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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Mapping the magnetosheath field between the magnetopause and the bow shock - Implications for magnetospheric particle leakage

An approximate picture of the volumes occupied by particles that originate in the vicinity of the magnetopause is obtained by mapping magnetosheath magnetic field lines which drape over the magnetopause through the bow shock. Subsets of these field lines that connect to potential sites of magnetic merging on the magnetopause are also traced in the event that the particle leakage occurs preferentially where normal components of the field are present across that boundary. The results of this modeling exercise suggest that energetic magnetospheric particles which are not scattered by magnetosheath magnetic fluctuations are likely to exit the magnetosheath in the region of the quasi-parallel shock.

Luhmann, J. G.↗
NASA NTRS1986

A comparison of experimental and theoretical results for leakage, pressure gradients, and rotordynamic coefficients for tapered annular gas seal

A brief review of current annular seal theory and a discussion of the predicted effect on stiffness of tapering the seal stator are presented. An outline of Nelson's analytical-computational method for determining rotordynamic coefficients for annular compressible-flow seals is included. Modifications to increase the maximum rotor speed of an existing air-seal test apparatus at Texas A&M University are described. Experimental results, including leakage, entrance-loss coefficients, pressure distributions, and normalized rotordynamic coefficients, are presented for four convergent-tapered, smooth-rotor, smooth-stator seals. A comparison of the test results shows that an inlet-to-exit clearance ratio of 1.5 to 2.0 provides the maximum direct stiffness, a clearance ratio of 2.5 provides the greatest stability, and a clearance ratio of 1.0 provides the least stability. The experimental results are compared to theoretical results from Nelson's analysis with good agreement. Test results for cross-coupled stiffness show less sensitivity of fluid prerotation than predicted.

Elrod, D. A.↗
NASA NTRS1985

Rotary transformer design with fixed magnetizing and/or leakage inductances

A design algorithm is considered for transformers that must transfer electric power across a rotating interface. Among other features, this procedure allows the designer to minimize either weight or losses for either a fixed magnetizing inductance or a fixed leakage inductance. Numerical results are included to indicate the design trade-offs between various parameters.

Stuart, T. A.↗
NASA NTRS1987

Influence of disk leakage path on labyrinth seal inlet swirl ratio

The results of numerous investigators have shown the importance of labyrinth seal inlet swirl on the calculated dynamic stiffness of labyrinth seals. These results have not included any calculation of inlet leakage swirl as a function of geometry and sealing conditions of the given seal. This paper outlines a method of calculating the inlet swirl at a given seal by introducing a radial chamber to predict the gas swirl as it goes from the stage tip down to the seal location. For a centrifugal compressor, this amounts to including the flow path from the impeller discharge, down the back of the disk or front of the cover, then into the shaft seal or eye packing, respectively. The solution includes the friction factors of both the disk and stationary wall with account for mass flow rate and calculation of radial pressure gradients by a free vortex solution. The results of various configurations are discussed and comparisons made to other published results of disk swirl.

Kirk, R. Gordon↗
NASA NTRS1985

Effects of temperature and moisture on module leakage currents

Experimental and analytical results are presented that characterize the rate dependency of leakage currents on environmental temperature and humidity level and quantify the influence of module construction features such as rear-surface films and foils, cell-frame gap spacings, and encapsulant resistivity and thickness. The relative roles of surface and bulk resistivity are illuminated together with their differing dependencies on surface moisture, bulk moisture, and temperature.

Mon, G.↗
NASA NTRS1988

Effects of switch leakages upon Nimbus-7 SMMR calibration

A calibration model for the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) is studied. This model not only removes major drawbacks of the current calibration model but also helps us understand the performance degradation of the aging instrument. The current Nimbus-7 SMMR calibration algorithm was derived without considering the interference effect between the two orthogonally polarized signals merging at a ferrite polarization selector switch. The resulting calibrated brightness temperatures, considered as a function of scan angle phi, are not symmetric around phi=0. However, neither the origin of the asymmetry nor the manner in which the two orthogonal components are mixed is fully understood. The proposed calibration model incorporates all the leakage factors associated with the ferrite switches along the signal paths. The resulting calibration equations clarify how the orthogonal components of surface brightness are coupled at radiometers. As a consequence, the origin of the asymmetry is clearly identified and explained. In addition, the feasibility of absolute calibration using in-orbit data is discussed.

Han, Daesoo↗
NASA NTRS1990

Pressure Gauges Monitor Leakage Past Seals

Method devised to measure leakage of gas past each of two sets of primary and secondary seals into common volume from which aggregate flow measured. Although method applicable only to specific combination of flow configuration and thermal conditions, it serves as example of more general approach involving use of statistical analysis to extract additional information from measurements.

Smith, Steven A.↗
NASA NTRS1991

Dual-Diaphragm Tank With Leakage-Indicating Drain

Proposed tank includes dual diaphragm with telltale drain to separate two fluids. If leak occurred in one diaphragm, other diaphragm prevents mixing of two fluids; meanwhile, leakage accumulates in drain and alerts inspector to need for repair. Conceived for bladder tanks for use in zero gravity, concept adaptable to such commercial uses as hydraulic accumulators in industrial hydraulic systems, hydraulic systems in aircraft, and water pressure tanks.

Tuthill, Wallace C., Jr.↗
NASA NTRS1988

Effects of switch leakages upon Nimbus-7 SMMR calibration

A calibration model for the Nimbus 7 Scanning Multichannel Microwave Radiometer (SMMR) is studied. This model not only removes major drawbacks of the current calibration model but also helps in the understanding of the performance degradation of the aging instrument. The current Nimbus 7 SMMR calibration algorithm was derived without considering the interference effect between the two orthogonally polarized signals merging at a ferrite polarization selector switch. The resulting calibrated brightness temperatures, considered as a function of scan angle, are not symmetric around scan angle = 0. However, neither the origin of the asymmetry nor the manner in which the two orthogonal components are mixed has been fully understood. The new calibration model proposed incorporates all the leakage factors associated with the ferrite switches along the signal paths. The resulting calibration equations clarify how the orthogonal components of surface brightness are coupled at radiometers. As a consequence, the origin of the asymmetry is clearly identified and explained. In addition, the feasibility of absolute calibration using in-orbit data is discussed.

Han, Daesoo↗
NASA NTRS1991

An assessment of the Space Station Freedom program's leakage current requirement

The Space Station Freedom Program requires leakage currents to be limited to less than human perception level, which NASA presently defines as 5 mA for dc. The origin of this value is traced, and the literature for other dc perception threshold standards is surveyed. It is shown that while many varying standards exist, very little experimental data is available to support them.

Nagy, Michael↗
NASA NTRS1991

LDEF SP-HVDE (space plasma-high voltage drainage experiment) post-flight data on spacecraft leakage current and discharge

Two identical SP-HVDE (Space Plasma-High Voltage Drainage Experiment) trays were designed and fabricated and were flown in the NASA LDEF in the LEO environment. The trays were placed with one near the leading edge and one near the trailing edge, and investigation was performed to compare the environmental interactions on the dielectric samples of the two trays. The original objective was successfully achieved by measuring the first in-flight long term average leakage current through 156 coulometers. Less than 5 percent anomalous behavior of the coulometers were found in the post flight analysis.

Yaung, J. Y.↗
NASA NTRS1991

Centrifugal acceleration modes for incompressible fluid in the leakage annulus between a shrouded pump impeller and its housing

An algorithm is developed for calculating complex eigenvalues and eigenvectors associated with the fluid resonances and is used to analyze the perturbed flow in the leakage path between a shrouded-pump impeller and its housing. The eigenvalues obtained are consistent with the forced-response curves. First- and second-natural-frequency eigensolutions are presented for mode shapes corresponding to lateral excitations, and first-natural-frequency eigensolutions are presented for mode shapes corresponding to axial excitation.

Childs, D. W.↗
NASA NTRS1991

Effects of brush seal morphology on leakage and pressure drops

Research on brush seals which was undertaken earlier by Braun et al. (1990) is continued. Particular attention is given to the effects of brush positioning, design, and morphology on sealing surfaces, fluid leakage, and associated pressure drops. It is found that both the structure and the design of the brush are important to its performance. High resistance to the flow of the brush/fence combination can result in catastrophic failure of the brush, while at lower flow resistances, the failure is more gradual.

Braun, M. J.↗
NASA NTRS1992

Space Station Freedom delta pressure leakage rate comparison test data analysis report

Results are provided of a series of tests performed to identify the relationship between gas leakage rates across a seal at various internal to external pressure ratios. The results complement and provide insight into the analysis technique used to obtain the results presented in MSFC SSF/DEV/EL91-008, 'Space Station Freedom (S.S. Freedom) Seal Flaw Study with Delta Pressure Leak Rate Comparison Test Report.'

Sorensen, E. B.↗
NASA NTRS1992

LDEF SP-HVDE (Space Plasma-High Voltage Drainage Experiment) post-flight results: Leakage current and discharge

TRW designed and fabricated two identical SP-HVDE trays which were flown in the NASA LDEF (Long Duration Exposure Facility) for 5.75 years in the LEO (low earth orbit) environment. One tray was placed near the leading edge and one near the trailing edge, and investigations were performed to compare the environmental interactions on the dielectric samples of the two trays. Each tray consisted of six assemblies with Kapton dielectric samples of varying thicknesses (i.e., 2 mils, 3 mil, and 5 mils) biased under +/- 300 V, +/- 500 V, and +/- 1000 V. The original objective was successfully achieved by measuring the first in-flight average leakage current through the samples. Less than 5 percent of the post-flight coulometers behaved anomalously. The data should be valuable to the design and evaluation of spacecraft with high voltage systems. M/D (micrometeoroid and debris) impacts over the dielectric samples were examined using a SEM (Scanning Electron Microscope) and an EDS (Energy Dispersive x-ray Spectrometer). These impact sites were sprayed by silver which were most likely caused either by the impact or a 'local ESD' (electrostatic discharge).

Yaung, J. Y.↗
NASA NTRS1992

Lip leakage flow simulation for the Gravity Probe B gas spinup

The lip leakage flow for the Gravity Probe B (GP-B) gas spinup system is investigated using a particle simulation code on the Connection Machine (PSiCM). Particle simulation is employed because the flow conditions are in the transition regime between continuum and free molecule where particle methods are of greatest use. The dominant flow is Couette in nature and the simulation is first validated through comparison to theoretical results for Couette flow in the transition regime. A GP-B type geometry is then simulated and results are presented for two conditions, those corresponding to near the inlet and near the outlet of the spinup channel. Comparison to experiment is not made because experimental data is not yet available.

Dagum, Leonardo↗
NASA NTRS1991

LEO spacecraft leakage current and discharging phenomena - TRW LDEF SP-HVDE (space plasma-high voltage drainage experiment)

Two identical SP-HVDE trays were flown in the NASA 5.75-year LDEF (Long Duration Exposure Facility), one near the leading edge and the other near the trailing edge, in the LEO (low earth orbit) environment. Each experiment tray consisted of six assemblies with each made of Kapton dielectric samples of varying thicknesses (i.e., 2 mils, 3 mils, and 5 mils) biased under +/- 300 V, +/- 500 V, and +/- 1000 V. The objectives have been successfully achieved by measuring the first post-flight long-term (i.e. roughly 8-month experiment) average leakage current through 95 percent measurable coulombmeters and surface materials.

Yaung, J. Y.↗