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  • Other Sources  (4)
  • 2010-2014
  • 1985-1989  (4)
  • 1987  (4)
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  • 2010-2014
  • 1985-1989  (4)
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  • 1
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    Forbidden coronal iron-like emission in the Puppis A shock front - The effect of inhomogeneities (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: CCD images of the shock front at the eastern rim of Pup A, obtained in the forbidden lines of Fe X (6374 A) and Fe XIV (5303 A), are reported and compared to Einstein high-resolution-image soft X-ray data. The observed part of the remnant is complex, containing density irregularities. Optical and X-ray data are consistent in showing a nearly flat gradient of ionization temperature behind the shock. To determine conditions in the shock, scans of surface brightness across it in the optical lines were compared to surface brightnesses predicted by idealized Sedov models. It was not possible to match both the red and green line scans by a simple, single-component model, and the failure is ascribed to the presence of the density inhomogeneities. This result has important implications for the determination of SNR shock-front models by fitting X-ray data with Sedov models.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 318; 370-378
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    A new methodology for free wake analysis using curved vortex elements (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A method using curved vortex elements was developed for helicopter rotor free wake calculations. The Basic Curve Vortex Element (BCVE) is derived from the approximate Biot-Savart integration for a parabolic arc filament. When used in conjunction with a scheme to fit the elements along a vortex filament contour, this method has a significant advantage in overall accuracy and efficiency when compared to the traditional straight-line element approach. A theoretical and numerical analysis shows that free wake flows involving close interactions between filaments should utilize curved vortex elements in order to guarantee a consistent level of accuracy. The curved element method was implemented into a forward flight free wake analysis, featuring an adaptive far wake model that utilizes free wake information to extend the vortex filaments beyond the free wake regions. The curved vortex element free wake, coupled with this far wake model, exhibited rapid convergence, even in regions where the free wake and far wake turns are interlaced. Sample calculations are presented for tip vortex motion at various advance ratios for single and multiple blade rotors. Cross-flow plots reveal that the overall downstream wake flow resembles a trailing vortex pair. A preliminary assessment shows that the rotor downwash field is insensitive to element size, even for relatively large curved elements.
    Keywords: AERODYNAMICS
    Type: NASA-CR-3958 , NAS 1.26:3958 , CDI-84-6
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Feasibility of an onboard wake vortex avoidance system (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: It was determined that an onboard vortex wake detection system using existing, proven instrumentation is technically feasible. This system might be incorporated into existing onboard systems such as a wind shear detection system, and might provide the pilot with the location of a vortex wake, as well as an evasive maneuver so that the landing separations may be reduced. It is suggested that this system might be introduced into our nation's commuter aircraft fleet and major air carrier fleet and permit a reduction of current landing separation standards, thereby reducing takeoff and departure delays.
    Keywords: AIR TRANSPORTATION AND SAFETY
    Type: NASA-CR-187521 , NAS 1.26:187521 , CDI-87-02
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Forbidden coronal iron line images of Puppis A - Cloud evaporation or shocked cloud? (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Calibrated CCD images of the eastern X-ray knot in Puppis A, made in the forbidden red and green coronal Fe lines, are discussed. They show the high-temperature gas to have a rich morphology, with the scale of some features approaching the 2.6 arcsec resolution of the data. The pictures have been compared with an Einstein HRI soft X-ray image; there is close correspondence in the position and size of structures seen in the optical forbidden lines and in the X-rays. Located near the shock front a cloud of about 0.4 pc x 0.9 pc dimension shines brilliantly in the 5303 A line. To test the hypothesis that the cloud might be evaporating into the remnant interior, the 5303 A and 6374 A intensity distributions expected for a steady state, one-fluid evaporatig model have been computed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 314; 673-689
    Format: text
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    NASA TECHNICAL REPORTS
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