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  • 1
    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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    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
    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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    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
    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
    Publikationsdatum: 2011-08-19
    Beschreibung: Tabulations are presented for the proper elements of 1227 higher accuracy orbits of faint minor planets encompassing earth and deep Mars crossers, Trojans, and Hildas. The distribution of the closest approach distance to Mars drops off sharply near zero, while that for Jupiter vanishes near 1.1 AU; it is suggested that Mars and Jupiter have caused these boundaries, so that the asteroid belt must have been larger early in the solar system's history. Some 3.5 percent of the sample, primarily shallow crossers, can impact Mars; the fortuitous alignments required for impact occur with near-simultaneity for these objects, so that they will episodically bombard Mars.
    Schlagwort(e): ASTRONOMY
    Materialart: Icarus (ISSN 0019-1035); 72; 276-303
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  • 7
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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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  • 8
    Publikationsdatum: 2011-08-19
    Beschreibung: Analysis of the color distribution of OH/IR stars and IRAS low-resolution spectra class 30 objects suggests the presence of a well-defined evolutionary sequence which is populated by late asymptotic giant branch (LAGB) stars. The paper reports ground-based identification and infrared photometry of 10 candidates of news LAGB stars. None of the selected sources are found to have optical counterparts, and eight of the 10 show a strong 10-micron silicate absorption feature. It is suggested that these stars represent an invisible extension of extreme Mira variables and are some of the most evolved stars observed to date.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 321; 975-983
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  • 9
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    Publikationsdatum: 2011-08-19
    Beschreibung: By working in the Fourier plane, approximate removal of stripe artifacts in IRAS images can be effected. The image of interest is smoothed and subtracted from the original, giving the high-spatial-frequency part. This 'filtered' image is then clipped to remove point sources and then Fourier transformed. Subtracting the Fourier components contributing to the stripes in this image from the Fourier transform of the original and transforming back to the image plane yields substantial removal of the stripes.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal (ISSN 0004-6256); 94; 1092-109
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  • 10
    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 296-302
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  • 11
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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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  • 12
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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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  • 13
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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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  • 14
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    Publikationsdatum: 2011-08-19
    Beschreibung: A table is presented which permits rapid determination of the constellation in which an object is located from its 1875.0 position. Directions for accessing and using the table are given. The historical background to the table's development is briefly stated.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 99
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  • 15
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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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  • 16
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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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    Publikationsdatum: 2011-08-19
    Beschreibung: An uncertainty analysis is conducted for four asteroids with different optical and radar observation histories in order to ascertain the degree to which near-earth asteroid ephemerides can be improved by means of radar observations. For any given set of optical and radar observations and their associated errors, the angular and earth-asteroid distance uncertainties are calculated as functions of time through 2001. The radar data furnished only a small absolute improvement in such cases as that of 1627 Ivar, where a long history of optical astrometric data exists, but dramatic reductions in ephemeris uncertainties are obtainable for asteroids having only short optical data histories.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal (ISSN 0004-6256); 94; 189-200
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  • 18
    Publikationsdatum: 2011-08-19
    Beschreibung: The operational Multichannel Astrometric Photometer (MAP) now in use in the Allegheny Observatory astrometric program is the culmination of a decade of design and development effort. A detailed description of the system and its related software is followed by analysis of data acquired in four stellar regions. The study indicates an accuracy (in the sense of conformity to the best model), per night, for stars of the eighth magnitude or brighter, of 0.003 arcsec or better. These data points each have approximately twice the precision of the annual normal points obtained in our photographic program. Accuracy is shown to depend on: (1) the photon-count rate of the target star (it follows that the number of photons from the reference frame is also in important factor), (2) the duration of the observation, (3) the angular size of the reference frame, and (4) the quality of the astronomical seeing. Since (4) and, to a lesser extent, (1) involve the atmospheric characteristics at the time of observation, the probable performance at more favorable sites is discussed briefly.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal (ISSN 0004-6256); 94; 213-224
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  • 19
    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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  • 20
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    Publikationsdatum: 2011-08-19
    Beschreibung: The General Uranus Satellite Theory GUST (Laskar, 1986) is used for the construction of an analytical ephemeris for the Uranian satellites. The theory is fitted against earth-based observations from 1911 to 1986, and all radio and optical data obtained during Voyager encounter with Uranus. Earth-based observations alone allow the determination of masses which are within 15 percent of the values determined by the Uranus flyby. The analysis of all the observations confirm the values of the masses obtained during the encounter (Stone and Miner, 1986) and give a complete set of dynamical parameters for the analytical theory. An analytical ephemeris, GUST86, with an estimated precision of about 100 km with respect to Uranus is obtained.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 188; 1, De
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  • 21
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    Publikationsdatum: 2011-08-19
    Beschreibung: The rationale for a semipermanent all-sky X-ray monitor and a variety of options for its implementation are discussed. It is concluded that the Space Station offers an excellent opportunity for hosting such a monitor, and that a set of pinhole cameras can be configured to provide an effective and economical monitor system. A baseline of six independent pinhole modules, each of which requires approximately 1 cu ft, 30 pounds, 2 W and 100 bits per second, can provide full sky coverage with scientifically interesting sensitivities. No other resources or special accommodation (such as detailed alignment registration, time-tagging, or on-orbit servicing) would be required. The baseline system can locate bright sources to a few arcmin and can simultaneously measure each of the several hundred sources in the sky brighter than a few thousandths the intensity of the Crab nebula every day for decades.
    Schlagwort(e): ASTRONOMY
    Materialart: Space Science Reviews (ISSN 0038-6308); 45; 3-4,
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  • 22
    Publikationsdatum: 2011-08-19
    Beschreibung: The MIT High Resolution X-Ray Spectroscopy experiment on the AXAF, which will study physical conditions in celestial sources by means of detailed measurements of emission and absorption features in their spectra, involves two complementary dispersive instruments: Bragg Crystal Spectrometer (BCS) and High Energy Transmission Grating (HETG). This paper discusses the principles of operation of BCS and HETG and the results that will be obtained by these instruments. Measurements of individual line strengths obtained by the AXAF spectrometers will allow the application of plasma diagnostic techniques to a study of the detailed physical conditions in celestial objects, particularly in the optically thin plasma of supernova remnants, which is particularly well suited to the application of plasma diagnostics.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Letters and Communications (ISSN 0888-6512); 26; 1-2,
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  • 23
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    Publikationsdatum: 2011-08-19
    Beschreibung: This paper presents an overview of NASA's Advanced X-Ray Astrophysics Facility (AXAF), which is planned for launch in the 1990s and is expected to operate in space for at least 15 years. The design of the X-ray telescope is discussed and the instruments that may fly at the start of the AXAF mission, the principal investigator of each instrument, and the instrument performance parameters are listed. The AXAF instruments will include low-energy and high-energy transimission gratings, a Bragg crystal spectrometer, CCD imagers, an X-ray calorimeter, and a microchannel plate imager. The long lifetime of the AXAF will make it possible to follow up on the HEAO-2/Einstein results, the more recent X-ray observations performed by European and Japanese satellites, and the future ROSAT all-sky survey. The long lifetime of the AXAF, together with the servicing capability that will be offered by the Space Station, will also provide the opportunity of incorporating other instruments into the observatory.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Letters and Communications (ISSN 0888-6512); 26; 1-2,
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  • 24
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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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  • 25
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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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  • 26
    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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  • 27
    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 856-860
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  • 28
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    Publikationsdatum: 2011-08-19
    Beschreibung: An overview of large-scale plasma phenomena is presented based on results of spacecraft probing of comets Halley and Giacobini-Zinner and on worldwide submissions to the Large-Scale Phenomena Discipline Specialist Team of the International Halley Watch. Examples of tail phenomena and science are presented with emphasis on observed disconnection events. The archive of this material will clearly be very valuable for studying the comet/solar-wind interaction during the 1985-1986 apparition of Halley's comet.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 187; 1-2,
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  • 29
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    Publikationsdatum: 2011-08-19
    Beschreibung: Techniques and procedures employed to obtain data concerning the known asteroids from IRAS observations are discussed. The IRAS observations covered 95 percent of the sky with at least four scans of the telescope field of view. A search was first carried out for geometrical intersections of the trajectories of a given asteroid and the telescope boresight, following which a matched sighting was sought for each such intersection among the actual IRAS point source detections. By using ground based measurements of visual magnitudes, IRAS observations of IR brightness, and a thermal model, albedos and diameters have been computed for 1,822 known asteroids, increasing the amount of this kind of information by about an order of magnitude.
    Schlagwort(e): ASTRONOMY
    Materialart: Journal of the Astronautical Sciences (ISSN 0021-9142); 35; 287-299
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  • 30
    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: AIAA Journal (ISSN 0001-1452); 25; 1456-146
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  • 31
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: AIAA Journal (ISSN 0001-1452); 25; 1417
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  • 32
    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 385-393
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  • 33
    Publikationsdatum: 2011-08-19
    Beschreibung: The predictions of the two-layer models used to interpret radio spectra of the asteroids have been examined. It is clear that one must treat the models with caution as the physics is highly simplifed. Although the predictions are in accord with physical expectations, careful attention to the circumstances of the observations is essential. The lack of short-centimeter wavelength measurements of dielectric properties is especially vexing. Some simple improvements to the models based on studies of the lunar radio emission by Keihm and using radar measurements of asteroid surface characteristics by Ostro and colleagues are suggested. Even so, the calculation of a realistic continuum-emission spectrum for asteroidal bodies from 20 cm wavelength to 20 microns wavelength remains a formidable task.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 99; 1009-101
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  • 34
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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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  • 35
    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 673-679
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  • 36
    Publikationsdatum: 2011-08-19
    Beschreibung: Plasma analyzer data obtained by Pioneer 7 during its approach to about 12.1 million km from the nucleus of Comet P/Halley are presently interpreted as He(+) generated by charge exchange of the solar wind He(2+) with neutral cometary material. The maximum He(+) flux was detected several hours after the closest March 20, 1986 approach of the spacecraft, and is noted to be not only larger than expected, but also to exhibit large, discontinuous flux changes.
    Schlagwort(e): ASTRONOMY
    Materialart: Icarus (ISSN 0019-1035); 71; 192-197
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  • 37
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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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  • 38
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    Publikationsdatum: 2011-08-19
    Beschreibung: It is presently noted that, in some cases, the usually infeasible conduct of searches in gamma-ray astronomy can be rendered feasible by means of a time-smoothing technique that yields only a moderate sensitivity loss. The total observing time is subdivided into a convenient number m of subintervals, and summing the values of H of each of the subintervals. This will reduce the number of independent frequency values by a factor m due to the shorter observing time.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 175; 1-2,; 353
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  • 39
    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 109-114
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  • 40
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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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  • 41
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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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  • 42
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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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  • 43
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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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  • 44
    Publikationsdatum: 2011-08-19
    Beschreibung: Forty-three cold, dense molecular clouds are digitized from the Palomar Observatory Sky Survey glass plates and presented with epoch 1950.0 equatorial coordinates. Regardless of the cloud's extent, the digitized area is limited to a 23 arcmin square on the sky with pixel size of about 1.3 arcsec. The optical maps presented herein are useful for comparing complementary molecular cloud maps from radio or infrared instruments and can be obtained in FITS format for use on astronomical image-processing systems.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal Supplement Series (ISSN 0067-0049); 64; 127-129
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  • 45
    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 225-230
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  • 46
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    In:  Other Sources
    Publikationsdatum: 2011-08-19
    Beschreibung: Orbital elements are presented for the ten small satellites discovered by Voyager 2 at Uranus. These ten new satellites, whose provisional IAU designations are 1985UI and 1986UI through 1986U9, lie for the most part in equatorial, circular orbits; the most notable exception is 1986U8, the outer epsilon-ring shepherd, whose eccentricity e = 0.0101. Unlike the Voyager discoveries at Saturn, which included two co-orbiting satellites and three librators, the ten small Uranian satellites all have quite different semimajor axes.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Journal (ISSN 0004-6256); 93; 1268-127
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  • 47
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    In:  Other Sources
    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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  • 48
    Publikationsdatum: 2011-08-19
    Beschreibung: Surface brightness maps at 12, 25, 60, and 100 microns were made of a 2.5 deg x 2.5 deg area of the reflection nebulae in the Pleiades by coadding IRAS scans of this region. Emission is seen surrounding 17 Tau, 20 Tau, 23 Tau, and 25 Tau in all four bands, coextensive with the visible reflection nebulosity, and extending as far as 30 arcminutes from the illuminating stars. The infrared energy distributions of the nebulae peak in the 100 micron band, but up to 40 percent of the total infrared power lies in the 12 and 25 micron bands. The brightness of the 12 and 25 micron emission and the absence of temperature gradients at these wavelengths are inconsistent with the predictions of equilibrium thermal emission models. The emission at these wavelengths appears to be the result of micron nonequilibrium emission from very small grains, or from molecules consisting of 10-100 carbon atoms, which have been excited by ultraviolet radiation from the illuminating stars.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 313; 853-858
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  • 49
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    In:  Other Sources
    Publikationsdatum: 2011-08-19
    Beschreibung: Early astronomical photography of comets at perihelion encouraged the establishment of an International Halley Watch (IHW) Team for regularly photographing the Comet. The February 1986 period was particularly troublesome due to the limitations of cometary visibility in the Southern Hemisphere. Schmidt cameras were placed on Tahiti, Easter Island, Faraday Station on the Antarctic Peninsula, Reunion Island and in South Africa. Blue- and red-filter B/W images were obtained every night and color prints were occasionally shot. Each night's images were examined before the next night's photography. Several interesting anecdotes are recounted from shipping, manning and operation of the telescopes.
    Schlagwort(e): ASTRONOMY
    Materialart: Sky and Telescope (ISSN 0037-6604); 73; 258-263
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  • 50
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    In:  Other Sources
    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 481-488
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  • 51
    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Spacecraft and Rockets (ISSN 0022-4650); 24; 334-341
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  • 52
    Publikationsdatum: 2011-08-19
    Beschreibung: Several techniques useful in the analysis of data from coded-mask telescopes are presented. Methods of handling changes in the instrument pointing direction are reviewed and ways of using FFT techniques to do the deconvolution considered. Emphasis is on techniques for optimally-coded systems, but it is shown that the range of systems included in this class can be extended through the new concept of 'partial cycle averaging'.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 136; 2, Au; 337-349
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  • 53
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    In:  Other Sources
    Publikationsdatum: 2011-08-19
    Schlagwort(e): AERODYNAMICS
    Materialart: Journal of Aircraft (ISSN 0021-8669); 24; 518-522
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  • 54
    Publikationsdatum: 2011-08-19
    Beschreibung: The results from the X-ray observations of two BL Lacertae objects, H2155-304 and PKS0548-322, are presented. The observations were carried out with the HEAO-1 A2 Low Energy Detectors, the High Resolution Imager, and the Monitor Proportional Counter aboard the Einstein Observatory. Correlated X-ray intensity variations of about 20 percent in the 0.15-3.5 keV energy band and about 40 percent in the 1.5-10 keV energy band are observed in H2155-304 over a period of about 8 hr. A factor of two change in the intensity of PKS0548-322 in the 3.5-10 keV energy interval is also detected over a time interval of 1 hr. Variations in the X-ray intensity over a timescale of months and the hardening of the spectrum with increasing intensity are seen in the HEAO-1 A2 data on H2155-304. The shortest observed timescale for the variability is used to derive an upper limit on the mass of the central accreting source in the two BL Lac objects studied here.
    Schlagwort(e): ASTRONOMY
    Materialart: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 227; 525-534
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  • 55
    Publikationsdatum: 2013-08-31
    Beschreibung: The transformation portion of the Hubble Space Telescope (HST) Proposal Entry Processor System converts astronomer-oriented description of a scientific observing program into a detailed description of the parameters needed for planning and scheduling. The transformation system is one of a very few rulebased expert systems that has ever entered an operational phase. The day to day operations of the system and its rulebase are no longer the responsibility of the original developer. As a result, software engineering properties of the rulebased approach become more important. Maintenance issues associated with the coupling of rules within a rulebased system are discussed and a method is offered for partitioning a rulebase so that the amount of knowledge needed to modify the rulebase is minimized. This method is also used to develop a measure of the coupling strength of the rulebase.
    Schlagwort(e): ASTRONOMY
    Materialart: NASA, Goddard Space Flight Center, Proceedings of 1987 Goddard Conference on Space Applications of Artificial Intelligence (AI) and Robotics; p 1-1
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  • 56
    Publikationsdatum: 2013-08-31
    Beschreibung: Spectral observations of meteors have been carried out for several years using an optical electronics facility. Interest has centered on faint meteors and their trails in the period of intensive meteor showers. Over 800 meteors were registered during the observation period, with spectrograms obtained for 170 of these. A total of 86 meteors were photographed from two sites and for 25 of these spectrograms of the meteors as well as their trails were obtained. All meteors have undergone routine processing in order to determine atmospheric characteristics. Results are discussed.
    Schlagwort(e): ASTRONOMY
    Materialart: International Council of Scientific Unions, Middle Atmosphere Program. Handbook for MAP, Volume 25; p 410-415
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  • 57
    facet.materialart.
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    In:  CASI
    Publikationsdatum: 2013-08-31
    Beschreibung: The performance of a set of nonredundant arrays, that convert an existing telescope to an interferometer, was simulated. Each array is a perforated mask, placed at an image of the objective. Each pair of holes in a mask transmits a unique spatial frequency that is present in the target; hence the term nonredundant. Each mask produces a fringe I(f) in the focal plane that is the product of the Fourier transforms of the object and the optical transfer function S(f).
    Schlagwort(e): ASTRONOMY
    Materialart: NASA-Goddard Space Flight Center, Theoretical Problems in High Resolution Solar Physics, 2; p 143-144
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  • 58
    facet.materialart.
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    In:  CASI
    Publikationsdatum: 2013-08-31
    Beschreibung: Stellar spectra are analyzed to determine nonthermal processes for cool stars. A shock wave crossing model is supported by a study of the behavior of absorption and emission spectra. The shock waves are attributed to atmospheric kinetics. Circumstellar spectral lines are studied for information about gaseous circumstellar layers. The description of stellar envelopes is carried on through circumstellar dust. Characteristic properties of polarization in the dust are described in the case of specific stars, emphasizing narrowband observations in Mira, semiregular, and supergiant stars. Finally, the direct approach to measuring the angular diameters of stars and mapping the distribution of circumstellar dust and gas by lunar occultation or interferometry is discussed, using two prototype stars, an M supergiant and a dusty carbon star.
    Schlagwort(e): ASTRONOMY
    Materialart: NASA, Washington, The M-Type Stars; p 113-207
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  • 59
    facet.materialart.
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    In:  CASI
    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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  • 60
    Publikationsdatum: 2011-08-19
    Beschreibung: An atlas of 25 O3-B8 supergiant spectra in the wavelength ranges 1320-1580 A and 1620-1880 A is presented, based on high-resolution data from the IUE archives. The remarkably detailed relationship between the stellar-wind profiles and the optical spectral classifications throughout this sequence is emphasized. For instance, the (Si IV)/(C IV) ratio reverses between O4 and O6.5; and the B0, B0.5, and B0.7 Ia wind characteristics are each qualitatively unique and distinct from one another. The systematic behavior of nine stellar-wind features with ionization potentials ranging from 114 to 19 eV is summarized as a function of advancing spectral type.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 99; 40-53
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  • 61
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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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  • 62
    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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  • 63
    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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  • 64
    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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  • 65
    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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  • 66
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    In:  CASI
    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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  • 67
    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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  • 68
    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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  • 69
    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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  • 70
    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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  • 71
    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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  • 72
    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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  • 73
    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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  • 74
    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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  • 75
    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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  • 76
    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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  • 77
    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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  • 78
    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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  • 79
    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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  • 80
    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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  • 81
    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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  • 82
    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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  • 83
    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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  • 84
    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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  • 85
    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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  • 86
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    In:  CASI
    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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  • 87
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    In:  CASI
    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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  • 88
    facet.materialart.
    Unbekannt
    In:  CASI
    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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  • 89
    facet.materialart.
    Unbekannt
    In:  CASI
    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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  • 90
    facet.materialart.
    Unbekannt
    In:  CASI
    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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  • 91
    facet.materialart.
    Unbekannt
    In:  CASI
    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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  • 92
    facet.materialart.
    Unbekannt
    In:  CASI
    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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  • 93
    facet.materialart.
    Unbekannt
    In:  CASI
    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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  • 94
    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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  • 95
    facet.materialart.
    Unbekannt
    In:  CASI
    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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  • 96
    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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  • 97
    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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  • 98
    facet.materialart.
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    In:  CASI
    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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  • 99
    facet.materialart.
    Unbekannt
    In:  CASI
    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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  • 100
    facet.materialart.
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    In:  CASI
    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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