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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Bipolar Ejection of Matter from Hot Stars

A general program on the internal velocities in H II regions was carried out within the past decade by the use of photographic Fabry-Perot interferometry, in the H (alpha) line and lately also in the N IIlambda 6584 line. Among the score of objects studied three H II regions and one planetary nebula possess pronounced symmetry around their ionizing stars. Velocity data combined with morphological properties suggest strongly that the nebulae were formed essentially by matter ejected from the central star and that ejection occurred preferentially from diametrially opposite regions on the star, that is, in a bi-polar fashion. The nebulae are discussed individually and a model for the ejection mechanism is presented.

Pismis, P.↗
NASA NTRS1984

Detection of Solar Gravity Mode Oscillations

An analysis of solar velocity data obtained at the Stanford Solar Observatory has shown the existence of solar global oscillations. The oscillations are in the range 45 to 105 micro Hz (160 to 370 minutes) and are interpreted as internal gravity modes of degree l=1 and l=2.

Scherrer, P. H.↗
NASA NTRS1984

Numerical experiments on galaxy clustering in open universes

Numerical studies were performed on the dynamical effects on the evolution of clumps, filaments, voids, and galaxy clusters by various final Omega values. The final Omega values examined ranged from 0.03-1, and attention was given to defining observations of superclusters which would aid in determining an actual value for Omega. The numerical trials consisted of n-body integration programs governed by the total expansion and final Omega value and included comparisons between results for open and closed universes. All runs started from the same initial conditions. The dispersion trajectories of particles and the final galactic cluster forms were found to be equivalent, regardless of the final Omega value. The possibility of deriving a value for Omega from velocity data on galaxies which have not yet joined clusters is discussed.

Miller, R. H.↗
NASA NTRS1984

The many faces of Capella - A search for rotational modulations and a study of systematic velocities of emission lines in the ultraviolet

The UV spectra of Capella were monitored for fluctuations using IUE instrumentation, and radial velocities of the emission lines were determined. The possible fluctuations were studied from March through April 1981, and radial velocity data were taken over six days in 1982. The Capella surface activity emissions proved to be steady, while redshifts from high excitation were found in the photospheric plasma. Downflows of 100,000 K plasma in the stellar transition zone could produce the redshifts. The FWHMs of the emission lines exceeded the redshift by an order of magnitude, suggesting that the observed excitations could be only averaged values of the dynamics of the outer atmosphere of Capella.

Ayres, T. R.↗
NASA NTRS1985

Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area. V - Luminosity functions of Virgo Cluster galaxies

The present catalog of 2096 galaxies within an area of about 140 sq deg approximately centered on the Virgo cluster should be an essentially complete listing of all certain and possible cluster members, independent of morphological type. Cluster membership is essentially decided by galaxy morphology; for giants and the rare class of high surface brightness dwarfs, membership rests on velocity data. While 1277 of the catalog entries are considered members of the Virgo cluster, 574 are possible members and 245 appear to be background Zwicky galaxies. Major-to-minor axis ratios are given for all galaxies brighter than B(T) = 18, as well as for many fainter ones.

Binggeli, B.↗
NASA NTRS1986

Laser velocimetry in highly three-dimensional and vortical flows

The need for experimentally determined 3-D velocity information is crucial to the understanding of highly 3-dimensional and vortical flow fields. In addition to gaining an understanding of the physics of flow fields, a correlation of velocity data is needed for advanced computational modelling. A double pass method for acquiring 3-D flow field information using a 2-D laser velocimeter (LV) is described. The design and implementation of a 3-D LV with expanded capabilities to acquire real-time 3-D flow field information are also described. Finally, the use of such an instrument in a wind tunnel study of a generic fighter configuration is described. The results of the wind tunnel study highlight the complexities of 3-D flow fields, particularly when the vortex behavior is examined over a range of angles of attack.

Novak, C. J.↗
NASA NTRS1986

Constraints on galaxy formation theories

The present theories of galaxy formation are reviewed. The relation between peculiar velocities, temperature fluctuations of the microwave background and the correlation function of galaxies point to the possibility that galaxies do not form uniformly everywhere. The velocity data provide strong constraints on the theories even in the case when light does not follow mass of the universe.

Szalay, A. S.↗
NASA NTRS1986

The mass of the Coma cluster

Mass estimate uncertainties for the Coma cluster in position and velocity data for the galaxies are examined under the assumption that mass and galaxy distribution are parallel, on the one hand, and on the other, that the form of the mass distribution is not constrained. While low mass models have all the mass in the cluster core, and require the galaxies to be on or near circular orbits, high mass models are noted to have weakly concentrated mass distributions and primarily radial orbits. It is concluded that galaxy data alone are unlikely to clearly distinguish between these possibilities.

The, Lih Sin↗
NASA NTRS1987

Studies of calcium emission stars. I - HD 158393 a giant star in a binary system

HD 158393 is a giant star of spectral type late G or early K which has moderately strong Ca II H and K emission cores. UBVRIJHK photometry and IUE spectra reveal a companion of type F0-F2, luminosity class IV or V. Radial velocity data yield an orbit with a period of 31 day. The K and F stars have nearly equal mass, with a minimum value of 1.7 solar masses if i of less than 72 deg is adopted, as required by the absence of eclipses. The strong Ca II emission indicates the enhanced chromospheric activity which is typical of giant stars in a binary system of this period, and the light is variable in a 31-day period, indicative of synchronous rotation as well as on a long time-scale. Analysis of the 31-day light period by fitting a spot model indicates the presence of two spots in 1975 and 1976; the major spot appears to have been present throughout the observing period (1973-1981). The potential confusion caused by the presence of the second spot for part of the observing period emphasizes the importance of fitting a model if the photometric period is to be understood in terms of the synchronous rotation. The two spots showed different periods and were at different latitudes, suggesting differential rotation of the giant star.

Evans, T. Lloyd↗
NASA NTRS1988

Experimental measurements in a large separation bubble due to a simulated glaze ice shape

The effect of a simulated glaze ice accretion on the aerodynamic performance of a NACA 0012 airfoil was studied experimentally. Two ice shapes were tested, one from an experimentally measured accretion and one from an accretion predicted using a computer model given the same icing conditions. Lift, drag and moment coefficients were measured for the airfoil with both ice shapes, smooth and rough. The aerodynamic performance of the two shapes compared well at positive, but not negative, angles of attack. Split hot-film probe velocity data were presented in the upper surface boundary layer and in the wake. Boundary layer parameters were presented for the separation bubble and in the reattached turbulent boundary layer.

Bragg, M. B.↗
NASA NTRS1988

Conduction-driven chromospheric evaporation in a solar flare

Observations of gentle chromospheric evaporation during the cooling phase of a solar flare are presented. Line profiles of the low-temperature (T of about 6 x 10 to the 6th K) coronal Mg XI line, observed with the X-Ray Polychromator on the Solar Maximum Mission, show a blueshift that persisted for several minutes after the impulsive heating phase. This result represents the first detection of an evaporation signature in a soft X-ray line formed at this low temperature. By combining the Mg XI blueshift velocity data with simultaneous measurements of the flare temperature derived from Ca XIX observations, it is demonstrated that the upward flux of enthalpy transported by this gently evaporating plasma varies linearly with the downward flux of thermal energy conducted from the corona. This relationship is consistent with models of solar flares in which thermal conduction drives chromospheric evaporation during the early part of the cooling phase.

Zarro, Dominic M.↗
NASA NTRS1988

Integrated-light spectroscopy of globular clusters at the infrared Ca II lines

Integrated-light spectroscopy has been obtained for 27 globular clusters at the Ca II IR triplet. Line strengths and radial velocities have been measured from the spectra. For the well-studied clusters in the sample, the strength of the Ca II lines is very well correlated with previous metallicity estimates. Thus, the triplet is useful as a metallicity indicator in globular cluster integrated-light spectra. The greatly reduced effect of interstellar extinction at these wavelengths (compared to the blue region of the spectrum) has permitted observations of some of the most heavily reddened clusters in the Galaxy. For several such clusters, the Ca II triplet metallicities are in poor agreement with metallicity estimates from IR photometry by Malkan (1981). The strength of an interstellar band at 8621A has been used to estimate the amount of extinction towards these clusters. Using the new metallicity and radial-velocity data, the metallicity distribution, kinematics, and spatial distribution of the disk globular cluster system have been analyzed. Results very similar to those of Zinn (1985) have been found. The relation of the disk globulars to the stellar thick disk is discussed.

Armandroff, Taft E.↗
NASA NTRS1988

Turbofan forced mixer lobe flow modeling. 1: Experimental and analytical assessment

A joint analytical and experimental investigation of three-dimensional flowfield development within the lobe region of turbofan forced mixer nozzles is described. The objective was to develop a method for predicting the lobe exit flowfield. In the analytical approach, a linearized inviscid aerodynamical theory was used for representing the axial and secondary flows within the three-dimensional convoluted mixer lobes and three-dimensional boundary layer analysis was applied thereafter to account for viscous effects. The experimental phase of the program employed three planar mixer lobe models having different waveform shapes and lobe heights for which detailed measurements were made of the three-dimensional velocity field and total pressure field at the lobe exit plane. Velocity data was obtained using Laser Doppler Velocimetry (LDV) and total pressure probing and hot wire anemometry were employed to define exit plane total pressure and boundary layer development. Comparison of data and analysis was performed to assess analytical model prediction accuracy. As a result of this study a planar mixed geometry analysis was developed. A principal conclusion is that the global mixer lobe flowfield is inviscid and can be predicted from an inviscid analysis and Kutta condition.

Barber, T.↗
NASA NTRS1987

A comparison of turbulence measurement methods

An experiment is described in which temperature (density) and velocity are measured separately but simultaneously as functions of time so that it is possible to determine the relationships among velocity, density, and the product of density and velocity. Temperatures were measured with a dual-wire thermocouple probe. Velocity data were supplied by a fringe laser-Doppler anemometer. Signals from thermocouples and the laser were recorded on FM magnetic tape for later processing.

Fralick, Gustave C.↗
NASA NTRS1988

Hot wire anemometer measurements in the unheated air flow tests of the SRB nozzle-to-case joint

Hot-Wire Anemometer measurements made in the Solid Rocket Booster (SRB) nozzle-to-case joint are discussed. The study was undertaken to glean additional information on the circumferential flow induced in the SRB nozzle joint and the effect of this flow on the insulation bonding flaws. The tests were conducted on a full-scale, 2-D representation of a 65-in long segment of the SRB nozzle joint, with unheated air as the working fluid. Both the flight Mach number and Reynolds number were matched simultaneously and different pressure gradients imposed along the joint face were investigated. Hot-wire anemometers were used to obtain velocity data for different joint gaps and debond configurations. The procedure adopted for hot-wire calibration and use is outlined and the results from the tests summarized.

Ramachandran, N.↗
NASA NTRS1988

A performance/loss evaluation of SSME HPFTP turbine

An evaluation of component losses of the High Pressure Fuel Turbopump (HPFTP) in the Space Shuttle Main Engine (SSME) is performed using a mean-line prediction method. This is accompanied with an extensive review of loss correlations in the literature. The present prediction uses an existing gas path velocity triangle, real LH2 and H2O gas properties and loss correlations selected from the literature. The significant losses incurred in the HPFTP turbine include profile loss, secondary loss, and tip clearance loss. Results obtained from the present prediction are compared to those calculated from a quasi-three dimensional numerical analysis. Except for the clearance loss, the present loss coefficients are in general higher than their counterparts from the quasi-three dimensional analysis. The fact that the mean-line velocity data being unable to represent actual flow fields near the hub and the tip regions is largely responsible for the uncertainty involved in the present method. On the other hand, due mainly to the ad-hoc nature of the studies involved, the correlations currently available in the literature may not be suitable for accurate loss prediction of the particular rocket turbine in the SSME HPFTP. Further studies particularly in the areas of tip clearance loff, coolant loss, secondary loss, and their interactions are desirable. Fundamental phenomena concerning flow unsteadiness in wake shedding and turbulence are also important.

Chyu, Mingking K.↗
NASA NTRS1989

Separated flows developing under increasingly adverse pressure gradients

Experimental results are presented for separating flows over a NASA GA(W)-1 airfoil with 2-percent trailing-edge thickness, with emphasis on the mean velocity data that demonstrate flowfield similarity downstream of separation. The length scale presently employed was selected because it furnishes the requisite matching point between the outer, mixing region flow and the back-flow.

Mehta, Jayesh M.↗
NASA NTRS1988

Optical matrix-vector processing for computational fluid dynamics

An optical processor to solve partial differential equations for computational fluid dynamics applications is considered. This application is new and original for optical processors. The algorithms that are used are optical realizations of the Newton-Raphson method for nonlinear equations and a new optical LU direct decomposition and Gauss-Seidel iterative solution to the resultant linear algebraic equations. These algorithms are used to solve Burger's equation (a specific form of the momentum equation in fluid dynamics). The nonlinear equations provide 1-D velocity data at each time step. Simulation results of optical processing with these algorithms on computational fluid dynamics data is included.

Perlee, Caroline J.↗