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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 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

High spatial resolution 10 micron imaging of IRC + 10216

Precise high-resolution 10-micron images of the carbon star IRC + 10216 have been obtained with a scanned linear array. The low noise and high dynamic range of these images permit deconvolution of the telescope point-spread function, revealing the radial brightness distribution of the circumstellar dust shell: approximate reflection symmetry is found in west-east scans, with a distinct division into two components of diameter about 0.40 and 2.2 arcsec. It is shown that this morphology is consistent with published interferometric data that had cast doubt upon an earlier, idealized two-component model. The observed brightness distribution implies that the circumstellar dust density may deviate substantially from the 1/r squared radial dependence expected for spherically symmetric outflow with constant velocity and constant rate of mass loss.

Bloemhof, E. E.↗
NASA NTRS1992

Distribution of ULF energy (f is less than 80 mHz) in the inner magnetosphere - A statistical analysis of AMPTE CCE magnetic field data

Magnetic field measurements made with the AMPTE CCE spacecraft are used to investigate the distribution of ULF energy in the inner magnetosphere. The data base is employed to examine the spatial distribution of ULF energy. The spatial distribution of wave power and spectral structures are used to identify several pulsation types, including multiharmonic toroidal oscillations; equatorial compressional Pc 3 oscillations; second harmonic poloidal oscillations; and nightside compressional oscillations. The frequencies of the toroidal oscillations are applied to determine the statistical radial profile of the plasma mass density and Alfven velocity. A clear signature of the plasma pause in the profiles of these average parameters is found.

Takahashi, Kazue↗
NASA NTRS2000

Effect of Melt Convection at Various Gravity Levels and Orientations on the Forces Acting on a Large Spherical Particle in the Vicinity of a Solidification Interface

Numerical modeling was Undertaken to analyze the influence of both radial and axial thermal gradients on convection patterns and velocities claiming solidification of pure Al and an Al-4 wt% Cu alloy. The objective of the numerical task was to predict the influence of convective velocity on an insoluble particle near a solid/liquid (s/l) interface. These predictions were then be used to define the minimum gravity level (q) required to investigate the fundamental physics of interactions between a particle and a s/l interface. This is an ongoing NASA founded flight experiment entitled "particle engulfment and pushing by solidifying interfaces (PEP)". Steady-state calculations were performed for different gravity levels and orientations with respect to the gravity vector The furnace configuration used in this analysis is the quench module insert (QMI-1) proposed for the Material Science Research Facility (MSRF) on board the International Space Station (ISS). The general model of binary alloy solidification was based on the finite element code FIDAP. At a low g level of 10(exp -4) g(sub o) (g(sub o) = 9.8 m/square s) maximum melt convection was obtained for an orientation of 90 deg. Calculations showed that even for this worst case orientation the dominant forces acting on the particle are the fundamental drag and interfacial forces.

Bune, Andris V.↗
NASA NTRS2001

Soot Surface Growth in Laminar Hydrocarbon/Air Diffusion Flames

The structure and soot surface growth properties of round laminar jet diffusion flames were studied experimentally. Measurements were made along the axes of ethylene-, propylene-propane- and acetylene-benzene-fueled flames burning in coflowing air at atmospheric pressure with the reactants at normal temperature. The measurements included soot structure, soot concentrations, soot temperatures, major gas species concentrations, some radial species (H, OH and O) concentrations, and gas velocities. These measurements yielded the local flame properties that are thought to affect soot surface growth as well as local soot surface growth rates. When present results were combined with similar earlier observations of acetylene-fueled laminar jet diffusion flames, the results suggested that soot surface growth involved decomposition of the original fuel to form acetylene and H, which were the main reactants for soot surface growth, and that the main effect of the parent fuel on soot surface growth involved its yield of acetylene and H for present test conditions. Thus, as the distance increased along the axes of the flames, soot formation (which was dominated by soot surface growth) began near the cool core of the flow once acetylene and H appeared together and ended near the flame sheet when acetylene disappeared. Species mainly responsible for soot oxidation - OH and O2 were present throughout the soot formation region so that soot surface growth and oxidation proceeded at the same time. Present measurements of soot surface growth rates (corrected for soot surface oxidation) in laminar jet diffusion flames were consistent with earlier measurements of soot surface growth rates in laminar premixed flames and exhibited good agreement with existing Hydrogen-Abstraction/Carbon-Addition (HACA) soot surface growth mechanisms in the literature with steric factors in these mechanisms having values on the order of unity, as anticipated.

El-Leathy, A. M.↗
NASA NTRS2003

Soot Surface Growth in Laminar Hydrocarbon/Air Diffusion Flames

The structure and soot surface growth properties of round laminar jet diffusion flames were studied experimentally. Measurements were made along the axes of ethylene-, propylene-propane- and acetylene-benzene-fueled flames burning in coflowing air at atmospheric pressure with the reactants at normal temperature. The measurements included soot structure, soot concentrations, soot temperatures, major gas species concentrations, some radial species (H, OH and 0) concentrations, and gas velocities. These measurements yielded the local flame properties that are thought to affect soot surface growth as well as local soot surface growth rates. When present results were combined with similar earlier observations of acetylene-fueled laminar jet diffusion flames, the results suggested that soot surface growth involved decomposition of the original fuel to form acetylene and H, which were the main reactants for soot surface growth, and that the main effect of the parent fuel on soot surface growth involved its yield of acetylene and H for present test conditions. Thus, as the distance increased along the axes of the flames, soot formation (which was dominated by soot surface growth) began near the cool core of the flow once acetylene and H appeared together and ended near the flame sheet when acetylene disappeared. Species mainly responsible for soot oxidation - OH and 02 were present throughout the soot formation region so that soot surface growth and oxidation proceeded at the same time. Present measurements of soot surface growth rates (corrected for soot surface oxidation) in laminar jet diffusion flames were consistent with earlier measurements of soot surface growth rates in laminar premixed flames and exhibited good agreement with existing Hydrogen-Abstraction/Carbon-Addition (HACA) soot surface growth mechanisms in the literature with steric factors in these mechanisms having values on the order of unity, as anticipated.

El-Leathy, A. M.↗
NASA NTRS1971

The three-dimensional steady radial expansion of a viscous gas from a sonic source into a vacuum.

The three-dimensional steady radial expansion of a viscous, heat-conducting, compressible fluid from a spherical sonic source into a vacuum is analyzed using the Navier-Stokes equations as a basis. It is assumed that the model fluid is a perfect gas having constant specific heats, a constant Prandtl number of order unity, and viscosity coefficients varying as a power of the absolute temperature. Limiting forms for the flow variable solutions are studied for the Reynolds number based on the sonic source conditions, going to infinity and the Newtonian parameter both fixed and going to zero. For the case of the viscosity-temperature exponent between .5 and 1, it is shown that the velocity as well as the pressure approach zero as the radial distance goes to infinity. The formulations of the distinct regions that span the domain extending from the sonic source to the vacuum are presented.

Bush, W. B.↗
NASA NTRS1982

Three dimensional flow field inside the passage of a low speed axial flow compressor rotor

Measurements of the subsonic flow in the rotor passage of a single stage axial flow compressor were made to study the nature of the flow field and to verify the existing numerical codes. The velocity and pressure fields were measured across the entire rotor passage at six axial locations and at five radial locations. A five-hole probe, rotating with the rotor, was used to measure the three components of velocity, the static and the total pressure. The experimental results are compared with the predictions from Katsanis and McNally's computer program. The agreement between the two is good for most of the cases.

Pouagare, M.↗
NASA NTRS1987

Velocity measurements in the plume of an arcjet engine

A nonintrusive technique has been used to conduct a radial survey in the flow field of an arcjet engine plume. The technique measures the Doppler shift of an optically thin line resulting from recombination and relaxation processes in the high Mach number stream, in order to determine flow velocities. Atom temperature can also be calculated from the same Doppler-broadened line widths, when these shifts are measured with a scanning Fabry-Perot spectrometer whose design is presented in detail.

Pivirotto, T. J.↗
NASA NTRS1982

Three dimensional mean velocity and turbulence characteristics in the annulus wall region of an axial flow compressor rotor passage

The experiment was performed using the rotating hot-wire technique within the rotor blade passage and the stationary hot-wire technique for the exitflow of the rotor blade passage. The measurements reveal the effect of rotation and subsequent flow interactions upon the rotor blade flowfield and wake development in the annulus-wall region. The flow near the rotor blade tips is found to be highly complex due to the interaction of the annulus-wall boundary layer, the blade boundary layers, the tip leakage flow, and the secondary flow. Within the blade passage, this interaction results in an appreciable radial inward flow as well as a defect in the mainstream velocity near the mid-passage. Turbulence levels within this region are very high. This indicates a considerable extent of flow mixing due to the viscous flow interactions. The size and strength of this loss core is found to grow with axial distance from the blade trailing edge. The nature of the rotor blade exit-flow was dominated by the wake development.

Davino, R.↗
NASA NTRS2004

A Rotary Flow Channel for Shear Stress Sensor Calibration

A proposed shear sensor calibrator consists of a rotating wheel with the sensor mounted tangential to the rim and positioned in close proximity to the rim. The shear stress generated by the flow at the sensor position is simply tau(sub omega) = (mu)r(omega)/h, where mu is the viscosity of the ambient gas, r the wheel radius, omega the angular velocity of the wheel, and h the width of the gap between the wheel rim and the sensor. With numerical values of mu = 31 (mu)Pa s (neon at room temperature), r = 0.5 m, omega = 754 /s (7200 rpm), and h = 50.8 m, a shear stress of tau(sub omega) = 231 Pa can be generated. An analysis based on one-dimensional flow, with the flow velocity having only an angular component as a function of the axial and radial coordinates, yields corrections to the above simple formula for the curvature of the wheel, flatness of the sensor, and finite width of the wheel. It is assumed that the sensor mount contains a trough (sidewalls) to render a velocity release boundary condition at the edges of the rim. The Taylor number under maximum flow conditions is found to be 62.3, sufficiently low to obviate flow instability. The fact that the parameters entering into the evaluation of the shear stress can be measured to high accuracy with well-defined uncertainties makes the proposed calibrator suitable for a physical standard for shear stress calibration.

Zuckerwar, Allan J.↗
NASA NTRS1998

Radial Distribution of Electron Spectra from High-Energy Ions

The average track model describes the response of physical and biological systems using radial dose distribution as the key physical descriptor. We report on an extension of this model to describe the average distribution of electron spectra as a function of radial distance from an ion. We present calculations of these spectra for ions of identical linear energy transfer (LET), but dissimilar charge and velocity to evaluate the differences in electron spectra from these ions. To illustrate the usefulness of the radial electron spectra for describing effects that are not described by electron dose, we consider the evaluation of the indirect events in microdosimetric distributions for ions. We show that folding our average electron spectra model with experimentally determined frequency distributions for photons or electrons provides a good representation of radial event spectra from high-energy ions in 0.5-2 micrometer sites.

Cucinotta, Francis A.↗
NASA NTRS1975

Turbulent flow between a rotating disk and a parallel wall

A scalar effective viscosity method is used to calculate the incompressible flow in the gap between two infinite, parallel smooth disks, one of them rotating and the other stationary. The flow is calculated for two values of the gap Reynolds number omega(s squared)/nu, namely 296 and 2852, where omega is the disk angular velocity, s the gap width, and nu the kinematic viscosity of the fluid; and over a range of radial Reynolds number omega(r squared)/nu from 0 to 10 million, where r is the radius from the axis of rotation. A numerical shooting technique is used to match the two boundary-layer flows arising on the disk and wall. Gradual transition is assumed for radial Reynolds numbers from 160,000 to 250,000. The results are in good agreement with Daily and Nece's measurements of velocity profiles and disk friction drag for enclosed rotating disks, and at sufficiently large radius the local skin friction approaches that of turbulent Couette flow.

Cooper, P.↗
NASA NTRS1989

Radial mixing of material in the asteroidal zone

The asteroid belt shows radial zoning of compositional structure. The most abundant types are successively S, C, and P types from the inner to the outer parts of the main belt, and D type in the Trojan clouds. This paper examines processes for producing this structure before, during, and after the accretion of asteroids. The initial structure is established by temperature and composition gradients in the turbulent solar nebula during the collapse of the presolar cloud. The radial scale of the zoning, comparable to the disk thickness, favors disk models with relatively low turbulent viscosity. Radial decay of solid bodies due to gas drag during settling to the central plane and planetesimal formation probably causes only a small degree of mixing, due to the systematic nature of drag-induced motions. The formation of Jupiter causes scattering of massive planetesimals from that planet's zone through the asteroid zone. The present random velocities of asteroids resulting from that stirring process are consistent with the radial scale of transitions between compositional types.

Ruzmaikina, T. V.↗
NASA NTRS1966

Flexible arms provide constant force for pressure switch calibration

In-place calibration of a pressure switch is provided by a system of radially oriented flexing arms which, when rotated at a known velocity, convert the centrifugal force of the arms to a linear force along the shaft. The linear force, when applied to a pressure switch diaphragm, can then be calculated.

Cain, D. E.↗
NASA NTRS1979

Evolution of a rotating flow in the vicinity of a surface

Evolution of a rotating flow in a body of fluid bounded by a stationary flat surface is discussed. The calculated results show that the radial pressure gradient is substantially reduced in the region close to the surface, so that letting that gradient be independent of distance from the surface would be expected to give only rough or qualitative estimates. However, the reduced rotation near the stationary surface is still large enough to cause an inflow near the surface and to set up a recirculation pattern. The concentration of vorticity by the radial inflow is not great enough to increase the tangential velocities near the center of rotation.

Deissler, R. G.↗
NASA NTRS1980

Performance of annular prediffuser-combuster systems

Results of an experimental investigation of the aerodynamic performance of several annular prediffuser-combustor systems are presented. Three curved wall, dump prediffusers of different length, area ratio, and turning angle were tested with and without a simulated combustor located downstream of the prediffuser. Performance was significantly influenced by the presence of the combustor. Pressure recovery and flow losses were determined as a function of prediffuser inlet velocity profile, flow extraction at the prediffuser inlet, axial and radial location of the combustor front end, and distribution of the flow in the combustor. Axial location of the combustor was found to be the most significant parameter influencing system performance.

Wagner, W. B.↗
NASA NTRS1981

Observations of large-scale motions of the Sun

Recent observations of large-scale mass motions on the Sun are discussed. The principal large-scale velocity flows are convection, rotation, meridional flow, and torsional and radial oscillations.

Labonte, B.↗