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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Energetic oxygen and sulfur ions in the Jovian magnetosphere

Observations of 1 to 20 MeV/nuc oxygen, sodium, and sulfur ions in the Jovian magnetosphere are reported. Measurements made by the cosmic ray subsystem on Voyager 1 and 2 were used to calculate abundances and energy spectra in the region from 5 to 20 Jovian radii. The phase space density of the oxygen ions calculated from the spectra has a positive radial gradient between 6 and 17 Jovian radii, indicating an inward diffusive flow. The diffusion coefficient upper limit at 9 Jovian radii is approximately 10 to the -5 power/s. This limit, combined with the analysis of Voyager plasma observations by Siscoe et al.1981, implies an upper limit to the mass loading rate near Io of approximately 10 to the 28th power ions/s. The energetic oxygen lifetime is within an order of magnitude of the strong pitch-angle diffusion lifetime in this region, with the largest total number of particles lost between 7.5 and 12.5 Jovian radii. It is shown that the losses are not due to geometric absorption by Io, absorption by dust grains, or energy loss in the plasma of the inner magnetosphere, and it is therefore postulated that the primary loss mechanism is pitch-angle scattering into the loss cone.

Gehrels, N.↗
NASA NTRS1996

Microgravity Turbulent Gas-Jet Diffusion Flames

A gas-jet diffusion flame is similar to the flame on a Bunsen burner, where a gaseous fuel (e.g., propane) flows from a nozzle into an oxygen-containing atmosphere (e.g., air). The difference is that a Bunsen burner allows for (partial) premixing of the fuel and the air, whereas a diffusion flame is not premixed and gets its oxygen (principally) by diffusion from the atmosphere around the flame. Simple gas-jet diffusion flames are often used for combustion studies because they embody the mechanisms operating in accidental fires and in practical combustion systems. However, most practical combustion is turbulent (i.e., with random flow vortices), which enhances the fuel/air mixing. These turbulent flames are not well understood because their random and transient nature complicates analysis. Normal gravity studies of turbulence in gas-jet diffusion flames can be impeded by buoyancy-induced instabilities. These gravitycaused instabilities, which are evident in the flickering of a candle flame in normal gravity, interfere with the study of turbulent gas-jet diffusion flames. By conducting experiments in microgravity, where buoyant instabilities are avoided, we at the NASA Lewis Research Center hope to improve our understanding of turbulent combustion. Ultimately, this could lead to improvements in combustor design, yielding higher efficiency and lower pollutant emissions. Gas-jet diffusion flames are often researched as model flames, because they embody mechanisms operating in both accidental fires and practical combustion systems (see the first figure). In normal gravity laboratory research, buoyant air flows, which are often negligible in practical situations, dominate the heat and mass transfer processes. Microgravity research studies, however, are not constrained by buoyant air flows, and new, unique information on the behavior of gas-jet diffusion flames has been obtained.

Source record↗
NASA NTRS1995

Coupled Monte Carlo Probability Density Function/ SPRAY/CFD Code Developed for Modeling Gas-Turbine Combustor Flows

The success of any solution methodology for studying gas-turbine combustor flows depends a great deal on how well it can model various complex, rate-controlling processes associated with turbulent transport, mixing, chemical kinetics, evaporation and spreading rates of the spray, convective and radiative heat transfer, and other phenomena. These phenomena often strongly interact with each other at disparate time and length scales. In particular, turbulence plays an important role in determining the rates of mass and heat transfer, chemical reactions, and evaporation in many practical combustion devices. Turbulence manifests its influence in a diffusion flame in several forms depending on how turbulence interacts with various flame scales. These forms range from the so-called wrinkled, or stretched, flamelets regime, to the distributed combustion regime. Conventional turbulence closure models have difficulty in treating highly nonlinear reaction rates. A solution procedure based on the joint composition probability density function (PDF) approach holds the promise of modeling various important combustion phenomena relevant to practical combustion devices such as extinction, blowoff limits, and emissions predictions because it can handle the nonlinear chemical reaction rates without any approximation. In this approach, mean and turbulence gas-phase velocity fields are determined from a standard turbulence model; the joint composition field of species and enthalpy are determined from the solution of a modeled PDF transport equation; and a Lagrangian-based dilute spray model is used for the liquid-phase representation with appropriate consideration of the exchanges of mass, momentum, and energy between the two phases. The PDF transport equation is solved by a Monte Carlo method, and existing state-of-the-art numerical representations are used to solve the mean gasphase velocity and turbulence fields together with the liquid-phase equations. The joint composition PDF approach was extended in our previous work to the study of compressible reacting flows. The application of this method to several supersonic diffusion flames associated with scramjet combustor flow fields provided favorable comparisons with the available experimental data. A further extension of this approach to spray flames, three-dimensional computations, and parallel computing was reported in a recent paper. The recently developed PDF/SPRAY/computational fluid dynamics (CFD) module combines the novelty of the joint composition PDF approach with the ability to run on parallel architectures. This algorithm was implemented on the NASA Lewis Research Center's Cray T3D, a massively parallel computer with an aggregate of 64 processor elements. The calculation procedure was applied to predict the flow properties of both open and confined swirl-stabilized spray flames.

Source record↗
NASA NTRS1990

On the origin of metal homogeneities in globular clusters

Various transport processes which may have affected the chemical homogeneity in protocluster clouds are examined. It is shown that the characteristic diffusion time scale associated with collisions between grains and gas atoms is considerably longer than that on which star formation is expected to occur. Collisions between large grains and gas atoms lead to mass segregation and metallicity gradients on a time scale comparable to the crossing time of the clusters in the Galaxy. One possible mechanism for inducing and maintaining chemical homogeneity is turbulent diffusion in the clouds. The mixing time scale required in this case is comparable to several internal dynamical time scales, longer than the evolutionary time scale of the most massive stars, and shorter than the Galactic orbital time scale of the clouds. Thus, metals in presently observed stars probably did not originate from upper main-sequence stars of a coeval generation.

Murray, Stephen D.↗
NASA NTRS1972

A study of graphite ablation in combined convective and radiative heating.

Comparison of graphite ablation experiment results in the diffusion-controlled oxidation and sublimation regimes with results of an equilibrium chemistry, film coefficient ablation analysis. Mass transfer and energy transfer effects are considered. Tests were conducted in an arcjet facility at convective heating rates of 600 to 800 W/sq cm, radiative heating rates up to 2900 W/sq cm, with test specimen surface pressures of 0.06, 0.1, and 0.3 atm in an air stream. The experimental and analytical mass loss and surface temperature results agreed well when the carbon vapor thermodynamic properties from the JANAF tables are used in the analysis.

Wakefield, R. M.↗
NASA NTRS1978

Cold-air performance of a tip turbine designed to drive a lift fan

Performance was obtained over a range of speeds and pressure ratios for a 0.4 linear scale version of the LF460 lift fan turbine with the rotor radial tip clearance reduced to about 2.5 percent of the rotor blade height. These tests covered a range of speeds from 60 to 140 percent of design equivalent speed and a range of scroll inlet total to diffuser exit static pressure ratios from 2.6 to 4.2. Results are presented in terms of equivalent mass flow, equivalent torque, equivalent specific work, and efficiency.

Haas, J. E.↗
NASA NTRS1979

X-ray emission from an Ap star /Phi Herculis/ and a late B star /Pi Ceti/

Using the HEAO 1 soft X-ray sky survey, a search was conducted for X-ray emission from 18 stars in the spectral range B5-A7. The detection of 0.25 keV X-ray sources consistent with the positions of Pi Ceti, a normal B7 V star, and Phi Herculis, a classic Ap star was reported. The detection of these stars argues for large mass motions in the upper layers of stars in this spectral range, and argues against radiative diffusion as the source of abundance anomalies in Ap stars.

Cash, W.↗
NASA NTRS1980

Electroepitaxy of multicomponent systems - Ternary and quarternary compounds

A theoretical model is presented which accounts for the electroepitaxial growth kinetics and composition of multicomponent compounds in terms of mass transport in the liquid and phase diagram relationships. The mass transport in the interface is dominated by electromigration in the absence of convection and by diffusion in the presence of convection. The composition of the solid is controlled by the Peltier effect at the growth interface and by the diffusion and mobility constants of the solute components and the growth velocity (current density). Thus, for a given solution composition, the composition of the solid can be varied by varying the current density. For a given current density the composition remains constant even in the case of relatively thick epitaxial layers. All aspects of the model were found to be in good agreement with the growth and composition characteristics of Ga/x-1/Al/x/As layers.

Bryskiewicz, T.↗
NASA NTRS1987

Recent developments in indium phosphide space solar cell research

Recent developments and progress in indium phosphide solar cell research for space application are reviewed. Indium phosphide homojunction cells were fabricated in both the n+p and p+n configurations with total area efficiencies of 17.9 and 15.9% (air mass 0 and 25 C) respectively. Organometallic chemical vapor deposition, liquid phase epitaxy, ion implantation and diffusion techniques were employed in InP cell fabrication. A theoretical model of a radiation tolerant, high efficiency homojunction cell was developed. A realistically attainable AMO efficiency of 20.5% was calculated using this model with emitter and base doping of 6 x 10 to the 17th power and 5 x 10 the the 16th power/cu cm respectively. Cells of both configurations were irradiated with 1 MeV electrons and 37 MeV protons. For both proton and electron irradiation, the n+p cells are more radiation resistant at higher fluences than the p+n cells. The first flight module of four InP cells was assembled for the Living Plume Shield III satellite.

Brinker, David J.↗
NASA NTRS1986

On the direct and dissociative excitation of the O(3s 3S0) state by electron impact on atomic and molecular oxygen

The ratio of the cross sections for the direct and dissociative excitation of the OI(3s 3S0-2p 3P; 1304 A wavelength) transition, sigma A/sigma D, are accurately determined, and the sigma A/sigma D ratio is directly normalized to the ratio of the O(+) and O2(+) ionization cross sections using a high-density diffuse gas source, an electrostatically focused electron gun, a vacuum-ultraviolet monochromater, and a quadrupole mass spectrometer for simultaneous optical and composition measurements. Using revised sigma A(1304 A) values calculated with new calibration standards, the shape of the cross section for the excitation of the O(3s 3S0) state agrees well with previous results, though the absolute magnitude of sigma A(1304 A) is smaller than the results of Stone and Zipf (1974) by a factor of 2.8. The revised cross sections agree well with recent quantum calculations when cascade excitation of the 3s 3S0 state is taken into account.

Zipf, E. C.↗
NASA NTRS1987

Gamma-ray constraints on Na-22 yields in nova explosions

The longitudinal distribution of diffuse 1.275 MeV emission produced by the decay of interstellar Na-22 generated by a limited class of energetic novae-accreting ONeMg white dwarfs is modeled. The probability distributions for the locations of disk novae are derived as functions of Galactocentric cylindrical coordinates. The occurrence rate for novae of all classes in the Galactic disk is about 30/yr. An occurrence rate of about 16/yr is found for spheroid novae of all classes. By comparing these simulation results with HEAO 3 upper limits on diffuse 1.275 MeV emission, upper limits of (3-5.6) x 10 to the -7th solar mass are determined for the mean Na-22 yield for energetic novae generated by accreting ONeMg white dwarfs. These Na-22 limits constrain future models of explosive nucleosynthesis in energetic nova explosions.

Higdon, J. C.↗
NASA NTRS1987

Recent developments in indium phosphide space solar cell research

Recent developments and progress in indium phosphide solar cell research for space application are reviewed. Indium phosphide homojunction cells were fabricated in both the n + p and p + n configurations with total area efficiencies of 17.9 and 15.9 percent (air mass 0 and 25 C) respectively. Organometallic chemical vapor deposition, liquid phase epitaxy, ion implantation and diffusion techniques were employed in InP cell fabrication. A theoretical model of a radiation tolerant, high efficiency homojunction cell was developed. A realistically attainable AM0 efficiency of 20.5 percent was calculated using this model with emitter and base doping of 6 x 10 to the 17th power and 5 x 10 to the 16th power/cu cm, respectively. Cells of both configurations were irradiated with 1 MeV electrons and 37 MeV protons. For both proton and electron irradiation, the n + p cells are more radiation resistant at higher fluences than the p + n cells. The first flight module of four InP cells was assembled for the Living Plume Shield III satellite.

Brinker, David J.↗
NASA NTRS1993

Segmented multigrid domain decomposition solutions for three dimensional viscous recirculating flows

A segmented multigrid domain decomposition strategy is combined with a pressure-based form of flux-vector discretization for 3D incompressible and compressible viscous flow applications. A pressure-based form of flux-vector splitting is applied to the Navier-Stokes (NS) equations, which are represented by an implicit lowest-order reduced NS system and a purely diffusive higher-order deferred corrector. A trapezoidal or boxlike form of discretization insures that all mass conservation properties are satisfied at interfacial and outflow boundaries, even for this primitive-variable nonstaggered grid computation. Improvements in gridding strategy are presented by allowing for disjoint subdomains that provide optimal resolution of disparate flow features.

Srinivasan, Kumar↗
NASA NTRS1995

Seasonal variability of light availability and utilization in the Sargasso Sea

A 2 year time series of optical, biogeochemical, and physical parameters, taken near the island of Bermuda, is used to evaluate the sources of temporal variability in light avaliability and utilization in the Sargasso Sea. Integrated assessments of light availability are made by examining the depth of constant percent incident photosynthetically available radiation (% PAR) isolumes. To first order, changes in the depth %PAR isolumes were caused by physical processes: deep convection mixing in the winter which led to the spring bloom and concurrent shallowing of %PAR depths and the occurrence of anomalous thermohaline water masses during the summer and fall seasons. Spectral light availability variations are assessed using determinations of diffuse attenuation coefficient spectra which illustrates a significant seasonal cycle in colored detrital particulate and/or dissolved materials that is unrelated to changes in chlorophyll pigment concentrations. Temporal variations in the photosynthetic light utilization index Psi are used to assess vertically intergrated light utilization variations. Values of Psi are highly variable and show no apparent seasonal pattern which indicates that Psi is not simply a 'biogeochemical constant.' Determinations of in situ primary production rates and daily mean PAR fluxes are used to diagnose the relative role of light limitation in determining vertically integrated rates of primary production integral PP. The mean depth of the light-saturated zone (the vertical region where the daily mean PAR flux was greater than or equal to the saturation irradiance) is only approximately 40 m, although more than one half of interal PP occurred within this zone. Production model results illustrate that accurate predictions of integral PP are dependent upon rates of light-saturated production rather than upon indices of light limitation. It seems unlikely that significant improvements in simple primary production models will come from the partitioning of the Earth's seas into biogeochemical provinces.

Siegel, David A.↗
NASA NTRS2018

Quantitative Analysis of Planar Laser-Induced Fluorescence Measurements in a Hypersonic Boundary Layer

Several quantitative measurements extracted from nitric oxide (NO) planar laser-induced fluorescence (PLIF) data obtained in a hypersonic boundary layer are reported: (a) off-body NO mole fraction; (b) surface heat flux; and (c) near-wall static temperature. The experimental data was obtained at NASA Langley Research Center’s 31 in. Mach 10 air tunnel. NO was seeded into the flow through a spanwise slot on the surface of the 10 degree half-angle wedge model. An ultraviolet planar laser sheet was positioned perpendicular to the wedge surface, downstream of the seeding slot, to excite six fluorescence transitions. A method for extracting the relative NO mole fraction, based on spatial variations of the J”= 0.5 PLIF signal, is presented. Combined with the principle of mass conservation, the absolute NO mole fraction is determined. These measurements were used to assess CFD diffusion modelling, correct previously reported PLIF thermometry results, and develop methods for NO-PLIF heat transfer measurements.

McDougall, Connor C.↗
NASA NTRSDate not supplied

Numerical Investigation of Film Coefficient Engineering Methodology for Dissociated, Chemically Reacting Boundary Layers

Aerothermal analysis of spacecraft planetary entry is heavily dependent on heritage engineering models. The film coefficient heat transfer model examined in this paper estimates the convective heating to the vehicle for a laminar, dissociated, chemically reacting boundary layer for an Earth atmosphere. This model requires information about the vehicle and flow field for a given trajectory point and estimates a proportional relationship between enthalpy potential and convective heat flux. In practice it is the aerothermal engineer who must decide which assumptions are appropriate for their application. This work looks at numerous CFD simulations for an arbitrary, axisymmetric flight vehicle to analyze the relative importance of both the mass and energy constraints imposed at the wall boundary, as well as the effect of various diffusion models. The sensitivity of the engineering model is assessed based on the impact of the CFD assumptions as an effort to make it available to design engineers across industry.

numerical boundary layer↗
NASA NTRS2023

Numerical Investigation of Film Coefficient Approximation for Chemically Reacting Boundary-Layer Flows

Aerothermal analysis of spacecraft planetary entry is heavily dependent on heritage engineering models. The film coefficient heat transfer model examined in this paper estimates the convective heating to the vehicle for a laminar, dissociated, chemically reacting boundary layer for an Earth atmosphere. This model requires information about the vehicle and flowfield for a given trajectory point and estimates a proportional relationship between enthalpy potential and convective heat flux. In practice it is the aerothermal engineer who must decide which assumptions are appropriate for his/her application. This work looks at numerous CFD simulations for an arbitrary, axisymmetric flight vehicle to analyze the relative importance of both the mass and energy constraints imposed at the wall boundary, as well as the effect of various diffusion models. Within the subset of tested energy boundary conditions, it is found that the most desirable energy boundary condition is the radiative equilibrium boundary condition, which permits conservative estimates of convective heat flux, but also generates flowfield-dependent spatial thermal distributions along the surface. Other key findings are presented in an effort to make the film coefficient engineering model readily available to design engineers across industry.

Film coefficient↗
NASA NTRS1977

Soot and hydrocarbon formation in a turbulent diffusion flame

Formation and emission of soot and polycyclic aromatic hydrocarbons (PCAH) from a turbulent continuous flow combustor have been studied. Measurements included mass concentration of both soot and PCAH, composition of individual PCAH, and size distribution of soot particles, as a function of mixing intensity, fuel equivalence ratio and type of fuel (kerosene or benzene). Both soot and PCAH concentrations reach maxima early in the flame, after which PCAH decays rapidly and soot decays much slower. The maximum PCAH concentration always preceded that of soot in agreement with the concept that certain PCAH may serve as intermediates in soot formation. An approximate calculation based on the assumptions of local equilibrium with respect to soot formation and a Gaussian distribution of air-fuel mixedness gave satisfactory correlations of the data on soot formation at the higher cold gas velocity. At the lower velocity, the amount of soot and PCAH formed was drastically increased and strongly dependent on fuel atomization.

Prado, G. P.↗