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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 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Flow past a flat plat with a vortex/sink combination

An attempt was made to model the so called leading edge vortex which forms over the leading edge of delta wings at high angles of attack. A simplified model was considered, namely that of a two-dimensional, inviscid, incompressible steady flow around a flat plate at an angle of attack with a stationary vortex detached on top, as well as a sink to simulate the strong spanwise flow. The results appear to agree qualitatively with experiments. A comparison was also made between the lift and the drag of this model and the corresponding results for two classical solutions: (1) that of totally attached flow over the plate with the Kutta condition satisfied at the trailing edge only; and (2) the Helmholtz solution of totally separated flow over the plate.

Mourtos, N. J.↗
NASA NTRS1985

Experimental observation of transition behavior on a flat plate

In studying transition behavior a shock tube and tunnel were used to produce high temperatures, and thin-film platinum heat gauges were used to measure local heat flux as well as to detect the transition of the laminar boundary layer over a flat plate and a cone. Initial investigations were conducted in the hypersonic shock tunnel to obtain high-temperature information for the development of an ICBM nose cone. Shock Mach numbers as large as 50 with a temperature of 15,000 K after the incident wave were produced in the driven tube. Shock tubes are used to investigate the heat transfer over various surfaces to 2500 K for the development of future gas turbines.

Nagamatsu, H. T.↗
NASA NTRS1984

Flat-plate module efficiency versus cost tradeoffs

The Five Year Research Plan energy cost methodology and in depth analyses based on the extensive data that are relevant to PV systems are used to facilitate the accomplishment of the $0.15/kWh energy cost goal. An equation is given for the five year energy cost methodology. The allocation guidelines are designed to be consistent with flat solar array (FSA) milestones for module cost, module efficiency, and the programmatic goal for energy cost. They are research targets that appear to be achievable, given prior accomplishments and planned activities in the areas of low cost silicon purification, low cost sheet material, high efficiency cell processing, low cost, long life encapsulants, and automated fabrication method. Extensive sensitivity analysis work has been performed that shows that these guidelines represent an efficient way to meet the intent of the DOE program.

Aster, R. W.↗
NASA NTRS1984

Summary of progress at the Poker Flat Observatory in Alaska

A description of the status of the Poker Flat MST Radar as of early 1983 is included in the 1983 mesosphere-stratosphere-troposphere MST Workshop Proceedings. The Observatory continues to operate in a continuous data-taking mode, except for a three-week planned campaign experiment concurrent with the STATE rocket program during June 1983. Construction of the digital preprocessing system mentioned in the last status report is all but complete. This additional improvement should be operational by late summer. The possibility of steering the array also mentioned in the last status report is being investigated. A project is underway to electronically steer the one-quarter vertical section of the array. Steering will be in finite steps within about + or - 5 deg of vertical. Successful testing of this modification may lead to eventually steering the entire array in this manner. Data analysis of the data base (now more than four years in length) continues with well over one dozen extramural scientific groups participating.

Balsley, B. B.↗
NASA NTRS1984

Flat-plate solar array progress and plans

The Flat-Plate Solar Array Project (FSA), sponsored by the U.S. Department of Energy (DOE) and managed by the Jet Propulsion Laboratory (JPL), has achieved progress in a broad range of technical activities since that reported at the Fourth European Communities Conference. A particularly important analysis has been completed recently which confirms the adoption into practice by the U.S. Photovoltaic (PV Industry, of all the low-cost module technology elements proposed at the 16th Project Integration Meeting for a $2.80/Wp (1980 U.S. Dollars) design approach in the fall of 1980. This work presents along with a projection, using the same techniques, for what is believed to be a very credible ribbon-based module design for less that $0.55/Wp (1980 U.S. Dollars). Other areas to be reported upon include low-cost Si feedstock refinement; ribbon growth; process sequence development for cells; environmental isolation; engineering science investigations; and module testing progress.

Callaghan, W. T.↗
NASA NTRS1984

A radio study of the flat spectrum component in CTB 80

Polarization data obtained from high resolution radio observations of the compact, flat spectrum core of CTB 80 allow the extraction of information on the magnetic field and thermal plasma. The magnetic field direction projected onto the plane of the sky that is derived from the average rotation measure reveals a component that runs tangentially along the southern and western periphery of the radio plateau. The thermal density suggested by the depolarization rate is sufficient, if the plasma has a temperature of several million deg, to account for the X-ray emission detected by the Einstein Observatory. Attention is given to the possible nature of a small scale feature near the edge of the radio plateau, which agrees in position with the brightest radio peak.

Strom, R. G.↗
NASA NTRS1984

Heat transfer from impinging jets to a flat plate with conical and ring protuberances

An experimental investigation of heat transfer from round jets, impinging normally on a flat plate with exchangeable, heat transfer enhancing protuberances, has been carried out, and the pertinent literature surveyed, for Reynolds numbers ranging from 14,000 to 67,000, and nozzle diameters from 3.18 to 9.52 mm. The experimental data at the stagnation point indicated laminar flow, and a significant enhancement of heat transfer there, due to the introduction of the spike protuberance; the ring protuberance reduced the local heat flux somewhat. Data have also been correlated by means of dimensional analysis and compared with the conical flow theory.

Hrycak, P.↗
NASA NTRS1985

Vortex induced lift on a flat plate with a curved forward-facing flap

Free streamline solutions are obtained for two-dimensional inviscid incompressible flow past a flat plate with a forward-facing curved flap. It is shown that it is possible to shape the curved flap to make the adverse pressure gradient on top of the flap less severe than for a straight flap and thus increase the prospects of making the flow experimentally realizable.

Tanveer, S.↗
NASA NTRS1985

A summary report on the Flat-Plate Solar Array Project Workshop on Transparent Conducting Polymers

The proceedings and technical discussions of a workshop on Transparent Conducting Polymers (TCP) for solar cell applications are reported. This is in support of the Device Research Task of the Flat-Flate Solar Array Project. The workshop took place on January 11 and 12, 1985, in Santa Barbara, California. Participants included university and industry researchers. The discussions focused on the electronic and optical properties of TCP, and on experimental issues and problems that should be addressed for high-efficiency solar cell application.

Kachare, R.↗
NASA NTRS1985

Effects of velocity profile and inclination on dual-jet-induced pressures on a flat plate in a crosswind

An experimental study was conducted to determine surface pressure distributions on a flat plate with dual subsonic, circular jets exhausting from the surface into a crossflow. The jets were arranged in both side-by-side and tandem configurations and were injected at 90 deg and 60 deg angles to the plate, with jet-to-crossflow velocity ratio of 2.2 and 4. The major objective of the study was to determine the effect of a nonuniform (vs uniform) jet velocity profile, simulating the exhaust of a turbo-fan engine. Nonuniform jets with a high-velocity outer annulus and a low-velocity core induced stronger negative pressure fields than uniform jets with the same mass flow rate. However, nondimensional lift losses (lift loss/jet thrust lift) due to such nonuniform jets were lower than lift losses due to uniform jets. Changing the injection angle from 90 deg to 60 deg resulted in moderate (for tandem jets) to significant (for side-by-side jets) increases in the induced negative pressures, even though the surface area influenced by the jets tended to reduce as the angle decreased. Jets arranged in the side-by-side configuration led to significant jet-induced lift losses exceeding, in some cases, lift losses reported for single jets.

Jakubowski, A. L.↗
NASA NTRS1985

Proceedings of the Flat-Plate Solar Array Project Workshop on Crystal Gowth for High-Efficiency Silicon Solar Cells

A Workshop on Crystal Growth for High-Efficiency Silicon Solar Cells was held December 3 and 4, 1984, in San Diego, California. The Workshop offered a day and a half of technical presentations and discussions and an afternoon session that involved a panel discussion and general discussion of areas of research that are necessary to the development of materials for high-efficiency solar cells. Topics included the theoretical and experimental aspects of growing high-quality silicon crystals, the effects of growth-process-related defects on photovoltaic devices, and the suitability of various growth technologies as cost-effective processes. Fifteen invited papers were presented, with a discussion period following each presentation. The meeting was organized by the Flat-Plate Solar Array Project of the Jet Propulsion Laboratory. These Proceedings are a record of the presentations and discussions, edited for clarity and continuity.

Dumas, K. A.↗
NASA NTRS1986

Wide-angle flat field telescope

Described is an unobscured three mirror wide angle telescopic imaging system comprised of an input baffle which provides a 20 deg (Y axis) x 30 deg (X axis) field of view, a primary mirror having a convex spherical surface, a secondary mirror having a concave ellipsoidal reflecting surface, a tertiary mirror having a concave spherical reflecting surface. The mirrors comprise mirror elements which are offset segments of parent mirrors whose axes and vertices commonly lie on the system's optical axis. An iris diaphragm forming an aperture stop is located between the secondary and tertiary mirror with its center also being coincident with the optical axis and being further located at the beam waist of input light beams reflected from the primary and secondary mirror surfaces. At the system focus following the tertiary mirror is located a flat detector which may be, for example, a TV imaging tube or a photographic film. When desirable, a spectral transmission filter is placed in front of the detector in close proximity thereto.

Hallam, K. L.↗
NASA NTRS1984

Flow past a Flat Plate with a Vortex/sink Combination

An attempt was made to model the so called leading edge vortex which forms over the leading edge of delta wings at high angles of attack. A simplified model was considered, namely that of a two-dimensional, inviscid, incompressible steady flow around a flat plate at an angle of attack with a stationary vortex detached on top, as well as a sink to simulate the strong spanwise flow. The results appear to agree qualitatively with experiments. A comparison was also made between the lift and the drag of this model and the corresponding results for two classical solutions: (1) that of totally attached flow over the plate with the Kutta condition satisfied at the trailing edge only: and (2) the Helmholtz solution of totally separated flow over the plate.

Mourtos, N. J.↗
NASA NTRS1986

Incipient transition phenomena in compressible flows over a flat plate

The full three-dimensional time-dependent compressible Navier-Stokes equations are solved by a Fourier-Chebyshev method to study the stability of compressible flows over a flat plate. After the code is validated in the linear regime, it is applied to study the existence of the secondary instability mechanism in the supersonic regime.

Erlebacher, G.↗
NASA NTRS1986

Skin friction and Reynolds stress measurements for a turbulent boundary layer following manipulation using flat plates

Research has been undertaken to experimentally study the alterations in turbulent boundary-layer properties due to turbulence manipulation using thin flat plates. Plate geometry and placement within the boundary layer were selected to coincide with recent studies. Direct, local measurements of skin friction and Reynolds stresses were made within the boundary layer downstream of the manipulator devices for cases with an approach momentum thickness Reynolds number of 3700. A strong tendency for recovery of the Reynolds stresses was observed, accompanied by local skin-friction reductions of up to 15 percent. The mean velocity profile in the manipulated flow displayed the same similarity shape in the logarithmic region as a natural boundary layer, but had an enhanced wake component. The results indicate that the plate wake plays an important role in the boundary layer response to this sort of manipulation.

Westphal, R. V.↗
NASA NTRS1986

Dual rectangular jets from a flat plate in a crossflow

Wind tunnel tests were carried out in order to study the single and dual rectangular crossflow jets injected from a flat plate perpendicular to a free stream. The length-to-width ratio of the jets was 3.97, and the spacing between the center lines was 4.7 times the width of a single jet. Surface pressure distributions were obtained for jet-to-freestream velocity ratios of 2.2 and 4, respectively. The following conclusions are offered on the basis of the experimental results: (1) the downstream extension of the negative pressures is extended to the dual jets in comparison to the single jet; (2) by increasing the jet-to-freestream velocity ratio the downstream extension of negative pressures is reduced, but negative upstream pressures become larger; (3) very high peak negative pressures occur at the front side edges of the rectangular jets compared to round jets. Velocity vector plots in the flowfield of the dual jets are given.

Kavsaoglu, M.↗
NASA NTRS1986

Aerodynamic performance of an annular flat plate airfoil cascade with nonuniform inlet velocity

The demand for increased gas turbine engine efficiency with minimum weight is leading to more complex blading designs, in which viscous and three-dimensional effects are significant. As a result, design procedures based on first principle, experimentally verified, three-dimensional aerodynamic analyses are required. This paper describes a series of experiments performed in a large-scale, subsonic, annular cascade facility specifically designed to provide three-dimensional aerodynamic data suitable for code verification. In particular, the effect of inlet velocity profile on the overall three-dimensional performance of a classical flat plate airfoil cascade is investigated over a range of incidence angles including those resulting in airfoil surface flow separation. All of the data are analyzed and correlated with appropriate nonseparated flow predictions.

Buffum, D.↗
NASA NTRS1986

Simultaneous submillimeter and infrared observations of flat-spectrum radio sources

Observations are presented of 12 extragalactic nonthermal radio emission sources made at eight wavelengths between 1.25 and 1000 microns, including the important submillimeter wavelength of 350 microns. Nine of the objects were detected at 350 microns, roughly double the number of objects of this type that have previously been detected at this wavelength. The majority of the observations were made within a three-week time span. The results, combined with other studies, show that these objects generally have flat energy distributions at wavelengths longer than 1 mm that break in most cases between 350 microns and 1 mm. At wavelengths shorter than 1 mm, the energy distributions fall with a rough power-law behavior with a spectral index of about -1. For many of the objects, there is a definite break or curvature in the energy distributions at wavelengths near 2.2 microns, with the fluxes falling even more steeply into the near infrared. At the time of the observations, both OJ 287 and 3C 273 were undergoing flares. The results are generally consistent with the flares propagating out to longer wavelengths with time.

Roellig, T. L.↗