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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

RACORO Continental Boundary Layer Cloud Investigations: 1. Case Study Development and Ensemble Large-Scale Forcings

Observation-based modeling case studies of continental boundary layer clouds have been developed to study cloudy boundary layers, aerosol influences upon them, and their representation in cloud- and global-scale models. Three 60 h case study periods span the temporal evolution of cumulus, stratiform, and drizzling boundary layer cloud systems, representing mixed and transitional states rather than idealized or canonical cases. Based on in situ measurements from the Routine AAF (Atmospheric Radiation Measurement (ARM) Aerial Facility) CLOWD (Clouds with Low Optical Water Depth) Optical Radiative Observations (RACORO) field campaign and remote sensing observations, the cases are designed with a modular configuration to simplify use in large-eddy simulations (LES) and single-column models. Aircraft measurements of aerosol number size distribution are fit to lognormal functions for concise representation in models. Values of the aerosol hygroscopicity parameter, kappa, are derived from observations to be approximately 0.10, which are lower than the 0.3 typical over continents and suggestive of a large aerosol organic fraction. Ensemble large-scale forcing data sets are derived from the ARM variational analysis, European Centre for Medium-Range Weather Forecasts, and a multiscale data assimilation system. The forcings are assessed through comparison of measured bulk atmospheric and cloud properties to those computed in "trial" large-eddy simulations, where more efficient run times are enabled through modest reductions in grid resolution and domain size compared to the full-sized LES grid. Simulations capture many of the general features observed, but the state-of-the-art forcings were limited at representing details of cloud onset, and tight gradients and high-resolution transients of importance. Methods for improving the initial conditions and forcings are discussed. The cases developed are available to the general modeling community for studying continental boundary clouds.

Boundary layers↗
NASA NTRS2022

Atomic-Scale Structure and Non-Stoichiometry of Meteoritic Hibonite: A Transmission Electron Microscope Study

Hibonite (CaAl_12O_19) is a common refractory mineral in Ca-Al-rich inclusions (CAIs) in primitive meteorites. Transmission electron microscope (TEM) studies have identified enigmatic planar defects in different occurrences of hibonite in the Allende meteorite that give rise to strong streaking along c* in electron diffraction patterns. Atomic resolution high-angle annular dark-field (HAADF) imaging and energy-dispersive X-ray (EDX) analyses were used to determine the nature and origin of these planar features. HAADF images of hibonite grains reveal lamellar intergrowths of common 1.6 nm spacing, and less commonly 2.0 and 2.5 nm spacings, interspersed in stoichiometric hibonite showing 1.1 nm (002) spacing. Stoichiometric hibonite consists of alternating Ca-containing (“R”) and spinel-structured (“S”) blocks stacked in a sequence RS. In contrast, the 1.6 nm layers result from a doubled S block such that the stacking sequence is RSS, while in the widest defect observed, the stacking sequence is RSSSS. These intergrowths are epitaxial and have coherent, low-strain boundaries with the host hibonite Meteoritic hibonite shows common Ti and Mg substitution for Al in its structure. Atomic-resolution EDX maps of hibonite grains in the Allende CAI confirm the preferred site occupancy of Mg on tetragonal M3 sites in S blocks and of Ti on trigonal bipyramidal M2 and octahedral M4 sites in R blocks. Mg is highly concentrated, but Ti is absent in the planar defects where wider S blocks show Al-rich compositions compared to stoichiometric MgAl_2O_4 spinel. Therefore, Mg likely played the major role in the formation and metastability of planar defects in hibonite. Electron energy loss spectroscopy data from the Ti L_2,3 edge show the presence of mixed Ti oxidation states with ~ 15–20% of Ti as Ti^(3+) in hibonite, suggesting a direct substitution of Ti^(3+) ↔ Al^(3+) in hibonite. The remaining ~ 80–85% of Ti is present as Ti^(4+) and corresponding EDX analyses are consistent with the well-known coupled substitution 2Al^(3+) ↔ Ti^(4+) + Mg^(2+) being the major mechanism for Ti and Mg substitution in hibonite. The formation of planar defects in hibonite occurred during high-temperature nebular condensation or melting/crystallization processes. The occurrence of non-stoichiometric hibonite in the Allende CAI deviates from the mineral formation sequence predicted from equilibrium condensation models. Overall, our atomic resolution TEM observations signify non-equilibrium, kinetic-controlled crystal growth during the high-temperature formation of refractory solids in the early solar nebula.

hibonite↗
NASA NTRS1973

The use of aerial photography to quantitatively delineate mixing zones - A progress report

Aerial photography has been used to characterize and model the mixing zones which result from waste effluent discharges at seven river sites throughout the state of Wisconsin. The mixing zone is defined as the portion of the river where the waste effluent is totally mixed with the ambient receiving water. An integrated program of field sampling, mathematical modeling, laboratory modeling, and remote sensing was conducted to develop a quantitative relationship for the volumetric configuration of the mixing zone as a function of the measurable characteristics of various effluents, outfalls, and receiving water bodies. Analysis of scanning microdensitometer data extracted from 9-in. color IR transparencies has confirmed the utility of employing image density measurements to quantitatively delineate surficial concentration patterns within the mixing zone.

Lillesand, T. M.↗
NASA NTRS1985

Oscillator strengths of some Ba lines - A treatment including core-valence correlation and relativistic effects

Theoretical calculations of selected excitation energies and oscillator strengths for Ba are presented that overcome the difficulties of previous theoretical treatments. A relativistic effective-core potential treatment is used to account for the relativistic core contraction, but the outermost ten electrons are treated explicitly. Core-valence correlation can be included in this procedure in a rigorous and systematic way through a configuration-interaction calculation. Insight is gained into the importance of relativistic effects by repeating many of the calculations using an all-electron nonrelativistic treatment employing an extended Slater basis set. It is found that the intensity of the intercombination line 3P1-1S0 is accurately determined by accounting for the deviation from LS coupling through spin-orbit mixing with the 1P1 state, and that deviations from the Lande interval rule provide an accurate measure of the degree of mixing.

Bauschlicher, C. W., Jr.↗
NASA NTRS2000

PV Theories For Planetary Atmospheric Circulations

Potential vorticity (or PV) has become an important tool for the diagnosis and modeling of the Earth's atmospheric and oceanic circulations. More recently, the application of PV thinking to numerical simulations and spacecraft observations of other atmospheres, including those of Mars, Venus, and Titan, has encouraged the hope for a unified understanding of planetary circulation regimes encompassing a wide range of rotation, stratification, and forcing parameters. Specifically, the accumulated evidence suggests that zonal-mean winds and temperatures at upper tropospheric levels approximate a state of zero potential vorticity within the bounding latitudes of the westerly jets, while the poleward regions of cyclonic shear conform to a PV state that is well mixed with respect to its polar limit. This review of the prospects for conceptual planetary circulation models will explore the possibility that the zonal-mean state of an atmosphere can be calculated in terms of a simple link between the latitudinal PV and potential temperature variation at an upper baroclinic steering level.

Allison, Michael↗
NASA NTRS2017

Chapter 8: Droughts, Floods, and Wildfires

Recent droughts and associated heat waves have reached record intensity in some regions of the United States; however, by geographical scale and duration, the Dust Bowl era of the 1930s remains the benchmark drought and extreme heat event in the historical record (very high confidence). While by some measures drought has decreased over much of the continental United States in association with long-term increases in precipitation, neither the precipitation increases nor inferred drought decreases have been confidently attributed to anthropogenic forcing. The human effect on recent major U.S. droughts is complicated. Little evidence is found for a human influence on observed precipitation deficits, but much evidence is found for a human influence on surface soil moisture deficits due to increased evapotranspiration caused by higher temperatures. Future decreases in surface (top 10 cm) soil moisture from anthropogenic forcing over most of the United States are likely as the climate warms under higher scenarios. Substantial reductions in western U.S. winter and spring snowpack are projected as the climate warms. Earlier spring melt and reduced snow water equivalent have been formally attributed to human-induced warming (high confidence) and will very likely be exacerbated as the climate continues to warm (very high confidence). Under higher scenarios, and assuming no change to current water resources management, chronic, long-duration hydrological drought is increasingly possible by the end of this century. Detectable changes in some classes of flood frequency have occurred in parts of the United States and are a mix of increases and decreases. Extreme precipitation, one of the controlling factors in flood statistics, is observed to have generally increased and is projected to continue to do so across the United States in a warming atmosphere. However, formal attribution approaches have not established a significant connection of increased riverine flooding to human-induced climate change, and the timing of any emergence of a future detectable anthropogenic change in flooding is unclear. The incidence of large forest fires in the western United States and Alaska has increased since the early 1980s and is projected to further increase in those regions as the climate warms, with profound changes to certain ecosystems.

Wehner, M. F.↗
NASA NTRS1993

Barotropic simulation of large-scale mixing in the Antarctic polar vortex

Theory and observations suggest that the Antarctic polar vortex is relatively isolated from midlatitudes, although others have interpreted the observations to indicate that there is substantial mixing from the interior of the vortex into middle latitudes. The equivalent barotropic model of Salby et al. is used to study quasi-horizontal mixing by the large-scale flow in the lower stratosphere during Southern Hemisphere spring, which is when the Antarctic ozone hole appears and disappears. The model is forced by relaxation to observed climatological monthly mean zonal-mean winds and by an idealized wave 1 or 2 forcing at the lower boundary. Mixing and transport are diagnosed primarily through Lagrangian tracer trajectories. For September, October, and November basic states, there is little or no mixing in the interior of the vortex. Mixing occurs near the critical lines for the waves: in the tropics and subtropics for a stationary wave 1, and in midlatitudes on the equatorial flank of the jet for an eastward-moving wave 2. For the December basic state, the wave 2 forcing rapidly mixes the interior of the vortex. Mixing of Lagrangian tracer particles can be significant even when the waves do not `break', as evidenced by the potential vorticity field. In the model there does not appear to be any significant transport of air out of the interior of the polar vortex prior to the vortex breakdown. The principal factor that leads to the vortex breakdown and mixing of the vortex interior is the deceleration of the jet to the point where winds in the interior of the vortex are close to the phase velocity of the wavenumber 2 forcing. The tracer transport is very similar to many aspects of the behavior of the total ozone field during the spring season.

Bowman, Kenneth P.↗
NASA NTRS1988

Hafnia-rich mixed oxide ceramics of the system HfO2-ZrO2-TiO2 for heaters and heat exchangers in electrothermal thrusters: The effects of titania on selected electrical and mechanical properties of Hafnia-rich mixed oxides in the system Hafnia-Zirconia-Titania, volume 1

A study of the effects of titania on selected properties of hafnia-rich mixed oxides in the system hafnia-zirconia-titania (HZT) was made in the region 5 to 20 mol percent titania. The studied properties included electrical conductivity, thermal expansion, and fracture strength and toughness. The effects of titania on the properties were studied for the reduced state as well as the oxidized state of the sintered mixed oxides. X-ray analysis showed that the materials were not always single phase. The oxidized compositions went from being monoclinic solid solutions at low titania additions to having three phases (two monoclinic and a titanate phase) at high additions of titania. The reduced compositions showed an increasing cubic phase presence mixed with the monoclinic phase as titania was added. The electrical conductivity increased with temperature at approximately 0.1 mhos/cm at 1700 C for all compositions. The thermal expansion coefficient decreased with increasing titania as did the monoclinic to tetragonal transformation temperature. The fracture strength of the oxidized bars tended to decrease with the addition of titania owing to the presence of the second phase titania. The fracture strength of the reduced bars exhibited a minimum corresponding to a two-phase region of monoclinic and cubic phases. When the second phases were suppressed, the titania tended to increase the fracture strength slightly in both the oxidized and reduced states. The fracture toughness followed similar trends.

Staszak, Paul Russell↗
NASA NTRS2005

A Priori Analysis of Subgrid-Scale Models for Large Eddy Simulations of Supercritical Binary-Species Mixing Layers

Models for large eddy simulation (LES) are assessed on a database obtained from direct numerical simulations (DNS) of supercritical binary-species temporal mixing layers. The analysis is performed at the DNS transitional states for heptane/nitrogen, oxygen/hydrogen and oxygen/helium mixing layers. The incorporation of simplifying assumptions that are validated on the DNS database leads to a set of LES equations that requires only models for the subgrid scale (SGS) fluxes, which arise from filtering the convective terms in the DNS equations. Constant-coefficient versions of three different models for the SGS fluxes are assessed and calibrated. The Smagorinsky SGS-flux model shows poor correlations with the SGS fluxes, while the Gradient and Similarity models have high correlations, as well as good quantitative agreement with the SGS fluxes when the calibrated coefficients are used.

turbulence↗
NASA NTRS1972

Lifetime and quenching of CO /a super 3 pi/ produced by recombination of CO2 ions in a helium afterglow.

Demonstration that rapid dissociative recombination of CO2(+) in a flowing, helium afterglow is an efficient source of CO in the a super 3 pi metastable state. Ions produced by mixing CO2 with He(2 super 3 S) recombine to produce a CO metastable afterglow with a number density as great as 10 to the 9th per sq cm. Monitoring of the (a super 3 pi-X super 1 sigma) Cameron transition in CO was used to study the lifetime and quenching of CO (a super 3 pi) by CO2, N2, NO, and He. Recombination of CO2(+) also produces CO in the d super 3 delta and a' super 3 sigma states.

Wauchop, T. S.↗
NASA NTRS1981

The variability of equatorial currents

The temporal variations of upper ocean currents along the equator, specially the equatorial undercurrent are discussed. Many mechanisms were proposed as explanations of the steady state undercurrent including vertical mixing, horizontal mixing, thermohaline effects, and nonlinear effects. All of these theories succeed to some extent in simulating some of the observed features of the undercurrent. To distinguish among these ideas, the time variability of equatorial currents was considered. Observations of surface currents, currents in the thermocline, and surface winds at the equator are shown.

Cane, M. A.↗
NASA NTRS1989

The breakup of trailing-line vortices

It is now known that Batchelor's trailing-line vortex is extremely unstable to small amplitude disturbances for swirl numbers in the neighborhood of 0.83. The results of numerical calculations are presented that show the response of the vortex in this range of swirl numbers to finite amplitude, temporal, helical disturbances. Phenomena observed include: (1) ejection of axial vorticity and momentum from the core resulting in the creation of secondary, separate vortices; (2) a great intensification of core axial vorticity and a weakening of core momentum; and (3) the production of azimuthal vorticity in the form of a tightly wrapped spiral wave. The second phenomenon eventually stablizes the vortex, which then smooths and gradually returns to an axisymmetric state. The calculations are mixed spectral-finite-difference, fourth-order accurate, and have been carried out at Reynolds numbers of 1000 to 2000. Some linearized results are also discussed in an attempt to explain the process of vortex intensification.

Jacqmin, David↗
NASA NTRS1993

Galileo SSI lunar observations: Copernican craters and soils

The Galileo spacecraft completed its first Earth-Moon flyby (EMI) in December 1990 and its second flyby (EM2) in December 1992. Copernican-age craters are among the most prominent features seen in the SSI (Solid-State Imaging) multispectral images of the Moon. The interiors, rays, and continuous ejecta deposits of these youngest craters stand out as the brightest features in images of albedo and visible/1-micron color ratios (except where impact melts are abundant). Crater colors and albedos (away from impact melts) are correlated with their geologic emplacement ages as determined from counts of superposed craters; these age-color relations can be used to estimate the emplacement age (time since impact event) for many Copernican-age craters on the near and far sides of the Moon. The spectral reflectivities of lunar soils are controlled primarily by (1) soil maturity, resulting from the soil's cumulative age of exposure to the space environment; (2) steady-state horizontal and vertical mixing of fresh crystalline materials ; and (3) the mineralogy of the underlying bedrock or megaregolith. Improved understanding of items (1) and (2) above will improve our ability to interpret item (3), especially for the use of crater compositions as probes of crustal stratigraphy. We have examined the multispectral and superposed crater frequencies of large isolated craters, mostly of Eratosthenian and Copernican ages, to avoid complications due to (1) secondaries (as they affect superposed crater counts) and (2) spatially and temporally nonuniform regolith mixing from younger, large, and nearby impacts. Crater counts are available for 11 mare craters and 9 highlands craters within the region of the Moon imaged during EM1. The EM2 coverage provides multispectral data for 10 additional craters with superposed crater counts. Also, the EM2 data provide improved spatial resolution and signal-to-noise ratios over the western nearside.

Mcewen, A. S.↗
NASA NTRS1999

Fracture Mechanics of Thin, Cracked Plates Under Tension, Bending and Out-of-Plane Shear Loading

Cracks in the skin of aircraft fuselages or other shell structures can be subjected to very complex stress states, resulting in mixed-mode fracture conditions. For example, a crack running along a stringer in a pressurized fuselage will be subject to the usual in-plane tension stresses (Mode-I) along with out-of-plane tearing stresses (Mode-III like). Crack growth and initiation in this case is correlated not only with the tensile or Mode-I stress intensity factor, K(sub I), but depends on a combination of parameters and on the history of crack growth. The stresses at the tip of a crack in a plate or shell are typically described in terms of either the small deflection Kirchhoff plate theory. However, real applications involve large deflections. We show, using the von-Karman theory, that the crack tip stress field derived on the basis of the small deflection theory is still valid for large deflections. We then give examples demonstrating the exact calculation of energy release rates and stress intensity factors for cracked plates loaded to large deflections. The crack tip fields calculated using the plate theories are an approximation to the actual three dimensional fields. Using three dimensional finite element analyses we have explored the relationship between the three dimensional elasticity theory and two dimensional plate theory results. The results show that for out-of-plane shear loading the three dimensional and Kirchhoff theory results coincide at distance greater than h/2 from the crack tip, where h/2 is the plate thickness. Inside this region, the distribution of stresses through the thickness can be very different from the plate theory predictions. We have also explored how the energy release rate varies as a function of crack length to plate thickness using the different theories. This is important in the implementation of fracture prediction methods using finite element analysis. Our experiments show that under certain conditions, during fatigue crack growth, the presence of out-of-plane shear loads induces a great deal of contact and friction on the crack surfaces, dramatically reducing crack growth rate. A series of experiments and a proposed computational approach for accounting for the friction is discussed.

Zehnder, Alan T.↗
NASA NTRS2007

Productivity Analysis of Public and Private Airports: A Causal Investigation

Around the world, airports are being viewed as enterprises, rather than public services, which are expected to be managed efficiently and provide passengers with courteous customer services. Governments are, increasingly, turning to the private sectors for their efficiency in managing the operation, financing, and development, as well as providing security for airports. Operational and financial performance evaluation has become increasingly important to airport operators due to recent trends in airport privatization. Assessing performance allows the airport operators to plan for human resources and capital investment as efficiently as possible. Productivity measurements may be used as comparisons and guidelines in strategic planning, in the internal analysis of operational efficiency and effectiveness, and in assessing the competitive position of an airport in transportation industry. The primary purpose of this paper is to investigate the operational and financial efficiencies of 22 major airports in the United States and Europe. These airports are divided into three groups based on private ownership (7 British Airport Authority airports), public ownership (8 major United States airports), and a mix of private and public ownership (7 major European Union airports. The detail ownership structures of these airports are presented in Appendix A. Total factor productivity (TFP) model was utilized to measure airport performance in terms of financial and operational efficiencies and to develop a benchmarking tool to identify the areas of strength and weakness. A regression model was then employed to measure the relationship between TFP and ownership structure. Finally a Granger causality test was performed to determine whether ownership structure is a Granger cause of TFP. The results of the analysis presented in this paper demonstrate that there is not a significant relationship between airport TFP and ownership structure. Airport productivity and efficiency is, however dependent upon the level of competition, choice of the market, and regulatory control.

Vasigh, Bijan↗
NASA NTRS2019

Experimental and Numerical Analysis of Skin-Stiffener Separation Using a Seven-Point Bend Configuration

Skin-stiffener separation in stiffened composite panels consists of a complex interaction between multiple scales of progressive damage and failure mechanisms. This work used a superposed cohesive element method of modeling resistance curve effects that represents the structural interface of a unidirectional tape skin and a fabric stiffener. Finite element models using cohesive elements with input properties obtained from tape-to-fabric interface characterization tests were compared to experimental results of a stable skin-stiffener separation characterization test using a seven-point bend fixture. This fixture deformed the stiffened panel specimens into a buckled configuration which induced mixed-mode interlaminar stress states at the skin-stiffener interface. The advantage of this fixture was the potential for more stable damage initiation and delamination growth compared to a stringer-stiffened panel under axial compression. Use of the superposed cohesive elements showed promise, but the characterization of interface material properties as input to the cohesive elements remains a crucial component to be investigated to ensure accurate prediction of skin-stiffener separation.

Kosztowny, Cyrus J. R.↗
NASA NTRS2003

Update on Area Production in Mixing of Supercritical Fluids

The focus of this research is on supercritical C7H16/N2 and O2/H2 mixing layers undergoing transitions to turbulence. The C7H16/N2 system serves as a simplified model of hydrocarbon/air systems in gas-turbine and diesel engines; the O2/H2 system is representative of liquid rocket engines. One goal of this research is to identify ways of controlling area production to increase disintegration of fluids and enhance combustion in such engines. As used in this research, "area production" signifies the fractional rate of change of surface area oriented perpendicular to the mass-fraction gradient of a mixing layer. In the study, a database of transitional states obtained from direct numerical simulations of the aforementioned mixing layers was analyzed to investigate global layer characteristics, phenomena in regions of high density-gradient magnitude (HDGM), irreversible entropy production and its relationship to the HDGM regions, and mechanisms leading to area production.

Okongo, Nora↗