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  • Aeronautics (General)  (3)
  • Fluid Mechanics and Heat Transfer  (2)
  • Production  (1)
  • Spacecraft Design, Testing and Performance  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Ecological conditions that determine when grazing stimulates grass production (1989)
    Springer
    Oecologia 81 (1989), S. 316-322 
    Details
    ISSN: 1432-1939
    Keywords: Compensatory growth ; Grazing ; Nitrogen ; Production ; Tropics ; Rainfall
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report the results of a pot experiment that examined the effects of three ecologically important factors controlling plant growth rates in savanna grasslands: defoliation, soil nitrogen and soil water availability. The experiment was conducted in the Amboseli region in east Africa, and was designed to simulate natural conditions as far as possible, using local soils and a grass species that is heavily grazed by abundant large herbivores. Productivity by different plant components was reduced, stimulated or unchanged by defoliation, depending on specific watering and fertilization treatments. Total above-ground production was stimulated by defoliation and was maximized at moderate clipping intensities, but this was statistically significant only when plants were watered infrequently (every 8 days), and most important, periods between clipping events were extended (at least 24 days). Under these conditions, plant growth rates were limited by water availability at the time of clipping, and soil water conserved in clipped, compared to unclipped plants. Within a given fertilization treatment, whole-plant production was never stimulated by defoliation because root growth was unaffected or inhibited by clipping. However, when fertilization was coupled to defoliation, as they are in the field, whole-plant production by fertilized and moderately clipped plants exceeded production by infertilized, unclipped plants. Under this interpretation, maximum whole-plant production coincided with optimum conditions for herbivores (maximum nitrogen concentration in grass leaves) when watering was frequent, and plants were moderately defoliated. However, these conditions were not the same as those that maximized relative above-ground stimulation of growth (infrequent watering and clipping). The results indicate that above-ground grass production can be stimulated by grazing, and when that is likely to occur. However, the results emphasize that plant production responses to defoliation can vary widely, contigent upon a complex interaction of ecological factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377077
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    Paper (German National Licenses)
    Fulltext
  • 2
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    PIV and Rotational Raman-Based Temperature Measurements for CFD Validation in a Single Injector Cooling Flow (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Film cooling is used in a wide variety of engineering applications for protection of surfaces from hot or combusting gases. The design of more efficient thin film cooling geometries/configurations could be facilitated by an ability to accurately model and predict the effectiveness of current designs using computational fluid dynamics (CFD) code predictions. Hence, a benchmark set of flow field property data were obtained for use in assessing current CFD capabilities and for development of better turbulence models. Both Particle Image Velocimetry (PIV) and spontaneous rotational Raman scattering (SRS) spectroscopy were used to acquire high quality, spatially-resolved measurements of the mean velocity, turbulence intensity and also the mean temperature and normalized root mean square (rms) temperatures in a single injector cooling flow arrangement. In addition to flowfield measurements, thermocouple measurements on the plate surface enabled estimates of the film effectiveness. Raman spectra in air were obtained across a matrix of radial and axial locations downstream from a 68.07 mm square nozzle blowing heated air over a range of temperatures and Mach numbers, across a 30.48cm long plate equipped with a single injector cooling hole. In addition, both centerline streamwise 2-component PIV and cross-stream 3-component Stereo PIV data at 15 axial stations were collected in the same flows. The velocity and temperature data were then compared against Wind-US CFD code predictions for the same flow conditions. The results of this and planned follow-on studies will support NASA's development and assessment of turbulence models for heated flows.
    Keywords: Aeronautics (General)
    Type: GRC-E-DAA-TN56253 , AIAA Aviation Forum; Jun 25, 2018 - Jun 29, 2018; Atlanta, GA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Effect of Orion Post-Touchdown Parachute Release Time on Vehicle Rollover (2008)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The effects that the Orion parachutes have on the vehicle response once the vehicle lands on the ground are examined in this report. A concern with the Orion landing is that structural accelerations will cause vehicle and/or crew injuries or that the vehicle may roll over. The parachute effects are thought to have the potential of pulling the vehicle over during conditions such as higher winds or in some cases stabilizing the vehicle by preventing its motions after touchdown. A collection of representative landing conditions is used to assess the post-touchdown parachute release effect, and it was determined that, in general, there is no significant advantage or disadvantage to releasing the parachutes past the time when the vehicle touches ground. For landing conditions when there is a high horizontal wind, retaining the parachutes has a detrimental effect on vehicle rollover because the drag force on the parachutes pulls the vehicle over. Under this condition, some form of automated parachute release should be a requirement given that an attached parachute may cause the vehicle to roll over. An automated system would ensure that the release occur within 0.50 sec of touchdown (time when parachute regains tension), which is not enough time for a crew-operated manual release.
    Keywords: Spacecraft Design, Testing and Performance
    Type: NASA/TM--2008-215066 , E-16289
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    A Comparison of Three Navier-Stokes Solvers for Exhaust Nozzle Flowfields (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A comparison of the NPARC, PAB, and WIND (previously known as NASTD) Navier-Stokes solvers is made for two flow cases with turbulent mixing as the dominant flow characteristic, a two-dimensional ejector nozzle and a Mach 1.5 elliptic jet. The objective of the work is to determine if comparable predictions of nozzle flows can be obtained from different Navier-Stokes codes employed in a multiple site research program. A single computational grid was constructed for each of the two flows and used for all of the Navier-Stokes solvers. In addition, similar k-e based turbulence models were employed in each code, and boundary conditions were specified as similarly as possible across the codes. Comparisons of mass flow rates, velocity profiles, and turbulence model quantities are made between the computations and experimental data. The computational cost of obtaining converged solutions with each of the codes is also documented. Results indicate that all of the codes provided similar predictions for the two nozzle flows. Agreement of the Navier-Stokes calculations with experimental data was good for the ejector nozzle. However, for the Mach 1.5 elliptic jet, the calculations were unable to accurately capture the development of the three dimensional elliptic mixing layer.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: NASA/TM-1999-209184 , E-11693 , NAS 1.15:209184 , AIAA Paper 99-0748 , Aerospace Sciences; Jan 11, 1999 - Jan 14, 1999; Reno, NV; United States
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    NASA TECHNICAL REPORTS
  • 5
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    Implementation and Validation of the Chien k-epsilon Turbulence Model in the Wind Navier-Stokes Code (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The two equation k-epsilon turbulence model of Chien has been implemented in the WIND Navier-Stokes flow solver. Details of the numerical solution algorithm, initialization procedure, and stability enhancements are described. Results obtained with this version of the model are compared with those from the Chien k-epsilon model in the NPARC Navier-Stokes code and from the WIND SST model for three validation cases: the incompressible flow over a smooth flat plate, the incompressible flow over a backward facing step, and the shock-induced flow separation inside a transonic diffuser. The k-epsilon model results indicate that the WIND model functions very similarly to that in NPARC, though the WIND code appears to he slightly more accurate in the treatment of the near-wall region. Comparisons of the k-epsilon model results with those from the SST model were less definitive, as each model exhibited strengths and weaknesses for each particular case.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: NASA/TM-1999-209080 , NAS 1.15:209080 , E-11662 , AIAA Paper 99-0745 , Aerospace Sciences; Jan 11, 1999 - Jan 14, 1999; Reno, NV; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Wind-US Code Physical Modeling Improvements to Complement Hypersonic Testing and Evaluation (2009)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This report gives an overview of physical modeling enhancements to the Wind-US flow solver which were made to improve the capabilities for simulation of hypersonic flows and the reliability of computations to complement hypersonic testing. The improvements include advanced turbulence models, a bypass transition model, a conjugate (or closely coupled to vehicle structure) conduction-convection heat transfer capability, and an upgraded high-speed combustion solver. A Mach 5 shock-wave boundary layer interaction problem is used to investigate the benefits of k- s and k-w based explicit algebraic stress turbulence models relative to linear two-equation models. The bypass transition model is validated using data from experiments for incompressible boundary layers and a Mach 7.9 cone flow. The conjugate heat transfer method is validated for a test case involving reacting H2-O2 rocket exhaust over cooled calorimeter panels. A dual-mode scramjet configuration is investigated using both a simplified 1-step kinetics mechanism and an 8-step mechanism. Additionally, variations in the turbulent Prandtl and Schmidt numbers are considered for this scramjet configuration.
    Keywords: Aeronautics (General)
    Type: NASA/TM-2009-215615 , AIAA-2009-193 , E-16931 , 47th Aerospace Sciences Meeting; Jan 05, 2009 - Jan 08, 2009; Orlando, Fl; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Large-Eddy Simulation: Current Capabilities, Recommended Practices, and Future Research (2009)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper presents the results of an activity by the Large Eddy Simulation (LES) Working Group of the AIAA Fluid Dynamics Technical Committee to (1) address the current capabilities of LES, (2) outline recommended practices and key considerations for using LES, and (3) identify future research needs to advance the capabilities and reliability of LES for analysis of turbulent flows. To address the current capabilities and future needs, a survey comprised of eleven questions was posed to LES Working Group members to assemble a broad range of perspectives on important topics related to LES. The responses to these survey questions are summarized with the intent not to be a comprehensive dictate on LES, but rather the perspective of one group on some important issues. A list of recommended practices is also provided, which does not treat all aspects of a LES, but provides guidance on some of the key areas that should be considered.
    Keywords: Aeronautics (General)
    Type: NASA/TM-2009-215616 , AIAA-2009-948 , E-16932 , 47th Aerospace Sciences Meeting; Jan 05, 2009 - Jan 08, 2009; Orlando, FL; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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