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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Calculation of confined swirling flows

Swirling jets are an important constituent flow of many types of combustion equipment. Flame size, shape, stability and combustion intensity are all favorably influenced by swirling some portion of the incoming air with the fuel. Fluid dynamics computer codes are being developed for the mathematical simulation of flows in practical combustors. It is important that these codes have the ability to accurately and reliably calculate swirling flows. Turbulent flow calculations with swirl can be inaccurate due to at least three major reasons: limitations of the turbulence modeling used, incorrect or inadequate specifications of inlet boundary conditions, and, error introduced through the numerics. These sources of error are described, and examples provided of each. The state-of-the-art in such calculations is reviewed. The controlling character of current numerics is demonstrated, and it is concluded that as a first priority, better numerics must be arrived at, and that an improved understanding of the discharge flow from swirl generators is essential as a second priority. When these priorities are satisfied an improved turbulence model is desirable. It is also concluded that an improved understanding of swirl-induced recirculation would be an asset.

Sturgess, G. J.↗
NASA NTRS1986

Influence of large-scale motion on turbulent transport for confined coaxial jets. Volume 1: Analytical analysis of the experimental data using conditional sampling

The existence of large scale coherent structures in turbulent shear flows has been well documented. Discrepancies between experimental and computational data suggest a necessity to understand the roles they play in mass and momentum transport. Using conditional sampling and averaging on coincident two component velocity and concentration velocity experimental data for swirling and nonswirling coaxial jets, triggers for identifying the structures were examined. Concentration fluctuation was found to be an adequate trigger or indicator for the concentration-velocity data, but no suitable detector was located for the two component velocity data. The large scale structures are found in the region where the largest discrepancies exist between model and experiment. The traditional gradient transport model does not fit in this region as a result of these structures. The large scale motion was found to be responsible for a large percentage downstream at approximately the mean velocity of the overall flow in the axial direction. The radial mean velocity of the structures was found to be substantially greater than that of the overall flow.

Brondum, D. C.↗
NASA NTRS1986

Numerical and experimental investigation of nonswirling and swirling confined jets

An investigation of the influence of large scale structures on the flow development for coaxial jets with sudden expansion (with and without swirl) is presented. Both an experimental study and numerical predictions were performed for a configuration corresponding to that considered by Johnson and Bennett and Roback and Johnson. The effects of large scale structures on the swirling and nonswirling flows are documented, in particular their influence on turbulence modeling and the numerical simulation. The ensemble-averaged, time-dependent Navier-Stokes equations are solved by an LBI procedure to predict the turbulent flow field. Effects of artificial dissipation and placement of the upstream boundary in the numerical computation are also discussed.

Brondum, D. C.↗
NASA NTRS1986

Mass and momentum turbulent transport experiments with swirling confined coaxial jets. II

An experimental study of mixing downstream of swirling coaxial jets discharging into an expanded duct was conducted to obtain data for the evaluation and improvement of turbulent transport models currently used in a variety of computational procedures throughout the combustion community. A combination of laser velocimeter and laser induced fluorescence techniques was employed to obtain mean and fluctuating velocity and concentration distributions at selected axial and radial locations throughout the flow field. Flow visualization techniques were also employed to determine qualitatively the time dependent characteristics of the flow and the scale of turbulence. Simultaneous two component velocity and concentration/velocity measurements provided data which were used to determine the average momentum and mass transport rates for each of three measurement planes. Mixing for swirling flows occurred in several steps of axial and radial mean convective flow and was completed in one-third the length required for nonswirling flow. Comparison of the mass and momentum transport processes for swirling and nonswirling flows indicated that large differences existed in these processes between the two flows.

Roback, R.↗
NASA NTRS1986

A spatially confined long-lived stream of solar particles

The intensities of low-energy solar-interplanetary electrons and ions at 1 AU occasionally change in a 'square-wave' fashion. The changes may be increases or decreases and they have duration of a few hours. In one such example following a solar flare, particles flow away from the sun in a well-defined channel 2.5 x 10 to the 6th km in width for twenty hours or longer. It is believed that the interplanetary magnetic lines defined by this channel connect to an active region at 16 deg N solar latitude. At this time the earth was located at a solar latitude of 2 deg S. Evidently the particle channel connects to a region of the solar atmosphere which supplies particles over these long times either via storage of the flare accelerated particles or else by continuous acceleration. Arguments are given against the latter possibility. A model for coronal storage which is consistent with the observations is discussed.

Anderson, K. A.↗
NASA NTRS1986

Confining hot spots in 3C 196 - Implications for QSO-companion galaxies

VLBI observations of the extremely compact hot spot in the northern radio lobe of the QSO 3C 196 reveal the angular size of its smallest substructure to be 0.065 arcsec x 0.045 arcsec or about 300 pc at the redshift distance. The morphology of the hot spot and its orientation relative to the more diffuse radio emission suggest that it is formed by an oblique interaction between the nuclear QSO jet and circum-QSO cloud. The inferred density in this cloud, together with its apparent size, imply that the cloud contains a galactic mass, greater than a billion solar masses of gas. The effect of the jet will be to hasten gravitational collapse of the cloud. If many QSOs such as 3C 196 are formed or found in gas-rich environments, the QSO radio phase may commonly stimulate the metamorphosis of circum-QSO gas to QSO-companion galaxies or it may play a significant part in catalyzing star formation in existing companions.

Brown, R. L.↗
NASA NTRS1986

The bird: A pressure-confined explosion in the interstellar medium

The non-thermal radio continuum source G5.3-1.0, mapped at 20 cm with the Very Large Array (VLA) by Becker and Helfand, has an unusual bird-like shape. In order to determine possible interaction of this source with adjacent cold gas, we have mapped this region in the J=1-0 line of CO using the AT and T Bell Laboratories 7m antenna and the FCRAO 14m antenna. The map shown contains 1859 spectra sampled on a 1.5 arcminute grid; each spectrum has an rms noise of 0.2 K in 1 MHz channels. There are several molecular clouds at different velocities along the line of sight. The outer regions of a previously unknown Giant Molecular Cloud (GMC) at l=4.7 deg., b=-0.85 deg., v=200 km s(-1) appears to be interacting with G5.3-10: the molecular cloud has a bird-shaped hole at the position of the continuum source, except that the brightest continuum point (the bird's head) appears to be embedded in the cloud. The velocity of this GMC indicates it is within 2 kpc of the galactic center. The morphology suggests that a supernova or other explosive event occurred near the outside of the GMC, in a region where (n) is approximately 300 cm(-3), and expanded into a region of lower density and pressure. The pressures, densities, and velocity gradients of molecular clouds near the galactic center are on average higher than those of clouds near the Sun. We therefore expect that Type II supernovae near the galactic center would be distorted by their interactions with their parent molecular clouds.

Lane, A. P.↗
NASA NTRS1988

Dispersion, damping and confinement of propagating pulses in large space structures

Pulse propagations in large space structures caused by repeated pulse excitations are studied analytically (by using the Z-transforms) and numerically. It is found that resonance regimes can be generated not only by periodical, but also by non-periodical repeated pulses; the conditions for such regimes are derived. Special attention is paid to the dispersion of propagating pulses due to structural irregularities, to damping of pulses due to appropriate combination of elastic and viscous properties of joints between structural members, and to the protection of certain areas of Large Space Structures (LSS) from impacts provided by a pulse trapping effect.

Zak, Michail↗
NASA NTRS1988

Lateral optical confinement of channeled-substrate-planar lasers with GaAs/AlGaAs substrates

A physical explanation of the lateral guiding mechanism in channeled-substrate-planar (CSP) lasers based on the amount of wavefront tilt of the transverse field outside the channel region is presented. Because of this inherent wavefront tilt, all CSP lasers will have a very slight asymmetry in their transverse far-field pattern. The nature of the guiding mechanism does not require light absorption by the substrate. Design curves showing the complex lateral effective index step as a function of n-clad thickness with the active layer as a parameter are also presented. Depending on the specific layer compositions and thicknesses, the CSP guiding mechanism can provide a positive lateral index step for substrates with mole fractions of AlAs ranging from 0 to higher than 0.2.

Evans, Gary A.↗
NASA NTRS1988

On the pulsational overstability in narrowly confined viscous rings

Viscous accretion disks and rings are subject to pulsational overstability if the effective viscous stress is a rapidly increasing function of the disks' (or rings') surface density. Such a phenomenon is induced by the transfer of energy from shear to normal mode oscillations through viscous stress. The paper examines the global response of viscous accretion disks or rings to pulsational overstabilities. The analytic and preliminary numerical results indicate that all modes with wavelength longer than the scale height of the disk or ring are overstable. From the results, some examples of the complex time-dependent structure which may be induced by this overstability are illustrated. Finally, results are applied to narrow planetary rings to address the issues of maintenance of uniform precession and origin of eccentricity.

Papaloizou, J. C. B.↗
NASA NTRS1989

Surface Tension Confines Cryogenic Liquid

New type of Dewar provides passive, constant-temperature cryogenic cooling for scientific instruments under normal-to low-gravity conditions. Known as Surface-Tension-Contained Liquid Cryogen Cooler (STCLCC), keeps liquid cryogen in known location inside the Dewar by trapping liquid inside spongelike material. Unique sponge material fills most of volume of inner tank. Sponge is all-silica, open-cell material similar to that used for Space Shuttle thermal-protection tiles.

Castles, Stephen H.↗
NASA NTRS1988

Axisymmetric confined turbulent jet directed towards the liquid surface from below

A numerical simulation is presented of an axisymmetric turbulent jet discharging axially from below into a cylindrical tank and directed towards the liquid vapor interface. The liquid vapor interface is assumed to be flat and shear free. The k-epsilon turbulence model is used to calculate the eddy viscosity. The turbulence intensity distribution and the length scale associated with the k-epsilon model are calculated as functions of jet flow rates and systems parameters. Numerical results are compared with appropriate experimental data. The problems associated with the free surface boundary conditions for the turbulent quantities are discussed.

Hasan, Mohammad M.↗
NASA NTRS1989

Surface tension confined liquid cryogen cooler

A cryogenic cooler is provided for use in craft such as launch, orbital, and space vehicles subject to substantial vibration, changes in orientation, and weightlessness. The cooler contains a small pore, large free volume, low density material to restrain a cryogen through surface tension effects during launch and zero-g operations and maintains instrumentation within the temperature range of 10 to 140 K. The cooler operation is completely passive, with no inherent vibration or power requirements.

Stephen H Castles↗
NASA NTRS1989

Axisymmetric confined turbulent jet directed towards the liquid surface from below

A numerical simulation is presented of an axisymmetric turbulent jet discharging axially from below into a cylindrical tank and directed towards the liquid vapor interface. The liquid vapor interface is assumed to be flat and shear free. The k-epsilon turbulence model is used to calculate the eddy viscosity. The turbulence intensity distribution and the length scale associated with the k-epsilon model are calculated as functions of jet flow rates and systems parameters. Numerical results are compared with appropriate experimental data. The problems associated with the free surface boundary conditions for the turbulent quantities are discussed.

Hasan, Mohammad M.↗
NASA NTRS1990

Removing Burrs In Confined Spaces

Special tool proposed to remove burrs on ring edges left by operations of hollow mill near bases of round posts. Conceived because posts placed so closely together that ordinary and makeshift tools damage adjacent posts and difficult or impossible to use in narrow, deep spaces surrounding edges to be deburred. Designed specifically for use on hollow liquid-oxygen-injector posts of spacecraft engine, general tool concept adaptable to similar deburring problems on otherwise inaccessible parts.

Windbiel, Friedrich↗
NASA NTRS1990

Borescope Aids Welding In Confined Spaces

Welding torch holds video borescope to give operator view of workpiece in enclosed space. Operator sees clear, magnified image on video monitor and manipulates torch accordingly, despite visual obstruction presented by enclosure. Tinted shield tilted up while torch being positioned, then down to block excess light during welding. Reduces welding time by 50 percent, and increases quality of weld substantially.

Carrasco, Eddie↗