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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 NTRS1973

Solar neutrinos, Martian rivers, and Praesepe.

Some recent papers on solar neutrinos, Martian rivers, and Praesepe stars are reviewed. Possible causes of solar neutrino detection rates being below theoretical expectations are quoted. The widespread presence of sinuous dendritic channels on Mars is noted. The occurrence of earth-like epochs on Mars is indicated as a plausible explanation for many such channels in terms of surface liquid water flows. The roughly uniform distribution of the Praesepe stars through the main sequence width is viewed as the indication that the excursion time off the main sequence is comparable to the time between mixings.

Sagan, C.↗
NASA NTRS1994

An evaluation with the Fourier Amplitude Sensitivity Test (FAST) of which land-surface parameters are of greatest importance in atmospheric modeling

Land-surface parameterizations based on a statistical-dynamical have been suggested recently to improve the representation of the surface forcing from heterogeneous land in atmospheric models. With this approach, land-surface characteristics are prescribed by probability density functions (PDFs) rather than single 'representative' values as in 'big-leaf' parameterizations. Yet the use of many PDFs results in an increased computational burden and requires the complex problem of representing covariances between PDFs to be addressed. In this study, a sensitivity analysis of a land-surface parameterization for atmospheric modeling was performed to evaluate the surface parameters most important to the variability of surface heat fluxes. The Fourier amplitude sensitivity test (FAST) used for this analysis determines the relative contribution of individual input parameters to the variance of energy fluxes resulting from a heterogeneous surface. By simultaneously varying all parameters according to their individual probability density functions, the number of computations needed is very much reduced by this technique. This analysis demonstrates that most of the variability of surface heat fluxes may be described by the distributions of relative stomatal conductance and surface roughness. Thus, the statistical-dynamical approach may be simplified by the use of only these two probability density functions.

Collins, Dan C.↗
NASA NTRS2002

Intercontinental Bistatic Radar Test Observation of Asteroid 1998 WT24

We describe the first intercontinental planetary radar test performed in Italy observing the near Earth asteroid (NEA) 33342 (1998 WT24) in December 2001 by means of the bistatic configurations Goldstone (California, USA)-Medicina (Italy) and Evpatoria (Ukraine)-Medicina. The experiment goal was to characterize the system for realtime radar follow-up observations of NEAs and artificial orbiting debris, in the framework of a feasibility study which aims at using the Sardinia Radio Telescope, at present under construction, also as a planetary radar facility. We report the preliminary results of the radar observations carried out by the IRA-CNR (Instituto di Radioastronomia - Consiglio Nazionale delle Ricerche) and the OATo (Osservatorio Astronomico di Torino) groups, aimed at exploring the scientific potentials of a new space radar program, using the existing facilities in Italy. The planetary radar technique is uniquely capable of investigating geometry and surface properties of various solar system objects, demonstrating advantages over the optical methods in its high spatial resolution and ability to obtain three-dimensional images. A single radar detection allows to obtain extremely accurate orbital elements, improving the instantaneous positional uncertainties by orders of magnitude with respect to an optically determined orbit. Radar is a powerful means to spatially resolve NEAs by measuring the distribution of the echo power in time delay (range) and Doppler frequency (line-of-sight velocity) with extreme precision in each coordinate, as it provides detailed information about the target physical properties like size, shape, rotation, near-surface bulk density and roughness and internal density distribution. The Medicina 32m antenna had been successfully used for the first time as the receiving part of a bistatic configuration during a test experiment (September 2001) held to check the capabilities of the entire data acquisition system. This test was possible thanks to the collaboration undertaken with the Evpatoria radar station, and consisted in the observation of the ETALON-1 low orbit satellite

Righini, S.↗
DOE OSTI2019

Full-field surface roughness

The various embodiments presented herein relate to utilizing light in conjunction with an optical Fourier transform to examine and quantify roughness of a surface. The surface includes a plurality of flaked particles. The surface is illuminated with a light beam, wherein light reflected from the surface passes through an f-theta lens and is collected at a light sensitive array (LSA). The LSA comprises light sensitive pixels. For an arrangement where the flakes are conformal with the surface, a low degree of light scattering occurs at the surface. For a surface comprising tipped and/or tilted flakes, a correlating degree of scattering of the incident light beam occurs. The surface roughness is quantified based upon the distribution of angular reflections of the scattered light represented in an image formed through use of the LSA.

36 MATERIALS SCIENCE↗
NASA NTRSDate not supplied

Effect of Roughness on Transition on the BOLT-1a Geometry in Supersonic Flow

Infrared thermography measurements on an 8.8% scale BOLT-1a model were made in the NASA Langley Probe Calibration Tunnel for freestream unit Reynolds numbers from 7.7 × 10^ -6 /m to 30.7 × 10^ -6 /m, a freestream Mach number of 3.5, and nominal angle of attack of 0 degrees. The model was printed from polycarbonate and tested before and after fine-grit sanding to evaluate the effect of surface roughness on transition. Global surface roughness measurements were obtained using a 3D optical profilometer. The temperature distributions on the upper and lower experimental surfaces of the test article were simultaneously captured using two infrared cameras. Prior to testing, the facility’s freestream environment was characterized. At a freestream unit Reynolds number of approximately 17 × 10^ -6 /m, the nozzle-wall boundary layer began to transition non-uniformly, inducing transition on the model. The boundary-layer state was determined by analyzing Stanton number distributions computed from the surface temperature measurements. The present supersonic conditions that were examined on BOLT-1a were found to display both similarities and disparities in comparison to previous hypersonic experiments.

boundary layer transition↗
NASA NTRS2013

Impact of Surface Roughness and Soil Texture on Mineral Dust Emission Fluxes Modeling

Dust production models (DPM) used to estimate vertical fluxes of mineral dust aerosols over arid regions need accurate data on soil and surface properties. The Laboratoire Inter-Universitaire des Systemes Atmospheriques (LISA) data set was developed for Northern Africa, the Middle East, and East Asia. This regional data set was built through dedicated field campaigns and include, among others, the aerodynamic roughness length, the smooth roughness length of the erodible fraction of the surface, and the dry (undisturbed) soil size distribution. Recently, satellite-derived roughness length and high-resolution soil texture data sets at the global scale have emerged and provide the opportunity for the use of advanced schemes in global models. This paper analyzes the behavior of the ERS satellite-derived global roughness length and the State Soil Geographic data base-Food and Agriculture Organization of the United Nations (STATSGO-FAO) soil texture data set (based on wet techniques) using an advanced DPM in comparison to the LISA data set over Northern Africa and the Middle East. We explore the sensitivity of the drag partition scheme (a critical component of the DPM) and of the dust vertical fluxes (intensity and spatial patterns) to the roughness length and soil texture data sets. We also compare the use of the drag partition scheme to a widely used preferential source approach in global models. Idealized experiments with prescribed wind speeds show that the ERS and STATSGO-FAO data sets provide realistic spatial patterns of dust emission and friction velocity thresholds in the region. Finally, we evaluate a dust transport model for the period of March to July 2011 with observed aerosol optical depths from Aerosol Robotic Network sites. Results show that ERS and STATSGO-FAO provide realistic simulations in the region.

textures↗
DOE OSTI2019

Elemental Characterization of Neutron-Irradiated Tungsten Using the GD-OES Technique

In reactor-relevant fusion divertor conditions, tungsten (W) will be used as an armor material due to its excellent thermal properties. It will be exposed to impurities from numerous sources, including ion implantation and mixing, neutron transmutation, low-Z plasma-facing-component (PFC) redeposition and codeposition of deuterium and tritium fuel, and trapped helium bubbles. The impurity plasma material–interaction effects are a concern because they can cause gradual degradation of the material and of plasma performance due to dust formation, fuel retention, and even changes to the thermal and mechanical properties of the W armor. It is crucial to measure the amount of impurities in W, and the glow discharge–optical emission spectroscopy (GD-OES) technique is exceptionally well suited for analysis of irradiated samples. GD-OES can measure a sample’s elemental composition by sputtering the surface of the sample, ionizing the eroded material, and measuring the optical emission of the excited atoms. In order for the GD-OES technique to be applied to neutron-irradiated tungsten samples, a mounting system for miniature samples was designed. The sample mounting and centering procedure was successful in measuring the depth distribution of control W and W alloy sample elemental concentrations. These control depth spectra will be used as elemental references for postirradiated samples. The residence time of surface layers was measured, a comparison of signals from different anodes was completed, and the influence of initial surface roughness or nonuniformity was understood. The depth distribution of an arc-welded W-0.4% rhenium (Re) alloy was measured to have a stable Re signal that was distributed evenly in the W matrix. Here, the methods developed here will allow for quantification of impurities and transmutation amounts in neutron-irradiated W. GD-OES is a powerful tool but requires calibration and careful optimization of the parameters to obtain meaningful results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1961

Local Aerodynamic Heat Transfer and Boundary-Layer Transition on Roughened Sphere-Ellipsoid Bodies at Mach Number 3.0

A wind-tunnel investigation was made to determine heat-transfer distributions on three steel sphere-ellipsoid bodies with surface roughnesses of 5, 100, and 200 microinches. Tests were conducted in the Langley 9- by 6-foot thermal structures tunnel at a Mach number of 3.0, free-stream Reynolds numbers (based on model spherical diameter) of 4.25 x 10(exp 6) and 2.76 x l0(exp 6), and at a stagnation temperature of 650 F. Pressure distributions were obtained also on a fourth model. The results indicated that the combination of surface roughness and boundary-layer cooling tended to promote early transition and nullify the advantages attributable to the blunt shape of the model for reducing local temperatures. Good correlation between experimental heating rates and those calculated from laminar theory was achieved up to the start of boundary-layer transition. The correlation also was good with the values predicted by turbulent theory for surface stations downstream from the 45 deg. station.

Deveikis, William D.↗
NASA NTRS1959

Boundary-Layer Transition on Hollow Cylinders in Supersonic Free Flight as Affected by Mach Number and a Screwthread Type of Surface Roughness

The effects of Mach number and surface-roughness variation on boundary-layer transition were studied using fin-stabilized hollow-tube models in free flight. The tests were conducted over the Mach number range from 2.8 to 7 at a nominally constant unit Reynolds number of 3 million per inch, and with heat transfer to the model surface. A screwthread type of distributed two-dimensional roughness was used. Nominal thread heights varied from 100 microinches to 2100 microinches. Transition Reynolds number was found to increase with increasing Mach number at a rate depending simultaneously on Mach number and roughness height. The laminar boundary layer was found to tolerate increasing amounts of roughness as Mach number increased. For a given Mach number an optimum roughness height was found which gave a maximum laminar run greater than was obtained with a smooth surface.

James, Carlton S.↗
NASA NTRS2018

Effect of Distributed Patch of Smooth Roughness Elements on Transition in a High-Speed Boundary Layer

Surface roughness is known to have a substantial impact on the aerothermodynamic loading of hypersonic vehicles, particularly via its influence on the laminar-turbulent transition process within the boundary layer. Numerical simulations are performed to investigate the effects of a distributed region of densely packed, smooth-shaped roughness elements on the laminar boundary layer over a 7-degree half-angle, circular cone for flow conditions corresponding to a selected trajectory point from the ascent phase of the HIFiRE-1 flight experiment. For peak-to-valley roughness heights of 50 percent or less in comparison with the thickness of the unperturbed boundary layer, the computations converge to a stationary flow, suggesting that the flow is globally stable. Analysis of convective instabilities in the wake of the roughness patch indicates two dominant families of unstable disturbances, namely, a high frequency mode that corresponds to Mack mode waves modified by the wake and a lower frequency mode that corresponds to shear layer instabilities associated with the streaks in the roughness wake. Even though the peak growth rate of the later mode is more than 35 percent greater than the peak growth rates of the Mack modes, the latter modes achieve higher amplification ratios, and hence, are likely to dominate the onset of transition, which is estimated to occur slightly later than that in the unperturbed, i.e., smooth surface boundary layer. Additional computations are performed to investigate the effects of various roughness patch configurations on a Mach 3.5 flat plate boundary layer, to help guide an upcoming experiment in the Mach 3.5 Supersonic Low Disturbance Tunnel at NASA Langley Research Center. In this case, the cumulative reinforcement of basic state distortion over the length of the roughness patch is predicted to yield a significantly earlier transition than that over a smooth plate or a plate with a shorter length roughness patch.

Meelan Choudhari↗
DOE OSTI2021

Challenges of relaxed n -type GaP on Si and strategies to enable low threading dislocation density

We directly show that doping type strongly affects the threading dislocation density (TDD) of relaxed GaP on Si, with n-type GaP having a TDD of ~3.1 × 10 7 cm -2 , nearly 30× higher than both p-type and unintentionally doped GaP at ~1.1 × 10 6 cm -2 . Such a high TDD is undesirable since n-GaP on Si serves as the starting point for the growth of epitaxial III-V/Si multi-junction solar cells. After highlighting additional challenges for highly n-doped GaP on Si including increased surface roughness, anisotropic strain relaxation, and inhomogeneous TDD distributions from blocking of the dislocation glide, we go on to show that the TDD of n-GaP on Si rises by 10× as the doping concentration increases from ~5 × 10 16 to ~2 × 10 18 cm -3 . Next, we investigate the effects of additional dopant choices on the TDD, determining that electronic effects dominate over solute effects on the dislocation velocity at these concentrations. Finally, we demonstrate the respective roles of compressively strained superlattices, low-temperature initiation, and lowered n-type doping concentration on reducing the TDD for n-GaP on Si. By combining all three, we attain relaxed n-GaP on Si with a TDD of 1.54(±0.20) × 10 6 cm -2 , approaching parity with p-GaP on Si. Such high-quality n-GaP on Si will play an important role in boosting the efficiency of epitaxial III-V/Si multi-junction solar cells.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2005

Using Remote Sensing Data to Evaluate Surface Soil Properties in Alabama Ultisols

Evaluation of surface soil properties via remote sensing could facilitate soil survey mapping, erosion prediction and allocation of agrochemicals for precision management. The objective of this study was to evaluate the relationship between soil spectral signature and surface soil properties in conventionally managed row crop systems. High-resolution RS data were acquired over bare fields in the Coastal Plain, Appalachian Plateau, and Ridge and Valley provinces of Alabama using the Airborne Terrestrial Applications Sensor multispectral scanner. Soils ranged from sandy Kandiudults to fine textured Rhodudults. Surface soil samples (0-1 cm) were collected from 163 sampling points for soil organic carbon, particle size distribution, and citrate dithionite extractable iron content. Surface roughness, soil water content, and crusting were also measured during sampling. Two methods of analysis were evaluated: 1) multiple linear regression using common spectral band ratios, and 2) partial least squares regression. Our data show that thermal infrared spectra are highly, linearly related to soil organic carbon, sand and clay content. Soil organic carbon content was the most difficult to quantify in these highly weathered systems, where soil organic carbon was generally less than 1.2%. Estimates of sand and clay content were best using partial least squares regression at the Valley site, explaining 42-59% of the variability. In the Coastal Plain, sandy surfaces prone to crusting limited estimates of sand and clay content via partial least squares and regression with common band ratios. Estimates of iron oxide content were a function of mineralogy and best accomplished using specific band ratios, with regression explaining 36-65% of the variability at the Valley and Coastal Plain sites, respectively.

Sullivan, Dana G.↗
NASA NTRS1976

Interactions of satellite-speed helium atoms with satellite surfaces. 2: Energy distributions of reflected helium atoms

Energy transfer in collisions of satellite-speed (7,000 m/sec) helium atoms with a cleaned 6061-T6 satellite-type aluminum surface was investigated using the molecular-beam technique. The amount of energy transferred was determined from the measured energy of the molecular-beam and the measured spatial and energy distributions of the reflected atoms. Spatial distributions of helium atoms scattered from a 6061-T6 aluminum surface were measured. The scattering pattern exhibits a prominent backscattering, probably due to the gross surface roughness and/or the relative lattice softness of the aluminum surface. Energy distributions of reflected helium atoms from the same surface were measured for six different incidence angles. For each incidence angle, distributions were measured at approximately sixty scattering positions. At a given scattering position, the energy spectra of the reflected helium atoms and the background gas were obtained using the retarding-field energy analyzer.

Liu, S. M.↗
NASA NTRS2010

Transition Experiments on Blunt Bodies with Isolated Roughness Elements in Hypersonic Free Flight

Smooth titanium hemispheres with isolated three-dimensional (3D) surface roughness elements were flown in the NASA Ames hypersonic ballistic range through quiescent CO2 and air environments. Global surface intensity (temperature) distributions were optically measured and thermal wakes behind individual roughness elements were analyzed to define tripping effectiveness. Real-gas Navier-Stokes calculations of model flowfields, including laminar boundary layer development in these flowfields, were conducted predict key dimensionless parameters used to correlate transition on blunt bodies in hypersonic flow. For isolated roughness elements totally immersed within the laminar boundary layer, critical roughness Reynolds numbers for flights in air were found to be higher than those measured for flights in CO2, i.e., it was easier to trip the CO2 boundary layer to turbulence. Tripping effectiveness was found to be dependent on trip location within the subsonic region of the blunt body flowfield, with effective tripping being most difficult to achieve for elements positioned closest to the stagnation point. Direct comparisons of critical roughness Reynolds numbers for 3D isolated versus 3D distributed roughness elements for flights in air showed that distributed roughness patterns were significantly more effective at tripping the blunt body laminar boundary layer to turbulence.

Reda, Daniel C.↗
NASA NTRS1993

Martian surface simulations

Computer generated surfaces have been created to aid in imaging, landing and rover studies for Mars and the moon. They are also being applied to the study of cratering histories. The surfaces are generated in steps which attempt to mimic geologic episodes. Surface roughness is realized fractally, while craters and other specific features have shapes and distributions dictated by observation. Surface materials are assigned appropriate albedos, making the images more realistic. With the inclusion of correlations between crater and rock distributions, the simulations are beginning to acquire a predictive capability.

Gaskell, Robert W.↗
NASA NTRS1981

Effect of surface roughness on elastohydrodynamic line contact

A numerical solution of an elastohydrodynamic lubrication (EHL) contact between two long rough surface cylinders is obtained. A simultaneous solution of an elasticity equation and the Reynolds equation for two partially lubricated rough surfaces is used to obtain a theoretical solution of pressure distribution, elastohydrodynamic load and film thicknesses for given speeds. A theoretical solution is also found for lubricants with pressure dependent viscosity, material properties of cylinders, and surface roughness parameters. Elastic deformation is found from hydrodynamic and contact pressure using plane strain analysis, and results indicate that for a constant central film thickness, increasing the surface roughness decreases the EHL load and there is little variation in minimum film thicknesses as the surface roughness is increased.

Majumdar, B. C.↗
NASA NTRS2016

Radiative Transfer Simulations of the Two-Dimensional Ocean Glint Reflectance and Determination of the Sea Surface Roughness

An optimized discrete-ordinate radiative transfer model (DISORT3) with a pseudo-two-dimensional bidirectional reflectance distribution function (BRDF) is used to simulate and validate ocean glint reflectances at an infrared wavelength (1036 nm) by matching model results with a complete set of BRDF measurements obtained from the NASA cloud absorption radiometer (CAR) deployed on an aircraft. The surface roughness is then obtained through a retrieval algorithm and is used to extend the simulation into the visible spectral range where diffuse reflectance becomes important. In general, the simulated reflectances and surface roughness information are in good agreement with the measurements, and the diffuse reflectance in the visible, ignored in current glint algorithms, is shown to be important. The successful implementation of this new treatment of ocean glint reflectance and surface roughness in DISORT3 will help improve glint correction algorithms in current and future ocean color remote sensing applications.

glint↗