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  • 1
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    A 3-level Model for Schumann-Runge O2 Laser-Induced Fluorescence (1996)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: A three level model has been developed for the analysis of Schumann-Runge band (B(sup 3)Sigma(sup -)(sub u ) 〈- X(sup 3)Sigma(sup -)(sub g)) laser-induced fluorescence of molecular oxygen, O2. Such a model is required due to the severe lower state depletion which can occur when transitions having relatively large absorption cross-sections are excited. Such transitions are often utilized via ArF* or KrF* excimer or dye-laser excitation in high temperature environments. The rapid predissociation of the upper state prevents substantial repopulation of the lower state by collisional processes, and the lower state may be largely depleted, even at laser fluences as low as 10-100 mJ/sq cm. The resulting LIF signal in such cases no longer varies linearly with laser pulse energy, and the extent of the sublinear behavior varies with the particular rovibrational transition of interest. Relating the measured signal to the lower state population, then, necessitates the use of exceedingly low laser fluences. These low fluences in turn lead to the need to compromise spatial resolution in order to generate sufficient signal.
    Keywords: Lasers and Masers
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Observation of Vibrational Relaxation Dynamics in X(sup 3)Sigma(sup -)(sub g) Oxygen Following Stimulated Raman Excitation to the v=1 Level: Implications for the RELIEF Flow Tagging Technique (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The vibrational relaxation of ground-state molecular oxygen (O2, X(sup 3)Sigma(sup -)(sub g)) has been observed, following stimulated Raman excitation to the first excited vibrational level (v=1). Time delayed laser-induced fluorescence probing of the ro-vibrational population distribution was used to examine the temporal relaxation behavior. In the presence of water vapor, the relaxation process is rapid, and is dominated by near-resonant vibrational energy exchange between the v=1 level of O2 and the n2 bending mode of H2O. In the absence of H2O, reequilibration proceeds via homogeneous vibrational energy transfer, in which a collision between two v=1 O2 molecules leaves one molecule in the v=2 state and the other in the v=0 state. Subsequent collisions between molecules in v=1 and v〉1 result in continued transfer of population up the vibrational ladder. The implications of these results for the RELIEF flow tagging technique are discussed.
    Keywords: Inorganic, Organic and Physical Chemistry
    Type: AIAA Paper 96-0301 , 34th Aerospace Sciences Meeting and Exhibit; Jan 15, 1996 - Jan 18, 1996; Reno, NV; United States
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    NASA TECHNICAL REPORTS
  • 3
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    The NASA Langley Scramjet Test Complex (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The NASA Langley Scramjet Test Complex consists of five propulsion facilities which cover a wide spectrum of supersonic combustion ramjet (scramjet) test capabilities. These facilities permit observation of the effects on scramjet performance of speed and dynamic pressure from Mach 3.5 to near-orbital speeds, engine size from Mach 4 to 7, and test gas composition from Mach 4 to 7. In the Mach 3.5 to 8 speed range, the complex includes a direct-connect combustor test facility, two small-scale complete engine test facilities, and a large-scale complete engine test facility. In the hypervelocity speed range, a shock-expansion tube is used for combustor tests from Mach 12 to Mach 17+. This facility has recently been operated in a tunnel mode, to explore the possibility of semi-free-jet testing of complete engine modules at hypervelocity conditions. This paper presents a description of the current configurations and capabilities of the facilities of the NASA Langley Scramjet Test Complex, reviews the most recent scramjet tests in the facilities, and discusses comparative engine tests designed to gain information about ground facility effects on scramjet performance.
    Keywords: Research and Support Facilities (Air)
    Type: NASA-TM-111658 , NAS 1.15:111658 , AIAA Paper 96-3243 , AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 01, 1996; Lake Buena Vista, FL; United States|AIAA/ASME/SAE/ASEE Joint Propulsion Conference; Jul 01, 1996 - Jul 03, 1996; Lake Buena Vista, FL; United States
    Format: text
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    NASA TECHNICAL REPORTS
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