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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

The work on Comet Halley's orbit at ESOC

The predominant error source in the final navigation for the Giotto Comet fly-by of Halley's nucleus is due to uncertainties in the comet's ephemeris. Efforts are being undertaken at ESOC to improve the prediction of the comet's state at the time of the encounter. Some of the aspects involved in the problem discussed include ways to improve old observations by re-measurement or re-reduction and encouragement to observers to take fine quality astrometric observations in the future, especially at critical times. Difficulties in the mathematical modelling of the non-gravitational forces and possible offsets of the comet's center-of-light from its center-of-mass are addressed. The available estimation techniques are also examined including one based upon selecting optimum observations.

Morley, T.↗
NASA NTRS1985

The influence of jet-grid turbulence on heat transfer from the stagnation region of a cylinder in crossflow

The effect of high-intensity turbulence on heat transfer from the stagnation region of a circular cylinder in crossflow was studied. The work was motivated by the desire to be able to more fully understand and predict the heat transfer to the leading edge of a turbine airfoil. In order to achieve high levels of turbulence with a reasonable degree of isotropy and homogeneity, a jet-injection turbulence grid was used. The jet grid provided turbulence intensities of 10 to 12 percent, measured at the test cylinder location, for downstream blowing with the blowing rate adjusted to an optimal value for flow uniformity. Heat transfer augmentation above the zeroturbulence case ranged from 37 to 53 percent for the test cylinder behind the jet grid for a cylinder Reynolds number range of 48,000 to 180,000, respectively. The level of heat transfer augmentation was found to be fairly uniform with respect to circumferential distance from the stagnation line. Stagnation point heat transfer results (expressed in terms of the Frossling number) were found to be somewhat low with respect to previous studies, when compared on the basis of equal values of the parameter Tu Re(1/2), indicating an additional Reynolds number effect as observed by previous investigators. Consequently, for a specified value of Tu Re(1/2), data obtained with a relatively high turbulence intensity will have a lower value of the Frossling number.

Obrien, J. E.↗
NASA NTRS1985

On boundary layer transition in high-subsonic and transonic flow under the influence of acoustic disturbances and free-stream turbulence

The existing data base which quantifies the roles played by the Mach number, turbulence level, and acoustic noise in the flow quality of wind tunnels is reviewed. Attention is given to the effects on end (ET) and beginning (BT) transitions in flows over a 10 deg cone in transonic channels. The Re of both ET and BT flows were significantly affected by the Mach number, acoustic noise level and the noise frequency content. A unit increment in the Mach number increased the Re beyond 3,000,000, while noise below the 1 percent level in the rms pressure coefficient did not alter the transition phenomenon. More data are required on the effects of turbulence, which was a significant factor, and in the settling chamber, test section, plenum and diffuser to trace the locations and magnitudes of the acoustic sources.

Murthy, S. V.↗
NASA NTRS1985

The performance of smooth-wall drag reducing outer-layer devices in rough-wall boundary layers

The boundary layer drag on a 0.28 m x 0.91 m flat-plate was measured to evaluate the performance of smooth-wall drag reducing outer-layer devices in rough-wall boundary layers up to a chord Reynolds number, Re(c) of 17,000. The devices were a pair of thin flat ribbons placed in tandem. The wall conditions examined were smooth, transverse-groove roughnesses having cavity width/depth ratios of 0.7 (d-type) and 3 (k-type), and sandpaper roughness (k-type) of grit sizes 180, 50 and 36. The area-averaged wall-drag was reduced compared to the respective normal levels for all wall conditions. All k-type rough walls exhibited a comparable level of drag reduction (about 7 percent) which was lower than that in the smooth-wall. The d-type rough-wall exhibited a transitional behavior in that the drag reduction dropped from the smooth-wall level to that of the k-type roughnesses with increase in the flow speed. In further experiments on a 6 meter long sandpaper roughened wall and with a pair of symmetric airfoil devices in tandem at an Re(c) of 77,500, it was possible to recover the device drag penalty fully, but no net drag reduction was achieved. The apparent loss of performance of the devices in a rough-wall is explained in terms of their inability to alter the pressure component of the drag in a significant way.

Bandyopadhyay, P. R.↗
NASA NTRS1985

Exploratory flutter test in a cryogenic wind tunnel

The feasibility of flutter testing in cryogenic wind tunnels is investigated experimentally in tests on a rigid solid-metal rectangular-planform aspect-ratio-1.5 NACA 64A010 wing model with an integral flexible beam support, cantilever mounted to the wall of the 0.3-m transonic cryogenic tunnel at NASA Langley, at Mach numbers M = 0.5 and 0.8 and Reynolds numbers Re = (4.09-18.16) x 10 to the 6th. Best results are obtained when the onset of flutter (predicted by the peak-hold subcritical-response technique of Sandford et al., 1975) is approached by adjusting stagnation pressure while keeping M and the stagnation temperature constant. The data are presented in graphs and tables and discussed. It is found that Re effects on flutter cannot be separated from mass-ratio and temperature effects for a single test model and must be interpreted from analytical trends, and that the effects detected by this procedure are so small (4.0-6.5 percent) as to fall within the scatter band of the subcritical-response predictions.

Cole, S. R.↗
NASA NTRS1985

Internal stresses in wear and corrosion resistant amorphous metallic coatings of (W/0.6/Re/0.4/)76B24 and (Mo/0.6/Ru/0.4/)82B18

Hard protective coatings in the W-Re-B and Mo-Ru-B alloy systems have been deposited by magnetron sputtering onto soda-lime glass and heat-treated AISI 52100 steel substrates. X-ray diffraction has confirmed the amorphous nature of the as-deposited coatings, and their crystallization temperatures were determined by differential thermal analysis to be 1000 and 790 C for W-Re-B and Mo-Ru-B coatings, respectively. Both coatings exhibit high microhardness; Mo-Ru-B, in addition, has excellent corrosion resistance by comparison with pure Mo at high anodic potentials. Attention is given to the influence of internal stresses on the protective properties of the coatings deposited under different conditions.

Thakoor, A. P.↗
NASA NTRS1984

Overview of NASA Lewis Research Center free-piston Stirling engine activities

A generic free-piston Stirling technology project is being conducted to develop technologies generic to both space power and terrestrial heat pump applications in a cooperative, cost-shared effort. The generic technology effort includes extensive parametric testing of a 1 kW free-piston Stirling engine (RE-1000), development of a free-piston Stirling performance computer code, design and fabrication under contract of a hydraulic output modification for RE-1000 engine tests, and a 1000-hour endurance test, under contract, of a 3 kWe free-piston Stirling/alternator engine. A newly initiated space power technology feasibility demonstration effort addresses the capability of scaling a free-piston Stirling/alternator system to about 25 kWe; developing thermodynamic cycle efficiency or equal to 70 percent of Carnot at temperature ratios in the order of 1.5 to 2.0; achieving a power conversion unit specific weight of 6 kg/kWe; operating with noncontacting gas bearings; and dynamically balancing the system. Planned engine and component design and test efforts are described.

Slaby, J. G.↗
NASA NTRS1985

Overview of free-piston Stirling technology at the NASA Lewis Research Center

An overview of the National Aeronautics and Space Administration (NASA) Lewis Research Center (Lewis) free-piston Stirling engine activities is presented. These activities include: (1) a generic free-piston Stirling technology project being conducted to develop technologies synergistic to both space power and terrestrial heat pump applications in a cooperative, cost-shared effort with the Department of Energy (DOE/Oak Ridge National Laboratory (ONRL)), and (2) a free-piston Stirling space-power technology demonstration project as part of the SP-100 program being conducted in support of the Department of Defense (DOD), DOE, and NASA/Lewis. The generic technology effort includes extensive parametric testing of a 1 kw free-piston Stirling engine (RE-1000), development and validation of a free-piston Stirling performance computer code, and fabrication and initial testing of an hydraulic output modification for the RE-1000 engine. The space power technology effort, under SP-100, addresses the status of the 25 kWe Space Power Demonstrator Engine (SPDE) including early test results.

Slaby, J. G.↗
NASA NTRS1986

Low Reynold's number boundary layers in a disturbed environment

Studies of flat plate boundary layer development were made in a low speed wind tunnel at turbulence levels from 2%to 7%. Only transitional and turbulent flows were observed in the range 280 Re sub theta 700. The mean turbulent velocity profiles display law-of-the-wall behavior but have negligible wake component. The u' disturbance profiles compare well with those of other experiments, the peak value of u'/u sub tau being about 2.5. The effect of free-stream turbulence level on turbulent skin friction can be nicely correlated with those of other investigations on a plot of u sub e/u sub tau versus Re sub theta. A discussion on the u' spectra for the transitional boundary-layers is presented.

Paik, D. K.↗
NASA NTRS1986

Users Guide to the JPL Doppler Gravity Database

Local gravity accelerations and gravimetry have been determined directly from spacecraft Doppler tracking data near the Moon and various planets by the Jet Propulsion Laboratory. Researchers in many fields have an interest in planet-wide global gravimetric mapping and its applications. Many of them use their own computers in support of their studies and would benefit from being able to directly manipulate these gravity data for inclusion in their own modeling computations. Pubication of some 150 Apollo 15 subsatellite low-altitude, high-resolution, single-orbit data sets is covered. The doppler residuals with a determination of the derivative function providing line-of-sight-gravity are both listed and plotted (on microfilm), and can be ordered in computer readable forms (tape and floppy disk). The form and format of this database as well as the methods of data reduction are explained and referenced. A skeleton computer program is provided which can be modified to support re-reductions and re-formatted presentations suitable to a wide variety of research needs undertaken on mainframe or PC class microcomputers.

Muller, P. M.↗
NASA NTRS1985

Photon and radiowave emission from peeling pressure sensitive adhesives in air

During separation of an adhesive from a polymer substrate in air, intense bursts of photons ('phE', for photon emission) and long wavelength electromagnetic radiation ('RE', for radiowave emission), similar to those reported earlier by Deryagin, et al. (1978) have been observed. In this paper, careful measurements of the phE time distributions, as well as time correlations between bursts of phE and RE, are reported. These results support the view that patches of electrical charge produced by charge separation between dissimilar materials lead to microdischarges in and near the crack tip. The role of these discharges in producing sustained phE after the discharge has been extinguished is also discussed.

Donaldson, E. E.↗
NASA NTRS1985

Low Reynolds number separation bubble research at UTRC

The facilities and techniques being applied in investigations of laminar separation bubbles on low Re airfoils at the United Technologies Research Center are described. The research is focused on developing a database and predictive models for use in designing compressor, fan and turbine blades. Flow data are gathered primarily by laser Doppler velocimetry. Experimental procedures are being devised which will permit formation of a short bubble for characterizations of the velocity profiles in and around the bubble and boundary layer. Further tests are directed at defining the size and location of the bubble and the transition in the separated shear layer. The sensitivity of the bubble to alterations in the Re, pressure gradient, turbulence intensity and the turbulence scales will be examined. The effects of surface curvature and roughness on the bubble will also be studied. Details of the wind tunnel facility and the steps being taken to define conditions for reliably producing the short bubble are outlined.

Patrick, W. P.↗
NASA NTRS1985

Separation bubble behavior for a NACA 23009 airfoil

Results are reported of experiments with smoke-wire flow visualization applied to characterizing the conditions conducive to formation of a separation bubble on an airfoil in low Re flow. An airfoil was used which spanned the test channel of the wind tunnel designed for low turbulence and noise. A wire coated with mineral oil was stretched across the channel upstream of the airfoil and heated. The smoke it gave off was flash-illuminated and photographed with ASA 3000 film. Extending the airfoil over the entire section yielded photographs that gave an essentially two-dimensional perspective. Angles of attack from 0-10 deg were investigated at Re of 33,000, 66,000, 100,000 and 133,000. Sample photographs illustrate the usefulness of the technique and apparatus in the flow regimes examined, particularly when used in conjunction with pressure tap data from the airfoil surface.

Fisher, S. S.↗
NASA NTRS1985

High Marangoni number convection in a square cavity

Steady thermocapillary flows in a square cavity are computed using a finite difference procedure. Accurate numerical solutions are obtained for as high a Reynolds number as possible, in order to characterize the nature of strongly convective flows of this general class. Only the case of capillary number going to zero is considered, so that the free surface is assumed flat at the leading order. Surface deflections are computed by domain perturbation. Boundary layer formation at different values of the Prandtl number is observed at large values of the Marangoni number and Re. The numerical results are used to infer the relevant scalings of a consistent boundary layer picture of the flow, valid asymptotically as Re goes to infinity.

Zebib, A.↗
NASA NTRS1985

Canadian medical experiments on Shuttle Flight 41-G

During the 41-G mission, two payload specialist astronauts took part in six Canadian medical experiments designed to measure how the human nervous system adapts to weightlessness, and how this might contribute to space motion sickness. Similar tests conducted pre-flight provided base-line data, and post-flight experiments examined re-adaptation to the ground. No changes were detected in the vestibulo-ocular reflex during this 8-day mission. Pronounced proprioceptive illusions were experienced, especially immediately post-flight. Tactile acuity was normal in the fingers and toes, but the ability to judge limb position was degraded. Estimates of the locations of familiar targets were grossly distorted in the absence of vision. There were no differences in taste thresholds or olfaction. Despite pre-flight tests showing unusual susceptibility to motion sickness, the Canadian payload specialist turned out to be less susceptible than normal on-orbit. Re-adaptation to the normal gravity environment occurred within the first day after landing.

Watt, D. G. D.↗
NASA NTRS1985

An overview of integrated flywheel technology for aerospace application

Space missions ranging from small scientific satellites to large manned spacecraft have, for many years, utilized systems of spinning flywheels to maintain vehicle attitude. These systems have included momentum and reaction wheels as well as control moment gyros. Extension of that technology to satisfy the additional tasks associated with energy storage has also been pursued. The combining of control and energy storage features into one system has been examined by NASA for space applications and demonstrated in the laboratory. The impact of technology advances in such areas as composite material rotors, magnetic suspensions, motor/generators, and electronics have prompted a re-evaluation of the viability of the flywheel storage system concept for aerospace applications. This paper summarizes the results of this re-examination and identifies shortfalls in the various technology areas.

Keckler, C. R.↗
NASA NTRS1986

Screening and tests of materials for space applications

The outgassing properties of materials and other considerations on materials acceptance for space applications are discussed. The uses of the outgassing data for the evaluation of important performance characteristics of a space system are indicated. The deficiencies and advantages of the ASTM-E595-77 test method and materials acceptance criteria are discussed. Also discussed are the advantages for the selection of the materials and the uses of the data provided by the long-term measurements of the outgassing rates and surface re-emission of materials. The paper concludes that the results of the ASTM method with additional derived data on the material properties can be used for the initial evaluation of a space system's characteristics. Materials data on outgassing and re-emission rates at various temperatures obtained from the more expensive, long-term QCM and TGA measurements should be obtained when a detailed analysis of a system is suggested based on the various considerations discussed in the paper.

Scialdone, J. J.↗
NASA NTRS1986

The effect of a row of Helmholtz resonators on the turbulence in a boundary layer

Detailed acoustic measurements were made of the resonator's response as the free stream speed was varied from 30 mph to 155 mph. The average sound pressure level (SPL) and peak frequency response clearly show the existence of strong tuning between the boundary layer and the resonator for the Helmholtz (f sub 0) mode as well as for the first standing wave (f sub 1) mode. The narrow speed range for tuning and the gap between the strong tuning for the Helmholtz mode and the first standing wave mode is evident. The frequency at which the peak SPL response occurred at each speed is given. The peak response for the Helmholtz mode occurred at a free stream velocity of 26 m/s (at which RE sub theta = 6,560) with a resonant frequency of 570 Hz and a sound pressure level of 141 dB. The peak response for the first standing wave occurs at the maximum wind tunnel speed of 70 m/s (at which Re sub theta = 14,900) Hz with a resonant frequency of 1,890 Hz and a sound pressure level of 154 dB. At resonance the microphones do not maintain a constant SPL, but rather the latter fluctuates in a seemingly random fashion. The values presented here are time averaged rms values. Of interest was the occurrence of phase locking between adjacent resonators witha phase lag of 180 deg. This report covers the period from 5 May to 30 September on the subject project.

Panton, R. L.↗