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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Mixing in Low Reynolds Number Reacting Impinging Jets in Crossflow

Previous efforts to model uranyl fluoride formation in an impinging jet gas reactor underpredicted spatial mixing and overpredicted chemical conversion into particulates. The previous fluid dynamics model was based on the solution of the Reynolds Averaged Navier Stokes equations. After simulating fluid dynamics, aerosol dynamics were superimposed onto CFD-simulated gas reactant species concentrations. The current work explores the influence of complex unsteady flow features on the overall flow physics and chemistry for a low Reynolds number, opposed flow, impinging jet gas reactor where there is a low Reynolds number cross flow. The objective of this study was to assess the impact of model formulation on scalar mixing and transport. Here, transient flow simulations were performed using Scale Resolving Simulations. Large-Eddy Simulations with the dynamic Smagorinsky turbulence model were performed along with simulations which directly resolved the flow. Average and root-mean-square (RMS) velocities and species concentrations were computed along with modeled and resolved turbulence kinetic energy (TKE), modeled turbulence dissipation, and modeled turbulent viscosity. Lagrangian flow tracers were also used to quantify species concentrations along path lines emanating from the jet tips. Transient simulation data were compared to results from RANS simulations using the k-ω shear stress transport (SST) model and Reynolds Stress Model (RSM). Transient simulations showed spatial mixing patterns which were more consistent with experimental data and helped elucidate the process of particle formation observed in experiments.

42 ENGINEERING↗
NASA NTRS1972

X-ray study of solar plage regions and a small flare.

The O VII and Ne IX resonance line and 5 keV continuum emission of a small solar flare are interpreted on the basis of a model in which the emission measure of the region is an exponentially decreasing function of temperature. Good agreement with all three sets of data is obtained - a result not possible on the basis of an isothermal approximation. The change in the emission of the flare over a two minute interval appears to be consistent with a simple cooling of the region. Computation of the contribution function versus temperature for each emission indicates that each predominantly comes from a physically separate volume within the feature. The emission measure distribution for the flare is distinctly flatter than that of five plage regions which tend to have similar slopes and which are in turn flatter than the general corona.

Acton, L. W.↗
NASA NTRS1973

Ferrite logic reliability study

Development and use of digital circuits called all-magnetic logic are reported. In these circuits the magnetic elements and their windings comprise the active circuit devices in the logic portion of a system. The ferrite logic device belongs to the all-magnetic class of logic circuits. The FLO device is novel in that it makes use of a dual or bimaterial ferrite composition in one physical ceramic body. This bimaterial feature, coupled with its potential for relatively high speed operation, makes it attractive for high reliability applications. (Maximum speed of operation approximately 50 kHz.)

Baer, J. A.↗
NASA NTRS1975

The auditory neural network in man

The principles of anatomy and physiology necessary for understanding brain wave recordings made from the scalp of normal people are briefly discussed. Brain waves evoked by sounds are described and certain of their features are related to the physical aspects of the stimulus and to the psychological state of the listener. The position is taken that data obtained through scalp probes can reveal a large amount of detail about brain functioning and that analysis of such records enable detection of the response of the nervous system to an acoustic message at the moment of its inception and to the progress of the message through the brain. Brain events responsible for distinguishing between similar signals and making decisions about them appear to generate characteristic and identifiable electrical waves. Some theoretical speculation about these data are introduced with the aim of generating a more heuristic model of the functioning brain.

Galambos, R.↗
NASA NTRS1975

The auditory neural network in man

The principles of anatomy and physiology necessary for understanding brain wave recordings made from the scalp are briefly discussed. Brain waves evoked by sounds are then described and certain of their features are related to the physical aspects of the stimulus and the psychological state of the listener. It is proposed that data obtained through probes located outside the head can reveal a large amount of detail about brain activity. It is argued that analysis of such records enables one to detect the response of the nervous system to an acoustic message at the moment of its inception at the ear, and to follow the progress of the acoustic message up through the various brain levels as progressively more complex operations are performed upon it. Even those brain events responsible for the highest level of signal processing - distinguishing between similar signals and making decisions about them - seem to generate characteristic and identifiable electrical waves.

Galambos, R.↗
NASA NTRS1977

High resolution 10 mu spectrometry at different planetary latitudes. A practical Hadamard transform spectrometer for astronomical application

Infrared observations at different latitudes were studied in order to obtain spectra in the 10 micrometers region to understand differences in chemical composition or physical structure of the optical features. In order to receive such spectra of a rotating planet, simultaneous observations at different latitudes were made. A Hadamard transform spectrometer with 15 entrance slits was used to obtain 15 simultaneous spectra, at a resolution of 0.01 micrometers. The spectral band covered contained 255 spectral elements.

Tai, M. H.↗
NASA NTRS1981

Prediction of blade-vortex interaction noise from measured blade pressure

The impulsive nature of noise due to the interaction of a rotor blade with a tip vortex is studied. The time signature of this noise is calculated theoretically based on the measured blade surface pressure fluctuation of an operational load survey rotor in slow descending flight and is compared with the simultaneous microphone measurement. Particularly, the physical understanding of the characteristic features of a waveform is extensively studied in order to understand the generating mechanism and to identify the important parameters. The interaction trajectory of a tip vortex on an acoustic planform is shown to be a very important parameter for the impulsive shape of the noise. The unsteady nature of the pressure distribution at the very leading edge is also important to the pulse shape. The theoretical model using noncompact liner acoustics predicts the general shape of interaction impulse pretty well except for peak amplitude which requires more continuous information along the span at the leading edge.

Nakamura, Y.↗
NASA NTRS1981

Prediction of blade vortex interaction noise from measured blade pressure

The impulsive nature of noise due to the interaction of a rotor blade with a tip vortex is studied. The time signature of this noise is calculated theoretically based on the measured blade surface pressure fluctuation of an operational load survey rotor in slow descending flight and is compared with the simultaneous microphone measurement. Particularly, the physical understanding of the characteristic features of a waveform is extensively studied in order to understand the generating mechanism and to identify the important parameters. The interaction trajectory of a tip vortex on an acoustic planform is shown to be a very important parameter for the impulsive shape of the noise. The unsteady nature of the pressure distribution at the very leading edge is also important to the pulse shape. The theoretical model using noncompact linear acoustics predicts the general shape of interaction impulse pretty well except for peak amplitude which requires more continuous pressure information along the span at the leading edge.

Nakamura, Y.↗
NASA NTRS1982

Visible and near-IR spectral reflectance of geologically important materials: A short review

Examples of reflectance spectra are presented and discussed for various mineral groups including pyroxenes, olivene, phylosilicates, amphiboles, feldspars, oxides and hydroxides, carbonates, and mixtures of minerals. The physical sources of some spectral features are also reviewed such as charge transfer and conduction bands, crystal field absorptions, and vibrational absorptions.

Singer, R. B.↗
NASA NTRS1986

The poleward edge of the mid-latitude trough - Its formation, orientation and dynamics

Data from the Advanced Ionospheric Sounder (AIS) deployed at Halley, Antarctica (76-deg S, 27-deg W; L = 4.2) and the Dynamics Explorer-2 spacecraft (DE-2) are used to investigate several aspects of the formation processes and dynamics of the poleward edge of the midlatitude electron density trough. These include a study of the flux and energy of charged particles precipitating into the F-region as a function of Magnetic Local Time. It is found that local energetic electron precipitation is a major source of ionization of the poleward edge in the evening sector, but only after magnetic midnight transport processes become more important. Occasionally a significant increase in the flux of conjugate photoelectrons is colocated with the poleward edge of the trough in the morning sector. The combination of AIS and DE-2 data has allowed identification of significant longitudinal structure on the poleward edge of the trough that may be the result of substorm activity. It is found that the orientation of the poleward edge of the trough and the locus of the plasmapause predicted from the 'tear-drop' model vary in rather a similar manner with local time, though no close physical link between the two features is inferred from this coincidence.

Rodger, A. S.↗
NASA NTRS1989

CFD for hypersonic airbreathing aircraft

A general discussion is given on the use of advanced computational fluid dynamics (CFD) in analyzing the hypersonic flow field around an airbreathing aircraft. Unique features of the hypersonic flow physics are presented and an assessment is given of the current algorithms in terms of their capability to model hypersonic flows. Several examples of advanced CFD applications are then presented.

Kumar, Ajay↗
NASA NTRS1994

Live from Antarctica: the Coldest, Windiest Place on Earth

In this first part of a four part 'Passport to Knowledge Special', hosted by Camille Jennings from Maryland Public Television, children from Maryland and Texas schools had the opportunity to directly interact with and ask questions of scientists and researchers in Antarctica live. The physical characteristics of Antarctica are featured, along with their effects on the human and microbiological organisms living in the region. The reasons behind the clothing worn in the Antarctic and the importance of the meteorological station are featured. Interviews with Professor Ian Dolziel (U of Texas) and Lt. commander John Joseph, NSFA (the head of the Navy Meteorology Center) occur with the school children, along with actual video footage of the surrounding geological features and geography. The 'Weatherops' is located at McMurdo Station, Antarctica.

Source record↗
NASA NTRS2006

Evidence for a Binary Companion to the Enigmatic Compact Central Object 1E 1207.4-5209

Located in the supernova remnant G296.5+10.0, 1E 1207.4-5209 is a 0.424 s period X-ray pulsar that exhibits strong absorption lines in its energy spectrum. The physical origin of the spectral features in 1E 1207.4-5209 and more generally, the absence of similar features in other radio-quiet neutron stars remains a mystery. Another, possibly related, anomalous property of 1E 1207.4-5209 is its non-monotonic spin frequency evolution. Zavlin, Pavlov & Sanwal(2004) proposed that the irregular spin-down was caused by either (i) frequent, recurrent glitches, (ii) the presence of a fall-back disk or (iii) a binary companion. Here, we report on a sequence of seven XMM-Newton observations of 1E 1207.4-5209 performed during a 40 day window between 2005 June 22 and July 3 1. Due to unanticipated phase noise, we identified three statistically-acceptable phase-coherent timing solutions with frequency time derivatives of +0.9, -2.6, and +1.6 x 10-12 Hz/s (listed in descending order of significance). We concluded that the local frequency derivative during our XMM-Newton observing campaign differs from the long-term spin-down rate by more than an order of magnitude. This measurement strongly supports the binary interpretation for the observed spin irregularities in 1E 1207.4-5209. We identified a family of orbital solutions that are consistent with our phase-connected solution as well as all archival data. We will discuss possible orbital solutions, prospects for constraining binary parameters with future observations, and consequences for the nature of 1E 1207.4-5209.

Woods, P. M.↗
NASA NTRS2008

Mergers of Non-spinning Black-hole Binaries: Gravitational Radiation Characteristics

We present a detailed descriptive analysis of the gravitational radiation from black-hole binary mergers of non-spinning black holes, based on numerical simulations of systems varying from equal-mass to a 6:1 mass ratio. Our primary goal is to present relatively complete information about the waveforms, including all the leading multipolar components, to interested researchers. In our analysis, we pursue the simplest physical description of the dominant features in the radiation, providing an interpretation of the waveforms in terms of an implicit rotating source. This interpretation applies uniformly to the full wavetrain, from inspiral through ringdown. We emphasize strong relationships among the l = m modes that persist through the full wavetrain. Exploring the structure of the waveforms in more detail, we conduct detailed analytic fitting of the late-time frequency evolution, identifying a key quantitative feature shared by the l = m modes among all mass-ratios. We identify relationships, with a simple interpretation in terms of the implicit rotating source, among the evolution of frequency and amplitude, which hold for the late-time radiation. These detailed relationships provide sufficient information about the late-time radiation to yield a predictive model for the late-time waveforms, an alternative to the common practice of modeling by a sum of quasinormal mode overtones. We demonstrate an application of this in a new effective-one-body-based analytic waveform model.

Baker, John G.↗
NASA NTRS2012

Simulations of Magnetic Reconnection - Kinetic Mechanisms Underlying the Fluid Description of Ions

Because of its ability to transfer the energy stored in magnetic field together with the breaking of the flux freezing constraint, magnetic reconnection is considered as one of the most important phenomena in plasma physics. When it happens in a collision less environment such as the terrestrial magnetosphere, it should a priori be modelled with in the framework of kinetic physics. The evidence of kinetic features has incidentally for a long time, been shown by researchers with the help of both numerical simulations and satellite observations. However, most of our understanding of the process comes from the more intuitive fluid interpretation with simple closure hypothesis which do not include kinetic effects. To what extent are these two separate descriptions of the same phenomenon related? What is the role of kinetic effects in the averaged/fluid dynamics of reconnection? This thesis addresses these questions for the proton population in the particular case of anti parallel merging with the help of 2D Hybrid simulations. We show that one can not assume, as is usually done, that the acceleration of the proton flow is only due to the Laplace force. Our results show, for symmetric and asymmetric connection, the importance of the pressure force, opposed to the electric one on the separatrices, in the decoupling region. In the symmetric case, we emphasize the kinetic origin of this force by analyzing the proton distribution functions and explain their structure by studying the underlying particle dynamics. Protons, as individual particles, are shown to bounce in the electric potential well created by the Hall effect. The spatial divergence of this well results in a mixing in phase space responsible for the observed structure of the pressure tensor. A detailed energy budget analysis confirms the role of the pressure force for the acceleration; but, contrary to what is sometimes assumed, it also reveals that the major part of the incoming Poynting flux is transferred to the thermal energy flux rather than to the convective kinetic energy flux, although the latter is generally supposed dominant. In the symmetric case, we propose the pressure tensor to be an additional proxy of the ion decoupling region in satellite data and verify this suggestion by studying a reconnection event encountered by the Cluster spacecrafts. Finally, the last part of this thesis is devoted to the study of the kinetic structure of asymmetric tangential current sheets where connection can develop. This theoretical part consists in finding a steady state solution to the Vlasov-Maxwell system for the protons in such a configuration. We present the theory and its first confrontation to numerical tests.

Aunai, icolas↗
NASA NTRSDate not supplied

TPSAS-NF1676L-30686-DND

Langley Research Center's Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) model began model formulation and development in 2004, and is running in real-time at the LaRC/DAAC since April 2011. Distinguishing features: real-time physics-based, global model; real-time inclusion of SEP radiation; and real-time solar-magnetospheric effects on radiation.

Amanda Fritz↗
NASA NTRS2021

Continuum, cyclotron line, and absorption variability in the high-mass X-ray binary Vela X-1

Because of its complex clumpy wind, prominent cyclotron resonant scattering features, intrinsic variability, and convenient physical parameters (close distance, high inclination, and small orbital separation), which facilitate the observation and analysis of the system, Vela X-1 is one of the key systems for understanding accretion processes in high-mass X-ray binaries on all scales. We revisit Vela X-1 with two new observations taken with NuSTAR at orbital phases ∼0.68–0.78 and ∼0.36–0.52, which show a plethora of variability and allow us to study the accretion geometry and stellar wind properties of the system. We follow the evolution of spectral parameters down to the pulse period timescale using a partially covered power law continuum with a Fermi-Dirac cutoff to model the continuum and local absorption. We are able to confirm anti-correlations between the photon index and the luminosity and, for low fluxes, between the folding energy and the luminosity, implying a change of properties in the Comptonising plasma. We were not able to confirm a previously seen correlation between the cyclotron line energy and the luminosity of the source in the overall observation, but we observed a drop in the cyclotron line energy following a strong flare. We see strong variability in absorption between the two observations and within one observation (for the ∼0.36–0.52 orbital phases) that can be explained by the presence of a large-scale structure, such as accretion and photoionisation wakes in the system, and our variable line of sight through this structure.

C. M. Diez↗
NASA NTRS1982

Shuttle imaging radar experiment

The Shuttle imaging radar (SIR-A) acquired images of a variety of the earth's geologic areas covering about 10 million square kilometers. Structural and geomorphic features such as faults, folds, outcrops, and dunes are clearly visible in both tropical and arid regions. The combination of SIR-A and Seasat images provides additional information about the surface physical properties: topography and roughness. Ocean features were also observed, including large internal waves in the Andaman Sea.

Elachi, C.↗