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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 253 records · Page 14
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NASA NTRS1974

Radio observations of two clusters of galaxies

Maps including the Coma and Hercules clusters of galaxies were made at 195, 318, and 611 MHz, and were compared with optical counts of galaxies in the clusters. An extended region of radio emission approximately 20 minutes in diameter was observed at the center of the Coma cluster. A distributed source region was also observed which appears to include the Hercules cluster, although the possibility that it is just an irregularity in the galactic foreground radiation cannot be completely ruled out.

Donivan, F. F., Jr.↗
NASA NTRS1974

Optical antenna gain. I - Transmitting antennas

The gain of centrally obscured optical transmitting antennas is analyzed in detail. The calculations, resulting in near- and far-field antenna gain patterns, assume a circular antenna illuminated by a laser operating in the TEM-00 mode. A simple polynomial equation is derived for matching the incident source distribution to a general antenna configuration for maximum on-axis gain. An interpretation of the resultant gain curves allows a number of auxiliary design curves to be drawn that display the losses in antenna gain due to pointing errors and the cone angle of the beam in the far field as a function of antenna aperture size and its central obscuration. The results are presented in a series of graphs that allow the rapid and accurate evaluation of the antenna gain which may then be substituted into the conventional range equation.

Klein, B. J.↗
NASA NTRS1974

Analysis of acoustic radiation in a jet flow environment

The analysis of sound fields from arbitrary source distributions in terms of Legendre and spherical Hankel functions is well known. The purpose of this paper is to extend this classical method of analysis to environments such as jet flows where flow and flow gradients are inherently present. The wave-equation governing the radiation of sound in such an environment is derived. The steady state flow and flow gradients in the axial and transverse directions appear as coefficients in the terms of the wave-equation. A semi-numerical method is used to solve the wave-equation in terms of modified spherical harmonics yielding the phase velocities and the directivities of an infinite set of modes. The directivity of each mode is obtained in terms of modified Legendre functions by numerical integration. Some results of these directivity and phase-velocity calculations are presented for a limited number of frequency and flow parameters. Both convective and shear refraction are shown to be important.

Mungur, P.↗
NASA NTRS1974

Estimate of heat fluxes on the subjacent surface (according to data from synoptic analysis)

Several methods of estimating heat fluxes from nonadiabatic sources distributed over a subjacent surface were discussed. Data calculated by synoptic analysis for the entire Northern Hemisphere from aerological soundings at the AT500 and AT400 level, along with the temperature of the subjacent surfaces, were used. A polytropic model of the atmosphere is used in order to avoid the problems posed by the lack of any complete theory of heat transfer in the lower atmosphere.

Nagurnyy, A. P.↗
NASA NTRS1975

Electromagnetic hiss and relativistic electron losses in the inner zone

It is shown that ELF hiss is present in the inner radiation zone (L less than 2) during both storms and substorms. This presence is ascribed to propagation of waves into this region from a distributed source located at high altitude near the equatorial plasmapause. Two major effects allow hiss to reach the inner zone during storms and substorms: (1) the observed tendency for plasmaspheric hiss to be greatly intensified during the recovery phase as the outward-moving plasmapause encounters the electrons that have been freshly injected into the magnetosphere; (2) the displacement of the plasmapause, and the presumed source region, to low altitudes during high levels of magnetic activity.

Tsurutani, B. T.↗
NASA NTRS1975

Duct acoustics and acoustic finite element method

A comprehensive solution method - Acoustic Finite Element Method - has been proposed. In order to generate confidence in the method proposed, the problem of influence of shear flow in a two-dimensional channel on sound propagation from an arbitrary source distribution has been theoretically formulated. From the preliminary investigation of application of acoustic finite element method, it seems that it can provide solutions to problems concerning the transmission of sound in variable area ducts, or in ducts in which the boundary layer depends on the streamwise variable, or in ducts with discontinuities in lining impedance and with end termination impedances, both the inlet and exhaust jet flows being taken into account.

Kapur, A.↗
NASA NTRS1977

Swept wing aerodynamics

Technique analyzes viscosity-dependent aerodynamic characteristics of multielement infinite swept wings in incompressible flow. Use of source distributions rather than displacement thickness to represent boundary layer effect on potential flow and of iterative technique for matrix inversion reduces computer time for overall analysis.

Dvorak, F. A.↗
NASA NTRS1976

Terrestrial kilometric radiation: 1: Spatial structures studies

Observations are presented of lunar occultations of the earth at 250 kHz obtained with the Radio-Astronomy-Explorer-2 satellite which were used to derive two dimensional maps of the location of the sources of terrestrial kilometric radiation (TKR). By examining the two dimensional source distributions as a function of the observer's location (lunar orbit) with respect to the magnetosphere, the average three dimensional location of the emission regions can be estimated. Although TKR events at 250 kHz can often be observed at projected distances corresponding to the 250 kHz electron gyro or plasma level (approximately 2 earth radii), many events are observed much farther from the earth (between 5 and 15 earth radii). Dayside emission apparently in the region of the polar cusp and the magnetosheath and night emission associated with regions of the magnetotail are examined. The nightside emission is suggestive of a mechanism involving plasma sheet electron precipitation in the pre-midnight sector.

Alexander, J. K.↗
NASA NTRS1976

Application of the adaptive-wall concept to three-dimensional low-speed wind tunnels

Three methods for evaluating the functional relationships required to obtain interference-free flows about a model in a wind tunnel have been developed. The first, the original multipole expansion (MPE) procedure, is based on a series of point singularities which satisfy the governing Prandtl-Glauert equation. The second, the modified MPE, provides an improved representation of finite-span wings and thereby extends the range of validity of the original MPE to larger ratios of span-to-control-surface-width. The third method is more general and is based on source distributions over the control surface. Several numerical examples are presented to help establish the range of validity of these methods. An accuracy-assessment procedure, which combines the original MPE procedure with classical wall-correction theory, has been developed to estimate the degree of interference at the model if the functional relationships are not satisfied exactly. Several numerical examples are presented for representative wings and bodies.

Erickson, J. C., Jr.↗
NASA NTRS1976

Noise propagation in urban and industrial areas

Noise propagation in streets and the discrepancies between theoretical analyses and field measurements are discussed. A cell-model is used to estimate the general background level of noise due to vehicular sources distributed over the urban area.

Davies, H. G.↗
NASA NTRS1976

Terrestrial kilometric radiation. I - Spatial structure studies

Observations of lunar occultations of earth at 250 kHz, obtained with the Radio Astronomy Explorer 2 satellite, have been used to derive two-dimensional maps of the location of the sources of terrestrial kilometric radiation (TKR). By examining the two-dimensional source distributions as a function of the observer's location (lunar orbit) with respect to the magnetosphere, the average three-dimensional location of the emission regions can be estimated. Although TKR events at 250 kHz can often be observed at projected distances corresponding to the 250-kHz electron gyro or plasma level (about 2 earth radii), many events are observed much farther from earth (about 5 to 15 radii). On the dayside, emission was apparently observed in the region of the polar cusp and the magnetosheath at a magnetic latitude of about 70 deg; in the night hemisphere, emission is found to be associated with regions of the magnetotail at latitudes of at least 70 deg. The nightside emission is suggestive of a mechanism involving plasma-sheet electron precipitation in the premidnight sector.

Alexander, J. K.↗
NASA NTRS1977

Ultra-heavy cosmic rays: Theoretical implications of recent observations

Extreme ultraheavy cosmic ray observations (Z greater or equal 70) are compared with r-process models. A detailed cosmic ray propagation calculation is used to transform the calculated source distributions to those observed at the earth. The r-process production abundances are calculated using different mass formulae and beta-rate formulae; an empirical estimate based on the observed solar system abundances is used also. There is the continued strong indication of an r-process dominance in the extreme ultra-heavy cosmic rays. However it is shown that the observed high actinide/Pt ratio in the cosmic rays cannot be fit with the same r-process calculation which also fits the solar system material. This result suggests that the cosmic rays probably undergo some preferential acceleration in addition to the apparent general enrichment in heavy (r-process) material. As estimate also is made of the expected relative abundance of superheavy elements in the cosmic rays if the anomalous heavy xenon in carbonaceous chondrites is due to a fissioning superheavy element.

Blake, J. B.↗
NASA NTRS1978

Airfoil profile in a nonuniform flow

A theory of airfoil section past two dimensional nonuniform flow is developed. The theory is based on representation of airfoil section by vortex and source distributions and it can be used for calculation of aircraft wings in homogeneous and inhomogeneous flow, as well as for calculation of straight and radial blade and vane-cascades.

Polasek, J.↗
NASA NTRS1978

Three-dimensional effects on pure tone fan noise due to inflow distortion

Two dimensional, quasi three dimensional and three dimensional theories for the prediction of pure tone fan noise due to the interaction of inflow distortion with a subsonic annular blade row were studied with the aid of an unsteady three dimensional lifting surface theory. The effects of compact and noncompact source distributions on pure tone fan noise in an annular cascade were investigated. Numerical results show that the strip theory and quasi three-dimensional theory are reasonably adequate for fan noise prediction. The quasi three-dimensional method is more accurate for acoustic power and model structure prediction with an acoustic power estimation error of about plus or minus 2db.

Kobayashi, H.↗
NASA NTRS1978

Aircraft noise propagation

Sound diffraction experiments conducted at NASA Langley Research Center to study the acoustical implications of the engine over wing configuration (noise-shielding by wing) and to provide a data base for assessing various theoretical approaches to the problem of aircraft noise reduction are described. Topics explored include the theory of sound diffraction around screens and wedges; the scattering of spherical waves by rectangular patches; plane wave diffraction by a wedge with finite impedence; and the effects of ambient flow and distribution sources.

Hadden, W. J.↗
NASA NTRS1978

Hard X-ray imaging from the solar probe

The solar probe offers a platform with particular advantages for studying solar nonthermal plasma processes via the observations of hard X-radiation from energetic electrons in the chromosphere and corona, these include (1) high sensitivity, (2) a second line of sign (in addition to the earth's) that can aid in three dimensional reconstruction of the source distribution, and, (3) the possibility of correlation with direct measurements of the nonthermal particles from the probe itself.

Hudson, H. S.↗
NASA NTRS1977

Finite-element solutions for geothermal systems

Vector potential and scalar potential are used to formulate the governing equations for a single-component and single-phase geothermal system. By assuming an initial temperature field, the fluid velocity can be determined which, in turn, is used to calculate the convective heat transfer. The energy equation is then solved by considering convected heat as a distributed source. Using the resulting temperature to compute new source terms, the final results are obtained by iterations of the procedure. Finite-element methods are proposed for modeling of realistic geothermal systems; the advantages of such methods are discussed. The developed methodology is then applied to a sample problem. Favorable agreement is obtained by comparisons with a previous study.

Chen, J. C.↗
NASA NTRS1978

Measurements of noise produced by flow past lifting surfaces

Wind tunnel studies have been conducted to determine the specific locations of aerodynamic noise production within the flow field about various lifting-surface configurations. The models tested included low aspect ratio shapes intended to represent aircraft flaps, a finite aspect ratio NACA 0012 wing, and a multi-element wing section consisting of a main section, a leading edge flap, and dual trailing edge flaps. Turbulence was induced on the models by surface roughness. Lift and drag were measured for the flap models. Hot-wire anemometry was used for study of the flap-model vortex roll-up. Apparent noise source distributions were measured by use of a directional microphone system, located outside the tunnel, which was scanned about the flow region to be analyzed under computer control. These distributions exhibited a diversity of pattern, suggesting that several flow processes are important to lifting-surface noise production. Speculation concerning these processes is offered.

Kendall, J. M.↗