be propagated through the model to several simulated ORU's. The ORU response is then propagated back to the remote entity which originated the request. Response times at the various levels were investigated in a multi-tasking, multi-user operating system environment. Results indicate that the effective bandwidth of the system may be too low to support expected data volume requirements under conventional operating systems. Instead, some form of embedded process control program may be required on the node computers.
    Schlagwort(e): COMMUNICATIONS AND RADAR
    Materialart: NASA. Lyndon B.; NASA. Lyndon B. John
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    Investigation of dynamic ground effect (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: An experimental investigation of dynamic ground effect was conducted in the Univ. of Kansas wind tunnel using delta wings of 60, 70, 75 deg sweep; the XB-70 wing; and the F-104A wing. Both static and dynamic tests were made. Test data were compared to other test data, including dynamic flight test data of the XB-70 and F-104A. Limited flow visualization test were conducted. A significant dynamic effect was found for highly swept delta wings.
    Schlagwort(e): AERODYNAMICS
    Materialart: NASA. Ames Research Center Proceedings of the 1985 NASA Ames Research Center's Ground-Effects Workshop; p 363-393
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