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  • 1990-1994  (7)
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  • 1
    Publication Date: 2014-09-25
    Description: Meteoritic ablation in the upper atmosphere is the commonly accepted source of the mesospheric metals between 80 and 105 km. The vertical and temporal behavior of some of these metals can be probed with high accuracy and resolution using resonance fluorescence lidar techniques. Of considerable interest in recent years has been the sporadic and rapid formation of thin, dense enhancements in these metallic layers. Since late Mar. 1991, the UIUC CEDAR lidar system, located at the Urbana Atmospheric Observatory, has been routinely operating at the Fe resonance line of 372 nm in order to probe the mesospheric Fe layer. In Nov. 1991, the capability to investigate mesospheric Ca(+) at the resonance line of 393.4 nm was added. The lidar's eximer-pumped dye laser uses Exciton QUI laser dye dissolved in p-dioxane, which can lase at both the Fe and Ca(+) frequencies. Various aspects of this investigation are discussed.
    Keywords: GEOPHYSICS
    Type: NASA. Langley Research Center, Sixteenth International Laser Radar Conference, Part 1; p 309-312
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  • 2
    Publication Date: 2019-06-28
    Description: The possible profiles of high subsonic speed airfoils with extensive regions of natural laminar flow (NLF) are explored, on the bases of calculations which suggest that high subsonic Mach number NLFs are obtainable for both swept and unswept wing applications at certain Reynolds numbers. Attention is given to the transonic pressure distributions of airfoils for unswept wings at freestream Mach numbers of 0.65-0.80 and chord Reynolds numbers of up to 50 million. The case of 10-30 deg swept-wing NLF airfoils is also investigated for chord Reynolds numbers of 15-50 million.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-1773
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  • 3
    Publication Date: 2014-09-25
    Description: Four-frequency lidar measurements of temperature and wind velocity require accurate frequency tuning to an absolute reference and long term frequency stability. We quantify frequency tuning errors for the Illinois sodium system, to measure absolute frequencies and a reference interferometer to measure relative frequencies. To determine laser tuning errors, we monitor the vapor cell and interferometer during lidar data acquisition and analyze the two signals for variations as functions of time. Both sodium cell and interferometer are the same as those used to frequency tune the laser. By quantifying the frequency variations of the laser during data acquisition, an error analysis of temperature and wind measurements can be calculated. These error bounds determine the confidence in the calculated temperatures and wind velocities.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: NASA. Langley Research Center, Sixteenth International Laser Radar Conference, Part 1; p 317-320
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  • 4
    Publication Date: 2019-07-27
    Description: To simplify the design of swept supercritical (SC) Laminar Flow Control (LFC) wings and maintain satisfactory low speed characteristics, blunt-nosed swept SC LFC wings without nose flaps and lower wing loadings were studied. Their boundary layer crossflow in the leading edge area is optimally controlled (1) by compensating the boundary layer crossflow of the front acceleration zone by an opposite crossflow in a downstream pressure rise area, (2) by maintaining a neutrally stable boundary layer crossflow by suction within a narrow spanwise suction strip located close to the wing attachment line in the front acceleration zone. The required suction massflow and power are then very small, especially considering the strongly stabilizing effect of surface and streamline curvature on crossflow stability.
    Keywords: AERODYNAMICS
    Type: IUTAM Symposium on Laminar-Turbulent Transition; Sept. 11-15, 1989; Toulouse; France
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  • 5
    Publication Date: 2019-07-27
    Description: Studies on supersonic long-range LFC (laminar flow control) aircraft were performed with the aim of maximizing L/D and alleviating sonic boom during supersonic cruise. It is found that configurations with highly swept LFC wings of very high structural aspect ratio, with the sweep increasing toward the wing root and braced externally by wide chord laminarized struts, appear especially promising. In the supersonic cruise design condition the wing upper surface isobars are swept such that the flow in the direction normal to them is transonic with embedded supersonic zones and practically shock-free over most of the span, with M-perpendicular equal to the two-dimensional design values of advanced SC LFC airfoils, e.g., of the X-787 or X-6 type.
    Keywords: AERODYNAMICS
    Type: ICAS Congress; Sept. 9-14, 1990; Stockholm; Sweden
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  • 6
    Publication Date: 2019-07-27
    Description: This paper provides an overview of the status of supersonic laminar flow control. Existing research into the aerodynamic problems of subsonic and supersonic laminar flow control is first reviewed to provide a prospective for subsequent discussions of recent studies to evaluate the potential performance benefits of the application of laminar flow control to supersonic transports. A flight research program to provide a realistic assessment of the technical feasibility is then described.
    Keywords: AERODYNAMICS
    Type: ICAS Congress; Sept. 9-14, 1990; Stockholm; Sweden
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  • 7
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    In:  Other Sources
    Publication Date: 2019-07-12
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 27; 204-210
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