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  • 1
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    Measurements of thermal ion energy spectra from the Giotto encounter with Comet Halley (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Ram ion measurements made by the Giotto neutral mass spectrometer show the spatial evolution of the composition and energy spectrum of coma ions. Near the nucleus the plasma is cold and has many constituents, but at distances of the order of 200,000 km the main ions are the terminal products of water dissociation, H(+) and O(+). The ion velocity distribution at the time of the Giotto encounter is highly anisotropic. Ion flow is generally away from the comet with energies increasing with distance to the order of 100 eV in the comet frame of reference. Similarities in the proton and oxygen ion energy spectra in the comet frame suggest an acceleration mechanism other than v x B pickup.
    Keywords: ASTROPHYSICS
    Type: ESA, Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 3: Posters 415-417 (SEE N87-26714 20-90); ESA, Proceedings of
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  • 2
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    On the CO and N2 abundance in Comet Halley (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The mass 28 amu/e signal observed in the neutral mode of the Giotto neutral gas mass spectrometer (NMS) is evaluated. At 1000 km from the nucleus number density n(CO)/ n(H2O) is less than or = 0.07. The production rate of CO as a parent molecule directly from the nucleus is thus less than 7% of the H2O production rate. However, CO is also produced from an extended source in the inner coma (r is less than 20,000 km) and at 20,000 km from the nucleus, for the total equivalent CO production rate 0.05 is less than or = Q(CO)/Q(H2O) is less than or = 0.15. For N2 an upper limit Q(N2)/Q(H2O) is less than or = 0.1 is derived. No parent molecule for the CO is identified in agreement with the NMS measurements. It is proposed that CO or a very short-lived parent is released in the coma from cometary dust grains, such as the CHON particles.
    Keywords: ASTROPHYSICS
    Type: ESA Proceedings of the 20th ESLAB Symposium on the Exploration of Halley's Comet. Volume 1: Plasma and Gas; p 383-386
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  • 3
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    The influence of free-stream turbulence on turbulent boundary layers with mild adverse pressure gradients (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent boundary layers is presented for the cases of zero and mild adverse pressure gradients. With free-stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free-stream, both of which act to improve the transmission of momentum from the free-stream to the boundary layers.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-177520 , NAS 1.26:177520
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  • 4
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    Effects of free-stream turbulence on diffuser performance (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An experimental evaluation of the effects of free stream turbulence on the performance of a subsonic two dimensional diffuser was made. The diffuser's static pressure recovery coefficient was increased 11.4 and 21.1 percent at total. Divergence angles of 12 and 20 degrees respectively were obtained when the value of the inlet integral free stream scale of turbulence in the flow direction was at least 7.5 times larger than the inlet boundary layer displacement thickness, and when the inlet total free stream turbulence intensity was at least 3.5 percent. It is hypothesized that a larger scale of turbulence transmits the free stream energy to the wall more effectively and when coupled with large turbulence intensities, acts to decrease the distortion and delay separation within the diffuser.
    Keywords: AERODYNAMICS
    Type: NASA-CR-163194
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  • 5
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    Effects of small-scale, high intensity inlet turbulence on flow in a two-dimensional diffuser (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The flow through a 2D experimental diffuser with channel width 2.60 cm and divergence angle (2 theta) 9 or 20 deg is investigated experimentally for inlet Reynolds number 78,300 and velocity 43.9 m/s, with and without vertical rods to generate inlet turbulence in excess of the limits defined by Hoffmann (1981) and Hoffmann and Gonzales (1983). Measurements are obtained using a thermal wall-flow-direction probe and a single hot-wire velocity probe, and the results are presented graphically. Significant increases in the pressure-recovery coefficient of the diffuser (10 percent at 9 deg and 22 percent at 20 deg) are attributed to the action of turbulence to reduce distortion and delay separation, thus creating an altered flow condition with symmetrical velocity profiles.
    Keywords: AERODYNAMICS
    Type: ASME, Transactions, Journal of Fluids Engineering (ISSN 0098-2202); 106; 121-124
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  • 6
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    Effects of free-stream turbulence on diffuser performance (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An experimental evaluation of the effects of free-stream turbulence on the performance of a subsonic two-dimensional diffuser has been made. Increases of the diffuser's static pressure recovery coefficient of 11.3 and 23.9 percent at total included divergence angles of 12 and 20 degrees respectively were obtained when the value of the inlet integral free-stream scale of turbulence in the flow direction was at least 7.2 times larger than the inlet boundary layer displacement thickness, when the inlet total free-stream turbulence intensity was at least 3.5 percent, and when the axes of upstream rods used to generate turbulence were perpendicular to the flow and parallel to the diverging walls of the diffuser. It is hypothesized that a larger scale of turbulence with the specified eddy axis orientation transmits the free-stream energy to the walls more effectively and, when coupled with large turbulence intensities, are mechanisms which act to decrease the distortion and delay separation within the diffuser.
    Keywords: AERODYNAMICS
    Type: ASME PAPER 81-FE-4
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  • 7
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    Effects of free-stream turbulence on turbulent boundary layers with mild adverse pressure gradients (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent boundary layers is presented for the cases of zero and mild adverse pressure gradients. With free-stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free-stream, both of which act to improve the transmission of momentum from the free-stream to the boundary layers.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 88-3757 , AIAA, ASME, SIAM, and APS, National Fluid Dynamics Congress; Jul 25, 1988 - Jul 28, 1988; Cincinnati, OH; United States
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  • 8
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    Flow direction measurement criteria and techniques planned for the 40- by 80-/80- x 120-foot wind tunnel integrated systems tests (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A study was performed in order to develop the criteria for the selection of flow direction indicators for use in the Integrated Systems Tests (ISTs) of the 40 by 80/80 by 120 Foot Wind Tunnel System. The problems, requirements, and limitations of flow direction measurement in the wind tunnel were investigated. The locations and types of flow direction measurements planned in the facility were discussed. A review of current methods of flow direction measurement was made and the most suitable technique for each location was chosen. A flow direction vane for each location was chosen. A flow direction vane that employs a Hall Effect Transducer was then developed and evaluated for application during the ISTs.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-176969 , NAS 1.26:176969
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  • 9
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    Influence Of Free-Stream Turbulence On Boundary Layers (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Report describes study of influence of nearly isotropic free-stream turbulence on shape factors and skin-friction coefficients of turbulent boundary layers having mild or zero adverse pressure gradients. Results show that under stronger external free-stream turbulence, improved mixing and more effective transmission of momentum from free stream to boundary layer occur when mild adverse gradient of pressure exists, relative to zero-pressure-gradient case with same values of total intensity and integral length scale of turbulence in free stream.
    Keywords: MECHANICS
    Type: ARC-12397 , NASA Tech Briefs (ISSN 0145-319X); 16; 6; P. 74
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  • 10
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    Lunar atmospheric composition results from Apollo 17 (1973)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The Apollo 17 mass spectrometer has confirmed the existence of helium, neon, argon, and possibly molecular hydrogen in the lunar atmosphere. Helium and neon concentrations are in agreement with model predictions based on the solar wind as a source and their being noncondensable gases. Ar-40 and Ar-36 both exhibit a predawn enhancement which indicates that they are condensable gases on the nightside and are re-released into the atmosphere at the sunrise terminator. Hydrogen probably exists in the lunar atmosphere in the molecular rather than atomic state, having been released from the surface in the molecular form. Total nighttime gas concentration of known species in the lunar atmosphere is 200,000 molecules/cu cm.
    Keywords: SPACE SCIENCES
    Type: Lunar Science Conference; Mar 05, 1973 - Mar 08, 1973; Houston, TX
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