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At least 883 records · Page 49
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NASA NTRS2003

Unstructured LES of Reacting Multiphase Flows in Realistic Gas Turbine Combustors

As part of the Accelerated Strategic Computing Initiative (ASCI) program, an accurate and robust simulation tool is being developed to perform high-fidelity LES studies of multiphase, multiscale turbulent reacting flows in aircraft gas turbine combustor configurations using hybrid unstructured grids. In the combustor, pressurized gas from the upstream compressor is reacted with atomized liquid fuel to produce the combustion products that drive the downstream turbine. The Large Eddy Simulation (LES) approach is used to simulate the combustor because of its demonstrated superiority over RANS in predicting turbulent mixing, which is central to combustion. This paper summarizes the accomplishments of the combustor group over the past year, concentrating mainly on the two major milestones achieved this year: 1) Large scale simulation: A major rewrite and redesign of the flagship unstructured LES code has allowed the group to perform large eddy simulations of the complete combustor geometry (all 18 injectors) with over 100 million control volumes; 2) Multi-physics simulation in complex geometry: The first multi-physics simulations including fuel spray breakup, coalescence, evaporation, and combustion are now being performed in a single periodic sector (1/18th) of an actual Pratt & Whitney combustor geometry.

Ham, Frank↗
NASA NTRS2004

Foam on Tile Impact Modeling for the STS-107 Investigation

Following the breakup of the Space Shuttle Columbia during reentry a NASA/Contractor investigation team was formed to examine the probable damage inflicted on Orbiter Thermal Protection System elements by impact of External Tank insulating foam projectiles. The authors formed a working subgroup within the larger team to apply the Smooth Particle Hydrodynamics code SPHC to the damage estimation problem. Numerical models of the Orbiter's tiles and of the Tank's foam were constructed and used as inputs into the code. Material properties needed to properly model the tiles and foam were obtained from other working subgroups who performed tests on these items for this purpose. Two- and three-dimensional models of the tiles were constructed, including the glass outer layer, the main body of LI-900 insulation, the densified lower layer of LI-900, the Nomex felt mounting layer, and the Aluminum 2024 vehicle skin. A model for the BX-250 foam including porous compression, elastic rebound, and surface erosion was developed. Code results for the tile damage and foam behavior were extensively validated through comparison with Southwest Research Institute foam-on-tile impact experiments carried out in 1999. These tests involved small projectiles striking individual tiles and small tile arrays. Following code and model validation we simulated impacts of larger foam projectiles on the examples of tile systems used on the Orbiter. Results for impacts on the main landing gear door are presented in this paper, including effects of impacts at several angles, and of rapidly rotating projectiles. General results suggest that foam impacts on tiles at about 500 mph could cause appreciable damage if the impact angle is greater than about 20 degrees. Some variations of the foam properties, such as increased brittleness or increased density could increase damage in some cases. Rotation up to 17 rps failed to increase the damage for the two cases considered. This does not rule out other cases in which the rotational energy might lead to an increase in tile damage, but suggests that in most cases rotation will not be an important factor.

Stellingwerf, R. F.↗
NASA NTRS2003

Foam on Tile Impact Modeling for the Space Shuttle Program

Following the breakup of the Space Shuttle Columbia during reentry a NASA-wide investigation team was formed to examine the probable damage inflicted on Orbiter Thermal Protection System (TPS) elements by impact of External Tank insulating foam projectiles. Our team was to apply rigorous, physics-based analysis techniques to help determine parameters of interest for an experimental test program, utilize validated codes to investigate the full range of impact scenarios, and use analysis derived models to predict aero-thermal-structural responses to entry conditions. We were to operate on a non-interference basis with the j Team, and were to supply significant findings to that team and to the Orbiter Vehicle Engineering Working Group, being responsive to any solicitations for support from these entities. The authors formed a working sub-group within the larger team to apply the Smooth Particle Hydrodynamics code SPHC to the damage estimation problem. Numerical models of the LI-900 TPS tiles and of the BX-250 foam were constructed and used as inputs into the code. Material properties needed to properly model the tiles and foam were obtained from other working sub-groups who performed tests on these items for this purpose. Two- and three- dimensional models of the tiles were constructed, including the glass outer layer, the densified lower layer of LI-900 insulation, the Nomex felt Strain Isolation Pad (SIP) mounting layer, and the underlying aluminum 2024 vehicle skin. A model for the BX-250 foam including porous compression, elastic rebound, and surface erosion was developed. Code results for the tile damage and foam behavior were extensively validated through comparison with the Southwest Research Institute (SwRI) foam-on-tile impact experiments carried out in 1999. These tests involved small projectiles striking individual tiles and small tile arrays. Following code and model validation we simulated impacts of larger ET foam projectiles on the TPS tile systems used on the wings of the orbiter. Tiles used on the Wing Acreage, the Main Landing Gear Door, and the Carrier Panels near the front edge of the wing were modeled. Foam impacts shot for the CAB investigation were modeled, as well as impacts at larger angles, including rapid rotation of the projectile, and with varying foam properties. General results suggest that foam impacts on tiles at about 500 mph could cause appreciable damage if the impact angle is greater than about 20 degrees. Some variations of the foam properties, such as increased brittleness or increased density could increase damage in some cases. Rapid (17 rps) rotation failed to increase the damage for the two cases considered. This does not rule out other cases in which the rotational energy might lead to an increase in tile damage, but suggests that in most cases rotation will not be an important factor. Similar models will be applied for other impacting materials, other velocities, and other geometries as part of the Return to Flight process.

Stellingwerf, R. F.↗
NASA NTRS2004

Ice Particle Impact on Cloud Water Content Instrumentation

Determining the total amount of water contained in an icing cloud necessitates the measurement of both the liquid droplets and ice particles. One commonly accepted method for measuring cloud water content utilizes a hot wire sensing element, which is maintained at a constant temperature. In this approach, the cloud water content is equated with the power required to keep the sense element at a constant temperature. This method inherently assumes that impinging cloud particles remain on the sensing element surface long enough to be evaporated. In the case of ice particles, this assumption requires that the particles do not bounce off the surface after impact. Recent tests aimed at characterizing ice particle impact on a thermally heated wing section, have raised questions about the validity of this assumption. Ice particles were observed to bounce off the heated wing section a very high percentage of the time. This result could have implications for Total Water Content sensors which are designed to capture ice particles, and thus do not account for bouncing or breakup of ice particles. Based on these results, a test was conducted to investigate ice particle impact on the sensing elements of the following hot-wire cloud water content probes: (1) Nevzorov Total Water Content (TWC)/Liquid Water Content (LWC) probe, (2) Science Engineering Associates TWC probe, and (3) Particle Measuring Systems King probe. Close-up video imaging was used to study ice particle impact on the sensing element of each probe. The measured water content from each probe was also determined for each cloud condition. This paper will present results from this investigation and attempt to evaluate the significance of ice particle impact on hot-wire cloud water content measurements.

Emery, Edward F.↗
NASA NTRS2003

The Water-Mist Fire Suppression Experiment (Mist): Preliminary Results From The STS-107 Mission

An investigation of the effect of water mists on premixed flame propagation has been conducted onboard the Space Shuttle to take advantage of the prolonged microgravity environment to study the effect of uniformly distributed clouds of polydisperse water mists on the speed and shape of propagating propane-air premixed flames. The suspension of a quiescent and uniform water mist cloud was confirmed during the microgravity tests. Preliminary results show good agreement with trends obtained by the numerical predictions of a computational model that uses a hybrid Eulerian-Lagrangian formulation to simulate the two-phase, flame/mist interaction. Effective flame suppression is observed at progressively higher water loadings and smaller water droplet sizes. Other unusual flame behavior, such as flame front breakup and pulsating flames, is still under investigation. The promising results from the microgravity tests will be used to assess the feasibility of using water mists as fire suppressants on Earth and on spacecraft.

Abbud-Madrid, Angel↗
NASA NTRS2003

Silicon Detector System for Cross Section Measurements

In order to estimate the radiation shielding effectiveness of materials it is necessary to know cosmic ray particles are broken up as they pass though these materials. The breakup of cosmic ray particles is characterized by the nuclear fragmentation cross sections, i.e. an effective geometrical cross section assigned to each target nucleus that represents its apparent size for fragmenting the incident particle. The values of these cross sections depend on the details of nuclear physics and cannot be calculated from first principles owing to the many-body nature of the interactions. The only way to determine them is to measure them. Once a sufficient number of cross sections have been measured, the systematic nature of the interactions allows other cross-sections to be estimated. The number of cross sections that contribute to the estimation of shielding effectiveness is very large 10,000. Fortunately most make minor contributions. These can be estimated from nuclear systematics. Only those who's uncertainties make significant contributions to the error in the shielding effectiveness estimations need to be measured. In the past it has proven difficult to measure light fragment production cross sections from the interactions of heavy cosmic rays owing to the size of the detectors used. We have developed a highly pixilated silicon (Si) detector system that can individually identify these light fragments while making efficient use of costly accelerator time. This system is an outgrowth of detector technology developed under a CDDF and a Code S sponsored cosmic ray experiment.

Source record↗
NASA NTRS2004

A Summary of the Space Shuttle Columbia Tragedy and the Use of LS Dyna in the Accident Investigation and Return to Flight Efforts

On February 1, 2003, the Space Shuttle Columbia broke apart during reentry resulting in loss of 7 crewmembers and craft. For the next several months an extensive investigation of the accident ensued involving a nationwide team of experts from NASA, industry, and academia, spanning dozens of technical disciplines. The Columbia Accident Investigation Board (CAIB), a group of experts assembled to conduct an investigation independent of NASA concluded in August, 2003 that the cause of the loss of Columbia and its crew was a breach in the left wing leading edge Reinforced Carbon-Carbon (RCC) thermal protection system initiated by the impact of thermal insulating foam that had separated from the orbiters external fuel tank 81 seconds into the missions launch. During reentry, this breach allowed superheated air to penetrate behind the leading edge and erode the aluminum structure of left wing which ultimately led to the breakup of the orbiter. In order to gain a better understanding the foam impact on the orbiters RCC wing leading edge, a multi-center team of NASA and Boeing impact experts was formed to characterize the foam and RCC materials for impact analysis using LS Dyna. Dyna predictions were validated with sub-component and full scale tests. LS Dyna proved to be a valuable asset in supporting both the Columbia Accident Investigation and NASA s return to flight efforts. This paper summarizes Columbia Accident and the nearly seven month long investigation that followed. The use of LS-DYNA in this effort is highlighted. Contributions to the investigation and return to flight efforts of the multicenter team consisting of members from NASA Glenn, NASA Langley, and Boeing Philadelphia are introduced and covered in detail in papers to follow in these proceedings.

Melis, Matthew↗
NASA NTRS2003

Quantum dots as strain- and metabolism-specific microbiological labels

Biologically conjugated quantum dots (QDs) have shown great promise as multiwavelength fluorescent labels for on-chip bioassays and eukaryotic cells. However, use of these photoluminescent nanocrystals in bacteria has not previously been reported, and their large size (3 to 10 nm) makes it unclear whether they inhibit bacterial recognition of attached molecules and whether they are able to pass through bacterial cell walls. Here we describe the use of conjugated CdSe QDs for strain- and metabolism-specific microbial labeling in a wide variety of bacteria and fungi, and our analysis was geared toward using receptors for a conjugated biomolecule that are present and active on the organism's surface. While cell surface molecules, such as glycoproteins, make excellent targets for conjugated QDs, internal labeling is inconsistent and leads to large spectral shifts compared with the original fluorescence, suggesting that there is breakup or dissolution of the QDs. Transmission electron microscopy of whole mounts and thin sections confirmed that bacteria are able to extract Cd and Se from QDs in a fashion dependent upon the QD surface conjugate.

NASA Center JPL↗
NASA NTRS2002

Nuclear model calculations and their role in space radiation research

Proper assessments of spacecraft shielding requirements and concomitant estimates of risk to spacecraft crews from energetic space radiation requires accurate, quantitative methods of characterizing the compositional changes in these radiation fields as they pass through thick absorbers. These quantitative methods are also needed for characterizing accelerator beams used in space radiobiology studies. Because of the impracticality/impossibility of measuring these altered radiation fields inside critical internal body organs of biological test specimens and humans, computational methods rather than direct measurements must be used. Since composition changes in the fields arise from nuclear interaction processes (elastic, inelastic and breakup), knowledge of the appropriate cross sections and spectra must be available. Experiments alone cannot provide the necessary cross section and secondary particle (neutron and charged particle) spectral data because of the large number of nuclear species and wide range of energies involved in space radiation research. Hence, nuclear models are needed. In this paper current methods of predicting total and absorption cross sections and secondary particle (neutrons and ions) yields and spectra for space radiation protection analyses are reviewed. Model shortcomings are discussed and future needs presented. c2002 COSPAR. Published by Elsevier Science Ltd. All right reserved.

NASA Center JSC↗
NASA NTRS1998

Production of neutrons from interactions of GCR-like particles

In order to help assess the risk to astronauts due to the long-term exposure to the natural radiation environment in space, an understanding of how the primary radiation field is changed when passing through shielding and tissue materials must be obtained. One important aspect of the change in the primary radiation field after passing through shielding materials is the production of secondary particles from the breakup of the primary. Neutrons are an important component of the secondary particle field due to their relatively high biological weighting factors, and due to their relative abundance, especially behind thick shielding scenarios. Because of the complexity of the problem, the estimation of the risk from exposure to the secondary neutron field must be handled using calculational techniques. However, those calculations will need an extensive set of neutron cross section and thicktarget neutron yield data in order to make an accurate assessment of the risk. In this paper we briefly survey the existing neutron-production data sets that are applicable to the space radiation transport problem, and we point out how neutron production from protons is different than neutron production from heavy ions. We also make comparisons of one the heavy-ion data sets with Boltzmann-Uehling-Uhlenbeck (BUU) calculations.

Non-NASA Center↗
NASA NTRS1996

Overview of nuclear fragmentation models and needs

It has been known for some time that adequate assessment of spacecraft shield requirements and concomitant estimates of astronauts radiation exposures from galactic cosmic radiation requires accurate, quantitative methods for characterizing these radiation fields as they pass through thick absorbers. The main nuclear interaction processes involved are (1) nuclear elastic and inelastic collisions, and (2) nuclear breakup (fragmentation) and electromagnetic dissociation (EMD). Nuclear fragmentation and EMD are important because they alter the elemental and isotopic composition of the transported radiation fields. At present, there is no suitably accurate theory for predicting nuclear fragmentation cross sections for all collision pairs and energies of interest in space radiation protection. Typical cross-section differences between theory and experiment range from about 25 percent to a factor of two. The resulting errors in transported flux, for high linear energy transfer (LET) particles, are comparble to these cross-section errors. In this overview, theoretical models of heavy ion fragmentation currently used to generate input data bases for cosmic-ray transport and shielding codes are reviewed. Their shortcomings are discussed. Further actions needed to improve their accuracy and generality are presented.

Review↗
NASA NTRS1994

Analysis of radiation risk from alpha particle component of solar particle events

The solar particle events (SPE) will contain a primary alpha particle component, representing a possible increase in the potential risk to astronauts during an SPE over the often studied proton component. We discuss the physical interactions of alpha particles important in describing the transport of these particles through spacecraft and body shielding. Models of light ion reactions are presented and their effects on energy and linear energy transfer (LET) spectra in shielding discussed. We present predictions of particle spectra, dose, and dose equivalent in organs of interest for SPE spectra typical of those occurring in recent solar cycles. The large events of solar cycle 19 are found to have substantial increase in biological risk from alpha particles, including a large increase in secondary neutron production from alpha particle breakup.

NASA Discipline Number 45-10↗
NASA NTRS2004

Analysis of 1970-1995 Trends in Tropospheric Ozone at Northern Hemisphere Midlatitudes with the GEOS-CHEM Model

I ] The causes of trends in tropospheric ozone at Northern Hemisphere midlatitudes from 1970 to 1995 are investigated with the GEOS-CHEM model, a global three-dimensional model of the troposphere driven by assimilated meteorological observations from the Goddard Earth Observing System (GEOS). This model is used to investigate the sensitivity of tropospheric ozone with respect to (1) changes in the anthropogenic emission of nitrogen oxides and nonmethane hydrocarbons, (2) increases in methane concentrations, (3) variations in the stratospheric source of ozone, (4) changes in solar radiation resulting from stratospheric ozone depletion, and ( 5 ) increases in tropospheric temperatures. Model results indicate that local increases in NO, emissions have caused most of the increases seen in lower tropospheric ozone over Europe and Japan. Increases in methane are responsible for roughly one fifth of the anthropogenically induced increase in tropospheric ozone at northern midlatitudes. However, changes in ozone precursors do not adequately explain either the spatial differences in observed ozone trends across midlatitudes or the observed decreases in ozone over Canada throughout the troposphere. We argue that ozone depletion in the lowermost stratosphere is likely to have reduced the stratospheric source by as much as 30% from the early 1970s to the mid 1990s. Model simulations that account for such a reduction along with reported changes in anthropogenic emissions show steep declines of ozone in the upper troposphere and variable increases in the lower troposphere that are more consistent with observations. Differential temperature trends in summer between North America and Europe may account for at least some of the remaining spatial variation in tropospheric ozone trends. Increases in ultraviolet (UV) radiation due to stratospheric ozone depletion do not appear to significantly reduce tropospheric ozone, except at midlatitudes in the Southern Hemisphere following the breakup of the ozone hole.

Fusco, Andrew C.↗
NASA NTRS1999

Orthologs, paralogs and genome comparisons

During the past decade, ancient gene duplications were recognized as one of the main forces in the generation of diverse gene families and the creation of new functional capabilities. New tools developed to search data banks for homologous sequences, and an increased availability of reliable three-dimensional structural information led to the recognition that proteins with diverse functions can belong to the same superfamily. Analyses of the evolution of these superfamilies promises to provide insights into early evolution but are complicated by several important evolutionary processes. Horizontal transfer of genes can lead to a vertical spread of innovations among organisms, therefore finding a certain property in some descendants of an ancestor does not guarantee that it was present in that ancestor. Complete or partial gene conversion between duplicated genes can yield phylogenetic trees with several, apparently independent gene duplications, suggesting an often surprising parallelism in the evolution of independent lineages. Additionally, the breakup of domains within a protein and the fusion of domains into multifunctional proteins makes the delineation of superfamilies a task that remains difficult to automate.

Non-NASA Center↗
NASA NTRS2004

Characterization of Space Shuttle External Tank Thermal Protection System (TPS) Materials in Support of the Columbia Accident Investigation

NASA suffered the loss of the seven-member crew of the Space Shuttle Columbia on February 1, 2003 when the vehicle broke apart upon re-entry to the Earth's atmosphere. The final report of the Columbia Accident Investigation Board (CAIB) determined that the accident was caused by a launch ascent incident-a suitcase-sized chunk of insulating foam on the Shuttle's External Tank (ET) broke off, and moving at almost 500 mph, struck an area of the leading edge of the Shuttle s left wing. As a result, one or more of the protective Reinforced Carbon-Carbon (RCC) panels on the wing leading edge were damaged. Upon re-entry, superheated air approaching 3,000 F breached the wing damage and caused the vehicle breakup and loss of crew. The large chunk of insulating foam that broke off during the Columbia launch was determined to come from the so-called bipod ramp area where the Shuttle s orbiter (containing crew) is attached to the ET. Underneath the foam in the bipod ramp area is a layer of TPS that is a cork-filled silicone rubber composite. In March 2003, the NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama received cured samples of the foam and composite for testing from the Michoud Assembly Facility (MAF) in New Orleans, Louisiana. The MAF is where the Shuttle's ET is manufactured. The foam and composite TPS materials for the ET have been well characterized for mechanical property data at the super-cold temperatures of the liquid oxygen and hydrogen fuels used in the ET. However, modulus data on these materials is not as well characterized. The TA Instruments 2980 Dynamic Mechanical Analyzer (DMA) was used to determine the modulus of the two TPS materials over a range of -145 to 95 C in the dual cantilever bending mode. Multi-strain, fixed frequency DMA tests were followed by multi-frequency, fixed strain tests to determine the approximate bounds of linear viscoelastic behavior for the two materials. Additional information is included in the original extended abstract.

Wingard, Charles D.↗
NASA NTRS1949

Flight Investigation of 6.25-Inch-Diameter Deacon Rocket and 10-Inch-Scale Model Rocket

Flight tests were conducted at the NACA Pilotless Aircraft Research Station, Wallops Island, to determine the characteristics of the Allegany Ballistics Laboratory's 6.2inch-diameter Deacon and lO-inch-scale model solid-propellant rocket motors. The tests were performed to assist in the development of these rockets which were designed for, and urgently needed to propel supersonic research models and pilotless aircraft. The tests showed that the rocket motors functioned properly under various flight- acceleration loads over a range of pre-ignition grain temperatures. A maximum velocity of 4180 feet per second was obtained at an elapsed time of 2.9 seconds with the 6.25-inch Deacon rocket motor at a gross weight of l9O pounds. Free-flight data of drag coefficient for the Deacon configuration for a Mach number range of 1.1 to 3.6 have been obtained from flight tests of several pounds. Camera studies of the take-off and flights of the Deacon rocket shared no evidence of breakup of propellant grains. An analysis of the forces to which the Deacon rocket grain is subjected was made. The analysis shows that the grain loading is most severe near the beginning and near the end of the rocket action time. The 10-inch-scale model rocket motor is a scaled model of the l6-inch- diameter multi-perforated, cast-grain rocket motor. A maximum velocity of 1625 feet per second at a time of 1.075 seconds was obtained at a gross weight of 309 pounds.

Watson, R. S.↗
NASA NTRS2004

Accuracy of the Cloud Integrating Nephelometer

Potential error sources for measurements with the Cloud Integrating Nephelometer (CIN) are discussed and analyzed, including systematic errors of the measurement approach, flow and particle-trajectory deviations at flight velocity, ice-crystal breakup on probe surfaces, and errors in calibration and developing scaling constants. It is concluded that errors are minimal, and that the accuracy of the CIN should be close to the systematic behavior of the CIN derived in Gerber et al (2000). Absolute calibration of the CIN with a transmissometer operating co-located in a mountain-top cloud shows that the earlier scaling constant for the optical extinction coefficient obtained by other means is within 5% of the absolute calibration value, and that the CIN measurements on the Citation aircraft flights during the CRYSTAL-FACE study are accurate.

Gerber, Hermann E.↗
NASA NTRS2005

Sensor Webs: Autonomous Rapid Response to Monitor Transient Science Events

To better understand how physical phenomena, such as volcanic eruptions, evolve over time, multiple sensor observations over the duration of the event are required. Using sensor web approaches that integrate original detections by in-situ sensors and global-coverage, lower-resolution, on-orbit assets with automated rapid response observations from high resolution sensors, more observations of significant events can be made with increased temporal, spatial, and spectral resolution. This paper describes experiments using Earth Observing 1 (EO-1) along with other space and ground assets to implement progressive mission autonomy to identify, locate and image with high resolution instruments phenomena such as wildfires, volcanoes, floods and ice breakup. The software that plans, schedules and controls the various satellite assets are used to form ad hoc constellations which enable collaborative autonomous image collections triggered by transient phenomena. This software is both flight and ground based and works in concert to run all of the required assets cohesively and includes software that is model-based, artificial intelligence software.

Mandl, Dan↗