SEARCH · Engineering Papers

Results for “flat”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14

All sources NASA NTRS DOE OSTI

NASA NTRS1981

On the OLP prediction of the unstable modes of the flat plate turbulent boundary layer

The Orr et al. (OLP) stability analysis is reformulated to yield profiles from hot-wire velocity covariance data in the boundary layer of a flow over a flat plate. The proper orthogonal decomposition theorem (PODT) is used to maximize the mean square of the inner product of the velocity vector with a deterministic candidate vector function in Hilbert space. The OLP formulation couples the PODT for the eddy viscosity with a global extremum principle for the disturbance kinetic energy. Derivation of the governing equations is described analytically, as are the extraction of the mean velocity profile and the eddy viscosity. Finally, techniques for characterizing the dominant mode of the velocity field are introduced and applied to three-dimensional flow over a flat plate. Good agreement is found between the predictions, using laboratory data, and the measured energy and three-dimensional structures of the dominant eddies.

Wadia, A. R.↗

NASA NTRS1984

The AXAF technology program: The optical flats tests

The results of a technology program aimed at determining the limits of surface polishing for reflecting X-ray telescopes is presented. This program is part of the major task of developing the Advanced X-ray Astrophysical Facility (AXAF). By studying the optical properties of state-of-the-art polished flat surfaces, conclusions were drawn as to the potential capability of AXAF. Surface microtopography of the flats as well as their figure are studied by X-ray, visual, and mechanical techniques. These techniques and their results are described. The employed polishing techniques are more than adequate for the specifications of the AXAF mirrors.

Williams, A. C.↗

NASA NTRS1982

Flat-plate solar array progress and plans

The emphasis of the Flat-plate Solar Array Project has been shifted from price goals and commercial development toward longer-term, higher risk, higher-potential-payoff opportunities. The revised objectives, status, and plans of the project are presented and technical progress is noted in the areas of: large-area sheet formation; silicon feedstock refinement; flat-plate module process sequence development; and engineering and environmental testing.

Callaghan, W. T.↗

NASA NTRS1984

Supersonic separated flow past a cylindrical obstacle on a flat plate

An experimental investigation of three-dimensional boundary-layer separation on a flat plate ahead of a circular cylinder at Mach 2.36 was made. Emphasis was given to the laminar flow regime and to the flow region upstream of the cylinder. The heights and diameters of the cylinders used in the study were larger than the undisturbed boundary-layer thickness at the cylinder location. Data were obtained by oil flow visualization, Schlieren observations, static pressure measurements, and laser anemometry. Oil flow visualization revealed three separation lines on the flat plate ahead of the cylinder. A postulated flowfield structure, which was suggested by this skin-friction pattern, could not be confirmed by the velocity measurements. Velocity measurements indicated an unsteady flow structure.

Ozcan, O.↗

NASA NTRS1984

An all-reflective wide-angle flat-field telescope for space

An all-reflective wide-angle flat-field telescope (WAFFT) designed and built at Goddard Space Flight Center demonstrates the markedly improved wide-angle imaging capability which can be achieved with a design based on a recently announced class of unobscured 3-mirror optical systems. Astronomy and earth observation missions in space dictate the necessity or preference for wide-angle all-reflective systems which can provide UV through IR wavelength coverage and tolerate the space environment. An initial prototype unit has been designed to meet imaging requirements suitable for monitoring the ultraviolet sky from space. The unobscured f/4, 36 mm efl system achieves a full 20 x 30 deg field of view with resolution over a flat focal surface that is well matched for use with advanced ultraviolet image array detectors. Aspects of the design and fabrication approach, which have especially important bearing on the system solution, are reviewed; and test results are compared with the analytic performance predictions. Other possible applications of the WAFFT class of imaging system are briefly discussed. The exceptional wide-angle, high quality resolution, and very wide spectral coverage of the WAFFT-type optical system could make it a very important tool for future space research.

Hallam, K. L.↗

NASA NTRS1984

Flat-plate solar array progress and plans

The results of research into the technology of flat-plate solar arrays undertaken in the Flat-Plate Solar Array Project under the sponsorship of the U.S. Department of Energy are surveyed. Topics examined include Si refinement, ribbon-sheet substrate formation, module process sequences, environmental isolation, module engineering and testing, and photovoltaic-array economics.

Callaghan, W. T.↗

NASA NTRS1985

Accurate stratospheric particle size distributions from a flat plate collection surface

Flat plate particle collections have revealed the presence of a remarkable variety of both terrestrial and extraterrestrial material in the stratosphere. It is found that the ratio of terrestrial to extraterrestrial material and the nature of the material collected may vary significantly over short time scales. These fluctuations may be related to massive injections of volcanic ash, emissions from solid fuel rockets, or variations in the micrometeoroid flux. The variations in particle number density can be of great importance to the earth's atmospheric radiation balance, and, therefore, its climate. With the objective to assess the number density of solid particles in the stratosphere, an examination has been conducted of all particles exceeding 1 micron in average diameter for a representative suite of particles obtained from a single flat plate collection surface. Attention is given to solid particle size distributions in the stratosphere, and the origin of important stratospheric particle types.

Zolensky, M. E.↗

NASA NTRS1985

Dynamic ground effects on a two-dimensional flat plate

The effect of time-variant vortex shedding is simulated by a sequence of discrete vortices convecting downstream in the wake of a two-dimensional flat plate whose lifting condition is modeled by means of the quasi-vortex lattice method. The boundary condition of this problem is specified in such a way that the tangency condition on the surface of the flat plate is satisfied; the boundary condition also takes into account the effect of airfoil motion relative to the ground. Significant lift changes are shown to occur, due to the dynamic ground effect, that are crucial in aircraft takeoff and landing transitions.

Chen, Y.-S.↗

NASA NTRS1986

Relaminarization of the boundary layer over a flat plate in shock tube experiments

The relaminarization of the boundary layer over a flat plate in the shock tube was investigated by using the partially reflected shock wave technique. The flow Mach number was approximately 0.14, which corresponds to the inleft flow Mach number for the first row of vanes in a gas turbine. The thin film platinum heat gauges were used to measure the heat transfer rate and the Stanton number was calculated from the oscilloscope voltage traces. The Reynolds number was varied by changing the operation pressure of the shock tube and the values varied from 2.3 x 10 to the 4th to 5.3 x 10 to the 5th. For a Reynolds number range of 7 x 10 to the 4th to 3.5 x 10 to the 5th, the relaminarization of the boundary layer was observed. This phenomenon is due to the decay of the turbulence level in the flow as the reflected shock wave moves upstream from the flat plate. As the Reynolds number increased, the relaminarization was delayed and the delay was related to the turbulence generated by the reflected shock wave.

Hinckel, J. N.↗

NASA NTRS1986

Climatology of gravity waves over Poker Flat, Alaska for 1983

An analysis of short-period wind fluctuations over Poker Flat, Alaska, obtained using the Poker Flat mesosphere-stratosphere-troposphere radar is presented. Results are shown for the troposphere and lower stratosphere as well as for the upper mesosphere and lower thermosphere. Contours depict various levels of wind variance (m2s-2). These results pertain only to wind fluctuation periods lying between one and six hours. These particular fluctuations are generally considered to arise primarily from atmospheric gravity waves. Insofar as this is true, the figure thus describes a general climatology of gravity waves at high latitudes.

Balsley, B. B.↗

NASA NTRS1986

Archival of Poker Flat MST radar data

The Poker Flat MST (mesosphere stratosphere troposphere) radar has operated from early 1979 to 1985. The data recorded during that time resides on some 1100 magnetic tapes. A second set containing only the derived parameters of velocity, width and signal to noise of the primary echo at each height, plus the noise spectra, occupies another 250 tapes. While processing to generate the compressed data set does correct some known errors, no attempt has been made to identify or remove spurious echoes. Because the Poker Flat data set is such a unique and valuable resource, a proposal is made to archive the data in forms more useful for analysis. The archived data set would contain only the parameters for significant echoes with contamination from airplanes, unwanted ionospheric returns, frequently aliased Doppler signals and other sources removed. The archived set should be as good or better than the example shown and may occupy only 25 to 50 tapes.

Riddle, A. C.↗

NASA NTRS1986

Heat transfer in the stagnation region of the junction of a circular cylinder perpendicular to a flat plate

The heat transfer rate in the stagnation region of the junction of a circular cylinder perpendicular to a flat plate was measured for a range of Reynolds numbers varying from 3.0 x 10 to the 4th to 7.0 x 10 to the 5th and a flow Mach number of 0.14. The measurements were performed in a shock-tube facility using a reflected shockwave technique and thin-film platinum heat gages. The heat flux was measured for both the plate and the circular cylinder. A substantial increase in the heat transfer rate in the junction region was observed. The influence of the cylinder over the flat plate extended beyond 3/4 cylinder diameter for low Reynolds numbers. For high Reynolds numbers the maximum increase in the heat transfer rate was observed to be approximately 100 percent, but for very low Reynolds numbers a maximum increase in the heat flux to the plate by a factor of 5 was observed. The variations in the heat transfer rate to the stagnation point of the cylinder was very small.

Hinckel, J. N.↗

NASA NTRS1986

On the formation of galaxies with flat rotation curves

The dynamical development of a gravitationally unstable, initially uniform, collision-free medium has been studied by means of fully self-consistent three-dimensional numerical experiments. The system is encouraged to form just one blob by means of a small density bump, and its collapse is followed until a steady state has been reached. That blob may be interpreted as a galaxy, complete with halo. The galaxies that form have flat 'rotation curves'. Particles with initial speeds in excess of the velocity (V0) in that flat rotation curve remain unaffected by the collapse; those with speeds less than V0 join the collapse and have their speeds increased to V0. A quasi-virial argument yields correct estimates for V0.

Smith, B. F.↗

NASA NTRS1987

Kinematic tests of exotic flat cosmological models

Theoretical prejudice and inflationary models of the very early universe strongly favor the flat, Einstein-de Sitter model of the universe. At present the observational data conflict with this prejudice. This conflict can be resolved by considering flat models of the universe which posses a smooth component of energy density. The kinematics of such models, where the smooth component is relativistic particles, a cosmological term, a network of light strings, or fast-moving, light strings is studied in detail. The observational tests which can be used to discriminate between these models are also discussed. These tests include the magnitude-redshift, lookback time-redshift, angular size-redshift, and comoving volume-redshift diagrams and the growth of density fluctuations.

Charlton, Jane C.↗

NASA NTRS1987

The large-scale peculiar velocity field in flat models of the universe

The inflationary universe scenario predicts a flat universe and both adiabatic and isocurvature primordial density perturbations with the Zel'dovich spectrum. The two simplest realizations, models dominated by hot or cold dark matter, seem to be in conflict with observations. Flat models with two components of mass density, where one of the components of mass density is smoothly distributed, are examined, and the large-scale peculiar velocity field for these models is computed. For the smooth component the authors consider relativistic particles, a relic cosmological term, and light strings. At present the observational situation is unsettled, but, in principle, the large-scale peculiar velocity field is a very powerful discriminator between these different models.

Vittorio, Nicola↗

NASA NTRS1987

Experimental studies on the tripping behavior of narrow T-stiffened flat plates subjected to hydrostatic pressure and underwater shock

An experimental investigation was conducted to determine the static and dynamic responses of a specific stiffened flat plate design. The air-backed rectangular flat plates of 6061-T6 aluminum with an externally machined longitudinal narrow-flanged T-stiffener and clamped boundary conditions were subjected to static loading by water hydropump pressure and shock loading from an eight pound TNT charge detonated underwater. The dynamic test plate was instrumented to measure transient strains and free field pressure. The static test plate was instrumented to measure transient strains, plate deflection, and pressure. Emphasis was placed upon forcing static and dynamic stiffener tripping, obtaining relevant strain and pressure data, and studying the associated plate-stiffener behavior.

Budweg, H. L.↗

NASA NTRS1987

A complete sample of flat-spectrum radio sources from the Parkes 2.7 GHz survey

A complete sample of about 400 flat-spectrum radio sources from the Parkes 2700 MHz catalog with fluxes of greater than 0.5 is presented. The present sample covers all right ascensions and declinations from +10 deg to -45 deg, but excludes the galactic plane. No significant difference is found in the number-magnitude or number-redshift distributions for the flat spectrum and steep-spectrum radio quasars, in agreement with previous results for stronger sources.

Savage, A.↗

NASA NTRS1988

Flat-spectrum, variable radio sources

The general behavior of flat-spectrum (compact) radio sources is examined in terms of adiabatic-jet models. Two puzzling properties - namely, (1) the broad, rather flat spectrum (over a large range of radio frequencies) and (2) the relatively slow decay of burst amplitude (with decreasing radio frequency) - are explained. Acceptable models are characterized by the following: (1) a nearly conical, adiabatic jet, with conserved magnetic flux transverse to the axis of the jet; (2) prolonged injection (for which the duration of an event exceeds the apparent transit time scale); and (3) a transparent spectral index which is not too steep. It is suggested that the acceleration mechanism in the core of compact jets may differ substantially from that far from the core, producing a flatter electron number index s = 1.4-2.6.

O'Dell, S. L.↗