SEARCH · Engineering Papers

Results for “phenomena”

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 415 records · Page 23

All sources NASA NTRS DOE OSTI

NASA NTRS1982

Wolf-Rayet phenomena

An outline is presented of what is currently known about the properties of stars showing Wolf-Rayet (W-R) phenomena, taking into account also the directions in which future work is leading. W-R spectra are found to be primarily an emission line spectrum superimposed on a 'hot' continuous spectrum. P Cygni absorption components are observed for some lines in some stars. A fact not realized when Thomas (1968) discussed W-R spectra is that a very few W-R stars have intrinsic absorption lines. On the basis of the spectroscopic observations, it could now be inferred that an optically thick stellar wind is involved. Many of the WN subtypes do contain some carbon. The WC subtypes contain little or no nitrogen. Attention is given to absolute visual magnitudes of W-R stars, the heterogeneity of W-R spectra, transition W-R spectra, mass loss rates, very luminous W-R objects, theoretical aspects of stellar structure and stellar winds, and evolutionary scenarios.

Conti, P. S.↗

NASA NTRS1982

Unsteady flow phenomena in industrial centrifugal compressor stage

The results of an experimental investigation on a typical centrifugal compressor stage running on an atmospheric pressure test rig are shown. Unsteady flow was invariably observed at low flow well before surge. In order to determine the influence of the statoric components, the same impeller was repeatedly tested with the same vaneless diffuser, but varying return channel geometry. Experimental results show the strong effect exerted by the return channel, both on onset and on the behavior of unsteady flow. Observed phenomena have been found to confirm well the observed dynamic behavior of full load tested machines when gas density is high enough to cause appreciable mechanical vibrations. Therefore, testing of single stages at atmospheric pressure may provide a fairly accurate prediction of this kind of aerodynamic excitation.

Bonciani, L.↗

NASA NTRS1982

Investigation of mesoscale meteorological phenomena as observed by geostationary satellite

Satellite imagery plus conventional synoptic observations were used to examine three mesoscale systems recently observed by the GOES-EAST satellite. The three systems are an arc cloud complex (ACC), mountain lee wave clouds and cloud streets parallel to the wind shear. Possible gravity-wave activity is apparent in all three cases. Of particular interest is the ACC because of its ability to interact with other mesoscale phenomena to produce or enhance convection.

Brundidge, K. C.↗

NASA NTRS1981

Dynamic phenomena in coronal flux tubes

The study of stellar atmospheres and the determination of specific physical mechanisms, geometries, and magnetic structures by which coronae are maintained is examined. Ultraviolet and soft X-ray components observed in the radiative output of cool stars and the Sun require counterentropic temperature gradients for their explanation. The existence of a hot corona is recognized as a result of mechanical or fluid dynamic effects and the importance of the magnetic field in the heating is accepted. Magnetohydrodynamic energy release associated with the emergence of magnetic flux through the chromosphere and its dynamic readjustment in the corona are major counterentropic phenomena which are considered as primary candidates for corona heating. Systematic plows in coronal flux tubes result from asymmetric heating and systematic flows can exist without substantial chromospheric pressure differences.

Mariska, J. T.↗

NASA NTRS1982

Laboratory studies of photochemical and spectroscopic phenomena related to comets

The relationship between laboratory observations and cometary phenomena is reviewed, with particular attention to how laboratory studies must be done to obtain all data needed for astronomical purposes. It is pointed out how supersonic expansion of the gas evaporating from the nucleus can affect the photochemical lifetime and the energy partitioning among the fragments. The use of the CS radical as a remote sensing probe of conditions in the inner coma is also discussed.

Jackson, W. M.↗

NASA NTRS1983

Interactive phenomena in supersonic jet mixing problems

The interactive phenomena that occur in the plume flowfield produced by a supersonic jet exhausting into a supersonic or subsonic external stream are discussed. A spatial marching parabolized Navier-Stokes approach is used to analyze the coupled viscous/inviscid interactive processes in supersonic flow regions. A 'partially parabolic' spatial marching procedure is used to analyze embedded subsonic regions (viz. the flow behind Mach discs) and the subsonic portion of the plume mixing layer for subsonic external flows. Coupling between the two-regions utilizes viscous-characteristic techniques and appropriate iterative procedures. Applications to a variety of jet mixing problems are presented. The importance of accounting for compressibility effects on the turbulence is demonstrated via comparisons of predictions employing several two-equation turbulence models with detailed laboratory data.

Dash, S. M.↗

NASA NTRS1981

Observations of dynamical phenomena in sunspots

A preliminary report of the results of one observing run based on data from one spectral line, the photospheric magnetic line Fe 6303, is presented as part of a series of observations of dynamical phenomena in sunspots using photographic spectra with the SPO vacuum tower telescope and echelle spectrograph. The ejection of a magnetic feature from the outer edge of the penumbra was observed. The initial total field strength of the feature was about 1000 gauss, which appeared to decrease as the feature moved away from the sunspot. The proper motion was about 2 km/s, and the velocity field measured in the V profile showed a downflow of 400 m/s on the spotward side of the moving magnetic feature. Umbral oscillations at the photospheric level with a herringbone structure characteristic of horizontally propagating waves, suggesting some overtone mode of membrane oscillation in the umbra, were seen. The peak amplitude of the oscillation was about 200 m/s, and the mean power spectrum had several clear peaks.

Nye, A. H.↗

NASA NTRS1983

Polar and auroral phenomena - A review of U.S. progress during 1979-1982

The quadrennium 1979-1982 has been a highly active time in the field of polar and auroral research, with nearly 400 research papers and thirty general or topical review papers written by U.S. authors. This paper highlights progress in understanding auroral morphology, precipitating particle fluxes, the spectra and sources of upward-flowing particles, large-scale Birkeland currents, and theoretical and experimental advances in auroral-scale electrodynamics. Global electrodynamics, active experiments, plasma waves, and auroral aeronomy, although certainly 'polar and auroral phenomena', are discussed in other papers in this issue.

Reiff, P. H.↗

NASA NTRS1984

Investigation of flow phenomena in a transonic fan rotor using laser anemometry

Several flow phenomena including flowfield periodicity, rotor shock oscillation, and rotor shock system geometry were investigated in a transonic low aspect ratio fan rotor using laser anemometry. Flow periodicity is found to increase with increasing rotor pressure rise, and to correlate with blade geometry variations. Analysis of time-accurate laser anemometer data indicates that the rotor shock oscillates about its mean location with an amplitude of 3 to 4 percent of rotor chord. The shock surface is nearly two-dimensional or levels of rotor pressure rise at and above the peak efficiency level but becomes more complex for lower levels of pressure rise. Spanwise shock lean generates radial flows due to streamline deflection in the hub-to-shroud streamsurface.

Strazisar, A. J.↗

NASA NTRS1983

Dependence of macrophysical phenomena on the values of the fundamental constants

Using simple arguments, it is considered how the fundamental constants determine the scales of various macroscopic phenomena, including the properties of solid matter; the distinction between rocks, asteroids, planets, and stars; the conditions on habitable planets; the length of the day and year; and the size and athletic ability of human beings. Most of the results, where testable, are accurate to within a couple of orders of magnitude.

Press, W. H.↗

NASA NTRS1984

A numerical weather prediction system designed to simulate atmospheric downburst phenomena

It is pointed out that an increase in the understanding of weather-related aircraft accidents can save hundreds of human lives and million of dollars. A better understanding regarding the interaction between aircraft operation and severe weather conditions can be obtained with the aid of flight simulator facilities. It is shown that numerical weather modeling is one of the most precise and cost-effective inputs for flight simulators in the long run. A comprehensive weather modeling system is being developed for the simulation of different scales of atmospheric phenomena. The modeling system utilizes two numerical weather models, including the Mesoscale Atmospheric Simulation system, and the Terminal Area Simulation System.

Chuang, S.↗

NASA NTRS1984

Stability of absorption phenomena in laser-thermal propulsion

The mean flow and stability characteristics of laser absorption phenomena in a choked converging-diverging nozzle are considered. Calculations are presented for a given nozzle geometry and a series of laser intensities. Gas absorptivities corresponding to a hydrogen-cesium mixture are used with different initial temperatures being selected to investigate the effects of changes in the shape of the k-T curve. Both stability and mean flow calculations are limited to the one-dimensional case. The mean flow results show a decrease in mass flow as laser power is increased, along with increasingly steep temperature profiles. Calculations span regions of partial and complete absorption. One region is found where multiple solutions exist. Local stability results indicate the u-c characteristic is the only unstable mode in the unheated case. Laser heat addition makes this mode more unstable and also destabilizes the u-characteristic. Numerical calculations of disturbance propagation show that the instability of the u-c disturbances is counteracted by their reflection to u + c disturbances at the upstream end. The growth of the u-disturbances is localized in regions where the temperature profile is steep and they are damped in other regions. The increasing destabilization that is observed with increased laser power is probably the reason for difficulty in obtaining converged mean flow solutions at high laser intensities.

Merkle, C. L.↗

NASA NTRS1985

Reversion phenomena of Cu-Cr alloys

Cu-Cr alloys which were given various aging and reversion treatments were investigated in terms of electrical resistivity and hardness. Transmission electron microscopy was one technique employed. Some results obtained are as follows: the increment of electrical resistivity after the reversion at a constant temperature decreases as the aging temperature rises. In a constant aging condition, the increment of electrical resistivity after the reversion increases, and the time required for a maximum reversion becomes shorter as the reversion temperature rises. The reversion phenomena can be repeated, but its amount decreases rapidly by repetition. At first, the amount of reversion increases with aging time and reaches its maximum, and then tends to decrease again. Hardness changes by the reversion are very small, but the hardness tends to soften slightly. Any changes in transmission electron micrographs by the reversion treatment cannot be detected.

Nishikawa, S.↗

NASA NTRS1982

Investigation of surface tension phenomena using the KC-135 aircraft

The microgravity environment of the KC-135 aircraft was utilized in three experiments designed to determine the following: (1) the feasibility of measuring critical wetting temperatures; (2) the effectiveness of surface tension as a means of keeping the cushioning heat transfer liquid in the furnace during ampoule translation; and (3) whether a non-wetting fluid would separate from the ampoule wall under low gravity conditions. This trio of investigations concerning surface phenomena demonstrates the effectiveness of the KC-135 as a microgravity research environment for small-scale, hand-held experiments.

Alter, W. S.↗

NASA NTRS1985

Analytical study of flow phenomena in SSME turnaround duct geometries

The SSME fuel turbopump hot gas manifold was identified as a source of loss and flow distortion which significantly affects the performance and durability of both the drive turbine and the LOX injector area of the main combustion chamber. Two current SSME geometries were studied, the full power level (FPL) and the first manned orbital flight (FMOF) configuration. The effects of turnaround duct geometry on flow losses and distortions, by varying wall curvature and flow area variation in the 180 deg turnaround region were examined. The effects of the duct inlet flow phenomena such as the radial distortion of the inlet flow and inlet swirl level on turnaround duct performance were also investigated. It is shown that of the two current geometries, the FMOF configuration had lower pressure losses and generated less flow distortion, but had a small flow separation bubble at the 180 deg turnaround exit. It is found that by optimizing wall curvature and flow diffusion in the turnaround, improved duct performance can be achieved.

Mclallin, K. L.↗

NASA NTRS1985

Nonlinear global stability analysis of compressor stall phenomena

Compressor stall phenomena are analyzed from the point of view of nonlinear control theory, based on bifurcation-catastrophe techniques. This new approach appears promising and offers insight into such well-known compressor instability problems as surge and rotating stall and suggests strategies for recovery. Three interlocking dynamic nonlinear state space models are developed. It is shown that the problem of rotating stall can be viewed as an induced bifurcation of solution of the unstalled model. Hysteresis effects are shown to exist in the stall/recovery process. Surge cycles are observed for some critical parameter values. The oscillatory behavior is seen to be due to development of limit cycles, generated by Hopf bifurcation of solutions. More specifically, it is observed that at certain critical values of parameters, a family of stable limit cycles with growning and then diminishing amplitudes is generated, then giving rise to an unstable family of limit cycles. This unstable family in turn bifurcates into other unstable families. To further illustrate the utility of the methodology, some partial computation of domains is carried out, and parameter sensitivity analysis is performed.

Razavi, H.↗

NASA NTRS1985

Recombination phenomena in high efficiency silicon solar cells

The dominant recombination phenomena which limit the highest efficiency attainable in silicon solar cells under terrestrial sunlight are reviewed. The ultimate achievable efficiency is limited by the two intrinsic recombination mechanisms, the interband Auger recombination and interband Radiative recombination, both of which occur in the entire cell body but principally in the base layer. It is suggested that an optimum (26%) cell design is one with lowly doped 50 to 100 micron thick base, a perfect BSF, and zero extrinsic recombination such as the thermal mechanism at recombination centers the Shockley-Read-Hall process (SRH) in the bulk, on the surface and at the interfaces. The importance of recombination at the interfaces of a high-efficiency cell is demonstrated by the ohmic contact on the back surface whose interface recombination velocity is infinite. The importance of surface and interface recombination is demonstrated by representing the auger and radiative recombination losses by effective recombination velocities. It is demonstrated that the three highest efficiency cells may all be limited by the SRH recombination losses at recombination centers in the base layer.

Sah, C. T.↗

NASA NTRS1985

Correlation between solar neutrino flux and other solar phenomena

A study was made of the solar neutrino data with a tank of CC14 located 4800 mwe underground for the period 1970 to 83. These observations are on the production rates of Ar37 atoms via the reaction upsilon sub e + Cl37 yields Ar37 plus e(-) in the tank caused presumably by a flux of neutrinos from the Sun. The idea of possible time variations in the data shown is discussed and an attempt is made to correlate the variations to two other phenomena of solar origin-the sunspot number and the geomagnetic Ap index.

Lal, S.↗