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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Comparison of straight and 15 degree vectored nozzles using a six component thrust stand

This project compared the forces and moments produced by straight and 15 degree vectored nozzles. Using the six component thrust stand in the engines laboratory at California Polytechnic State University, several trials were performed. This data was then reduced using first a computer program and then later an electronic spreadsheet. This reduced data was graphed and compared. As a result of these comparisons some unexpected forces were discovered. Several more tests were run including a zero thrust test and a statistical comparison were done to discover the source of these discrepancies. As a direct result several nozzle changes were made and significant revisions to the thrust stand are being made.

Carpenter, Thomas W.↗
NASA NTRS1992

Extinction and scattering in the Orion Nebula - Comparison of optical and VLA 21 centimeter studies

We have compared VLA 21 cm continuum maps of M42 with extinction-corrected H-beta images and found that much of M42 has an excess of H-beta surface brightness. This is interpreted as reflection by particles lying close to the principal ionization front. Comparison of column densities of H I near M42 and extinction (C(H-beta)) indicates an excellent area-by-area correlation, establishing that most of the extinction in M42 arises in the neutral lid that lies on the near side of the nebula. A more quantitative comparison of (C(H-beta)) and N(H I), the column density, is consistent with this conclusion and indicates a dust scattering cross section per hydrogen atom that is similar to the value for the general interstellar medium. The usual model for extinction in the Trapezium region is that it occurs very near the stars and produces an anomalous reddening curve through modification of the nature or size distribution of the particles. These new results question the basic assumptions and conclusions of that model.

O'Dell, C. R.↗
NASA NTRS1992

Comparison of Goldstone and Magellan radar data in the equatorial plains of Venus

Goldstone radar observations of the equatorial plains of Venus provide complementary information to that obtained by Magellan. Different radar scattering mechanisms dominate each system, leading to sampling of different surface properties. Comparison of image data and derived parameters indicate that: (1) relatively high dielectric constants on impact-related parabolic features are detected in Goldstone backscatter, Magellan reflectivity, and Magellan emissivity data; the dielectric effects are overwhelmed by roughness-related signatures in Magellan synthetic aperture radar (SAR) data; (2) lava flows in Navka Planitia show dielectric variations both among and within flows; higher dielectric constants on the perimeter of some flows may by due to a decrease in vesicularity; (3) some volcanic domes are relatively smooth at the wavelength scale and probably consist of low-density deposits; (4) comparisons of Magellan SAR data with rough surface scattering models and SAR data of terrestrial surfaces indicate that the roughness characteristics of the equatorial plains surfaces are comparable to modified terrestrial lava flows; and (5) scattering properties of an equatorial 'ridge belt' structure suggest highly weathered or soil-dominated surfaces.

Plaut, Jeffrey J.↗
NASA NTRS1992

Comparison of Kalman filter estimates of zenith atmospheric path delays using the global positioning system and very long baseline interferometry

Kalman filter estimates of zenith nondispersive atmospheric path delays at Westford, Massachusetts, Fort Davis, Texas, and Mojave, California, were obtained from independent analyses of data collected during January and February 1988 using the GPS and VLBI. The apparent accuracy of the path delays is inferred by examining the estimates and covariances from both sets of data. The ability of the geodetic data to resolve zenith path delay fluctuations is determined by comparing further the GPS Kalman filter estimates with corresponding wet path delays derived from water vapor radiometric data available at Mojave over two 8-hour data spans within the comparison period. GPS and VLBI zenith path delay estimates agree well within one standard deviation formal uncertainties (from 10-20 mm for GPS and 3-15 mm for VLBI) in four out of the five possible comparisons, with maximum differences of 5 and 21 mm over 8- to 12-hour data spans.

Tralli, David M.↗
NASA NTRS1993

A comparison of the Stratospheric Aerosol and Gas Experiment II tropospheric water vapor to radiosonde measurements

Results are presented of a comparison beteen observations of the upper-tropospheric water vapor data obtained from the Stratospheric Aerosol and Gas Experiment II (SAGE II) instrument and radiosonde observations for 1987 and radiosonde-based climatologies. Colocated SAGE II-radiosonde measurement pairs are compared individually and in a zonal mean sense. A straight comparison of monthly zonal means between SAGE II and radiosondes for 1987 and Global Atmospheric Statistics (1963-1973) indicates that the clear-sky SAGE II climatology is approximately half the level of clear/cloudy sky of both radiosonde climatologies. Annual zonal means calculated from the set of profile pairs again showed SAGE II to be significantly drier in many altitude bands.

Larsen, J. C.↗
NASA NTRS1992

A study of the rotor wake of a small-scale rotor model in forward flight using laser light sheet flow visualization with comparisons to analytical models

An experimental investigation was conducted in the 14 by 22 ft subsonic tunnel at NASA Langley Research Center to quantify the rotor wake behind a scale model helicopter rotor in forward flight (mu = 0.15 and 0.23) at one thrust level (C sub T = 0.0064). The rotor system used in the present test consisted of a four-bladed, fully articulated hub and utilized blades of rectangular planform with a NACA-0012 airfoil section. A laser light sheet, seeded with propylene glycol smoke, was used to visualize the flow in planes parallel and perpendicular to the freestream flow. Quantitative measurements of vortex location, vertical skew angle, and vortex particle void radius were obtained for vortices in the flow; convective velocities were obtained for blade tip vortices. Comparisons were made between the experimental results and the wake geometry generated by computational predictions. The results of these comparisons show that the interaction between wake vortex structures is an important consideration for correctly predicting the wake geometry.

Ghee, Terence A.↗
NASA NTRS1993

Comparisons between DSMC and the Navier-Stokes equations for reentry flows

A detailed comparison is made between Navier-Stokes and DSMC calculations for flows near the continuum limit to assess the accuracy of the continuum equations in this regime. Meaningful comparisons require the use of similar physical models. This necessitates the inclusion of a separate rotational energy equation and use of slip boundary conditions. Inclusion of slip boundary conditions resulted in improved agreement between surface properties. Moreover, good agreement was obtained for the various temperatures in the nonequilibrium portion of the flow field that does not contain the shock region. Departures are noted in the shock region and in regions where thermal diffusion effects are important.

Olynick, David R.↗
NASA NTRS1992

Stratospheric models and measurements - A critical comparison

Attention is given to a program to compare stratospheric models and measurements to calculate the atmospheric effects of emissions of a projected fleet of High Speed Civil Transports on the stratosphere is presented. The goals of the effort is to establish a standard set of atmospheric measurements that can be used to test the reliability of atmospheric chemistry models, develop a method for evaluating model/data comparisons, and direct the first major international stratospheric model/data comparison.

Remsberg, Ellis E.↗
NASA NTRS1936

A comparison of corrosion-resistant steel (18 percent chromium - 8 percent nickel) and aluminum alloy (24st)

In the selection of materials for aircraft application, it is not enough to make the selection on a strength-weight basis alone. A strength-weight comparison is significant but other factors must be considered, for while a material with a high ratio of strength to weight may be perfectly satisfactory for one use, it may be totally unfitted for another. It is essential, among other things, that the probable nature, magnitude, and direction of the principal stresses be given special consideration. The following analysis has therefore been made with this in mind. An attempt has been made to cover insofar as possible the major, but not all the points, that a designer would consider in the use of "18-8", as it is commonly referred to, and 24ST aluminum alloy, as applied to aircraft. 24ST was selected for this comparison as it has practically replaced 17ST for aircraft construction and it appears to have the best combination of properties of the alloys now available for this purpose. The cost of fabrication has not been considered.

Sullivan, J E↗
NASA NTRS1955

Comparison between theoretical and experimental stresses in circular semimonocoque cylinders with rectangular cutouts

Comparisons are made between a theory for calculating stresses about rectangular cutouts in circular cylinders of semimonocoque construction published in NACA-TN-3200 and previously published NACA experimental data. The comparisons include stresses in the stringers and shear stresses in the center of the shear panels in the neighborhood of the cutout. The theory takes into account the bending flexibility of the rings in the structure, and this factor is found to be important in the calculation of stresses about cutouts. In general, when the ring flexibility is considered, good agreement is exhibited between the calculated and experimental results. (author)

Mccomb, Harvey G , Jr↗
NASA NTRS1950

Comparison of outside-surface heat-transfer coefficients for cascades of turbine blades

A comparison of available results from heat-transfer investigations on cascades of turbine blades is presented using the Nusselt equation. The conventional correlation procedure is modified by defining the Reynolds number by the average of the velocities and the pressures around the blades. The correlation of the results from impulse blades was improved by using the Reynolds number defined by the average velocity and pressure. The final comparison indicated that several variables, which possibly influence heat transfer, should be investigated.

HEAT TRANSFER, CASCADES↗
NASA NTRS1954

Comparison of effectiveness of convection-, transpiration-, and film-cooling methods with air as coolant

Various parts of aircraft propulsion engines that are in contact with hot gases often require cooling. Transpiration and film cooling, new methods that supposedly utilize cooling air more effectively than conventional convection cooling, have already been proposed. This report presents material necessary for a comparison of the cooling requirements of these three methods. Correlations that are regarded by the authors as the most reliable today are employed in evaluating each of the cooling processes. Calculations for the special case in which the gas velocity is constant along the cooled wall (flat plate) are presented. The calculations reveal that a comparison of the three cooling processes can be made on quite a general basis. The superiority of transpiration cooling is clearly shown for both laminar and turbulent flow. This superiority is reduced when the effects of radiation are included; for gas-turbine blades, however, there is evidence indicating that radiation may be neglected.

Eckert, E R G↗
NASA NTRS1993

Morphometric comparison of Icelandic lava shield volcanoes versus selected Venusian edifices

Shield volcanoes are common landforms on the silicate planets of the inner Solar System, and a wide variety have recently been documented on Venus by means of Magellan observations. In this report, we emphasize our recently completed morphometric analysis of three representative Icelandic lava shields: the classic Skjaldbreidur edifice, the low-reflief Lambahraun feature, and the monogenetic Sandfellshaed shield, as the basis for comparison with representative venusian edifices (greater than 60 km in diameter). Our detailed morphometric measurements of a representative and well-studied set of Icelandic volcanoes permits us to make comparisons with our measurements of a reasonable subset of shield-like edifices on Venus on the basis of Magellan global radar altimetry. Our study has been restricted to venusian features larger than approximately 60 km in basal diameter, on the basis of the minimum intrinsic spatial resolution (8 km) of the Magellan radar altimetry data. Finally, in order to examine the implications of landform scaling from terrestrial simple and composite shields to larger venusian varieties, we have considered the morphometry of the subaerial component of Mauna Loa, a type-locality for a composite shield edifice on Earth.

Garvin, James B.↗
NASA NTRS1994

Time series comparisons of satellite and rocketsonde temperatures in 1978-1979

The Limb Infrared Monitor of the Stratosphere (LIMS) experiment on Nimbus 7 yielded temperature-versus-pressure (T(p)) profiles for each radiance scan. The present report describes time series comparisons between LIMS and rocketsonde T(p) values at rocketsonde station locations. Sample size has increased up to 665 by this new approach, leading to better statistics for a T(p) validation. The results indicate no clearly significant bias for LIMS versus Datasonde from 10 kPa at low and mid latitudes. There is a positive LIMS bias of 2 to 3 K in the upper stratosphere at high latitudes for the Northern Hemisphere in both winter and spring. LIMS is progressively colder than Datasonde from 0.4 kPa (about -3 K) to 0.1 kPa (about -9 K) at all latitudes. A similar comparison between LIMS and the more accurate falling sphere measurements reveals an equivalent mid-latitude LIMS bias at 0.4 kPa but a much smaller bias at 0.1 kPa (-4.6 K). Because the biases do not vary noticeably with season, it is concluded that they are not a function of atmospheric state. This result confirms the robustness of the LIMS temperature retrieval technique.

Remsberg, Ellis E.↗
NASA NTRS1994

Inter-comparison of Wildfire and High-resolution Interferometer Sounder (HIS) data from STORM-FEST: An investigation of wildfire spectral channel discrepancies

This simultaneous collection of HIS spectral measurements aboard the ER-2 during STORM-FEST provided a means to explore calibration problems in the infrared bands of the Wildfire instrument. Large discrepancies in brightness temperatures were noted in Wildfire bands designed to sample the 'wings' of the strong ozone absorption band centered at 9.6 microns, where the atmospheric transmittance changes rapidly with wavelength. Examination of interchannel relationships in Wildfire data and subsequent comparison to Wildfire data synthesized from the HIS measurements suggests that a wavelength shift in the channel spectral response from those determined in the laboratory may have occurred. Based on comparisons from several flights, this spectral shift has been empirically determined to be about 0.15 micron. It is speculated that this problem resulted from a slight misalignment of the spectrometer grating or other optical elements, or was a result of extreme range in temperatures experienced by the instrument throughout the course of an ER-2 flight. A consequence of this temperature fluctuation may be a change in a position of the grating in the optical path and could result in the variations in channel spectral response during flight. These findings for Wildfire may have significant bearing on future use of the MAS because of the similarities to the original Wildfire configuration.

Jedlovec, G. J.↗
NASA NTRS1994

Comparison of LASSO and GPS time transfers

The LASSO is a technique which should allow the comparison of remote atomic clocks with sub-nanosecond precision and accuracy. The first successful time transfer using LASSO has been carried out between the Observatoire de la Cote d'Azur in France and the McDonald Observatory in Texas, United States. This paper presents a preliminary comparison of LASSO time transfer with GPS common-view time transfer.

Lewandowski, W.↗
NASA NTRS1994

Comparison of radar-altimetry data over Greenland with surface topography derived from airborne laser altimetry

During the Summers of 1991, 1992, and 1993, NASA flew a scanning laser altimeter over transects of the Greenland ice sheet. Airplane location was measured precisely using differential Global Positioning System (GPS) surveying techniques. This allowed all altimetry data to be reduced to an estimate of ice surface elevations relative to the Earth ellipsoid. Repeat flights over the same areas indicate data consistency to 10 to 20 cm. Many of the aircraft flights were made along the ERS-1 'radar-altimeter footprint track' for a commissioning phase orbit. Rigorous comparison between the ERS-1 altimeter measurements and those from the laser altimeter will require analysis of individual ERS-1 altimeter waveforms, and since the information needed to do this is not yet available, results from comparison of TOPEX (Topology Ocean Experiment) Poseidon (T/P) radar altimetry data with laser data obtained at the northernmost limit of the T/P orbits are presented.

Thomas, R. H.↗
NASA NTRS1994

A Comparison of Atomic Oxygen Erosion Yields of Carbon and Selected Polymers Exposed in Ground Based Facilities and in Low Earth Orbit

A comparison of the relative erosion yields (volume of material removed per oxygen atom arriving) for FEP Teflon, polyethylene, and pyrolytic graphite with respect to Kapton HN was performed in an atomic oxygen directed beam system, in a plasma asher, and in space on the EOIM-III (Evaluation of Oxygen Interaction with Materials-III) flight experiment. This comparison was performed to determine the sensitivity of material reaction to atomic oxygen flux, atomic oxygen fluence, and vacuum ultraviolet radiation for enabling accurate estimates of durability in ground based facilities. The relative erosion yield of pyrolytic graphite was found not to be sensitive to these factors, that for FEP was sensitive slightly to fluence and possibly ions, and that for polyethylene was found to be partially VUV and flux sensitive but more sensitive to an unknown factor. Results indicate that the ability to use these facilities for material relative durability prediction is great as long as the sensitivity of particular materials to conditions such as VUV, and atomic oxygen flux and fluence are taken into account. When testing materials of a particular group such as teflon, it may be best to use a witness sample made of a similar material that has some available space data on it. This would enable one to predict an equivalent exposure in the ground based facility.

Rutledge, Sharon K.↗