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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
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↗
DOE OSTI2019

Geodesic modes driven by untrapped resonances of NB energetic ions in tokamaks

Geodesic modes are typically excited by a minor concentration of energetic ions, but unstable mode frequencies are substantially different from Geodesic Acoustic Modes (GAMs) and are named EGAM (Energetic particle GAM). The EGAM instability driven by Neutral Beam Injection (NBI) has been observed in DIII-D tokamak experiments. The problem of the geodesic mode instability is analytically studied using a full drift kinetic equation. To analyze the instability condition, an ionization NBI location is assumed to be on the high field side of tokamaks. Here, a minority NBI ion distribution is modeled by an energetic ion tail in the untrapped-passing region that remains between a magnetic axis and the trapped NBI boundary. The EGAM instability condition is defined by the parallel NBI ion velocity v | | ≈ ( 1.2 – 1.5 ) ω R 0 q 0 that has to be above the effective EGAM phase velocity. In this case, the EGAM frequency is ≈ 50 % below the standard stable GAM frequency, which is reduced by a small concentration of energetic NBI ions. Qualitative comparison of the developed geodesic mode theory with NBI heating experiments in the midregion of the tokamak plasma is discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Magnetized laser–plasma interactions in high-energy-density systems: Parallel propagation

In this study, we investigate parametric processes in magnetized plasmas, driven by a large-amplitude pump light wave. Our focus is on laser–plasma interactions relevant to high-energy-density (HED) systems, such as the National Ignition Facility and the Sandia MagLIF concept. We present a self-contained derivation of a “parametric” dispersion relation for magnetized three-wave interactions, meaning the pump wave is included in the equilibrium, similar to the unmagnetized work of Drake et al., Phys. Fluids 17, 778 (1974). For this, we use a multi-species plasma fluid model and Maxwell's equations. The application of an external B field causes right- and left-polarized light waves to propagate with differing phase velocities. This leads to Faraday rotation of the polarization, which can be significant in HED conditions. Phase-matching and linear wave dispersion relations show that Raman and Brillouin scattering have modified spectra due to the background B field, though this effect is usually small in systems of current practical interest. We study a scattering process we call stimulated whistler scattering, where a light wave decays to an electromagnetic whistler wave (ω≲ω ce ) and a Langmuir wave. This only occurs in the presence of an external B field, which is required for the whistler wave to exist.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1999

Effects of body orientation and rotation axis on pitch visual-vestibular interaction

Spatial transformations of the vestibular-optokinetic system must account for changes in head position with respect to gravity in order to produce compensatory oculomotor responses. The purpose of this experiment was to study the influence of gravity on the vestibulo-ocular reflex (VOR) in darkness and on visual-vestibular interaction in the pitch plane in human subjects using two different comparisons: (1) Earth-horizontal axis (EHA) rotation about an upright versus a supine body orientation, and (2) Earth-horizontal versus Earth-vertical (EVA) rotation axes. Visual-vestibular responses (VVR) were evaluated by measuring the slow phase velocity of nystagmus induced during sinusoidal motion of the body in the pitch plane (at 0.2 Hz and 0.8 Hz) combined with a constant-velocity vertical optokinetic stimulation (at +/- 36 degrees/s). The results showed no significant effect on the gain or phase of the VOR in darkness or on the VVR responses at 0.8 Hz between EHA upright and EHA supine body orientations. However, there was a downward shift in the VOR bias in darkness in the supine orientation. There were systematic changes in VOR and VVR between EHA and EVA for 0.2 Hz, including a reduced modulation gain, increased phase lead, and decreased bias during EVA rotation. The same trend was also observed at 0.8 Hz, but at a lesser extent, presumably due to the effects of eccentric rotation in our EVA condition and/or to the different canal input across frequencies. The change in the bias at 0.2 Hz between rotation in darkness and rotation with an optokinetic stimulus was greater than the optokinetic responses without rotation. During EHA, changes in head position relative to gravity preserve graviceptor input to the VVR regardless of body orientation. However, the modifications in VVR gain and phase when the rotation axis is aligned with gravity indicate that this graviceptive information is important for providing compensatory eye movements during visual-vestibular interaction in the pitch plane.

Non-NASA Center↗
NASA NTRS1975

Further study of the atmospheric gravity waves over the eastern seaboard on 18 March 1969

Washington, D.C., microbarograph records for Mar. 18, 1969 reveal gravity-wave-associated pressure oscillations which appear to be directly related to upper tropospheric wave structure observed at the same time with a Wallops Island 10-cm wavelength radar. The consistency between the two sets of data provides observational support for the hypothesis that shear instability in the upper tropospheric flow is the mechanism responsible for the generation of such waves. The comparison presented suggests that microbarograph arrays might be useful adjuncts to future radar studies of upper tropospheric wave dynamics, supplying such wave parameters as phase velocity and wavelength in favorable cases. The radar data pertinent to this event show an apparent vertical wave phase variation, permitting a very approximate and somewhat uncertain estimate of the wave-associated vertical flux of horizontal momentum, which is found to be about 4 dyn per sq cm. Wave generation by shear instability in the upper tropospheric air flow and the resulting vertical momentum transport may be an important element of the global atmospheric momentum budget.

Hooke, W. H.↗
NASA NTRS1982

Analysis of an existing experiment on the interaction of acoustic waves with a laminar boundary layer

The hot-wire anemometer amplitude data contained in the 1977 report of P. J. Shapiro entitled, ""The Influence of Sound Upon Laminar Boundary'' were reevaluated. Because the low-Reynolds number boundary layer disturbance data were misinterpreted, an effort was made to improve the corresponding disturbance growth rate curves. The data are modeled as the sum of upstream and downstream propagating acoustic waves and a wave representing the Tollmien-Schlichting (TS) wave. The amplitude and phase velocity of the latter wave were then adjusted so that the total signal reasonably matched the amplitude and phase angle hot-wire data along the plate laminar boundary layer. The revised rates show growth occurring further upstream than Shapiro found. It appears that the premature growth is due to the adverse pressure gradient created by the shape of the plate. Basic elements of sound propagation in ducts and the experimental and theoretical acoustic-stability literature are reviewed.

Schopper, M. R.↗
NASA NTRS1993

Determination of plate wave velocities and diffuse field decay rates with braod-band acousto-ultrasonic signals

Lowest symmetric and lowest antisymmetric plate wave modes were excited and identified in broad-band acousto-ultrasonic (AU) signals collected from various high temperature composite materials. Group velocities have been determined for these nearly nondispersive modes. An algorithm has been developed and applied to determine phase velocities and hence dispersion curves for the frequency ranges of the broad-band pulses. It is demonstrated that these data are sensitive to changes in the various stiffness moduli of the materials, in agreement by analogy, with the theoretical and experimental results of Tang and Henneke on fiber reinforced polymers. Diffuse field decay rates have been determined in the same specimen geometries and AU configuration as for the plate wave measurements. These decay rates are of value in assessing degradation such as matrix cracking in ceramic matrix composites. In addition, we verify that diffuse field decay rates respond to fiber/matrix interfacial shear strength and density in ceramic matrix composites. This work shows that velocity/stiffness and decay rate measurements can be obtained in the same set of AU experiments for characterizing materials and in specimens with geometries useful for mechanical measurements.

Kautz, Harold E.↗
NASA NTRS1972

Ionospheric disturbances caused by long period sound waves generated by Saturn-Apollo launches

Wavelike disturbances were observed in the ionosphere following several nuclear explosions in early 1960's. Supersonic shock waves within the atmosphere generated by large rockets can cause ionospheric electron density perturbations. A CW phase path Doppler array in the New York area was operated during the Saturn-Apollo 12 and 13 launches and recorded Doppler frequency fluctuations due to rocket launchings. Cross correlation and power spectral analyses of the phase path-path Doppler frequency variation records showed that the phase velocities of the signal arrivals were from south of the array with 700 - 800 m/sec corresponding to periods in the range of 2 to 4 minutes. Ionograms taken every 60 seconds from Wallops Islands showed clearly ionospheric disturbances due to rockets. The group velocities were estimated to be of the order of 450 m/sec 1 obtained from the earliest visible disturbances seen on CW phase path Doppler records and ionograms together with the rocket trajectory data.

Rao, G. L.↗
NASA NTRS1990

Double-peaked electrostatic ion cyclotron harmonic waves

Electrostatic H(+) cyclotron harmonic waves are often observed along the auroral field lines at altitudes of 1-3.5 R(E) by the Dynamics Explorer 1 satellite. A small fraction of these waves are found to have two peaks associated with each harmonic instead of one peak. The waves occur below the lower hybrid frequency and are usually relatively weak, about a factor of 4 smaller than typical electric field amplitudes of other H(+) cyclotron harmonic wave events. The double-peaked spectral signature is believed to be produced by Doppler shifts arising from the satellite velocity relative to the plasma rest frame. The waves were found to have wavelengths of the order of 300 m and phase velocities of the order of 150 km/s.

Boardsen, S. A.↗
DOE OSTI2018

Spatial distribution of pressure resonance in compressible cavity flow

The development of the unsteady pressure field on the floor of a rectangular cavity was studied at Mach 0.9 using high-frequency pressure-sensitive paint. Power spectral amplitudes at each cavity resonance exhibit a spatial distribution with a streamwise-oscillatory pattern; additional maxima and minima appear as the mode number is increased. This spatial distribution also appears in the propagation velocity of modal pressure disturbances. This behavior was tied to the superposition of a downstream-propagating shear-layer disturbance and an upstream-propagating acoustic wave of different amplitudes and convection velocities, consistent with the classical Rossiter model. The summation of these waves generates a net downstream-traveling wave whose amplitude and phase velocity are modulated by a fixed envelope within the cavity. This traveling-wave interpretation of the Rossiter model correctly predicts the instantaneous modal pressure behavior in the cavity. Here, subtle spanwise variations in the modal pressure behavior were also observed, which could be attributed to a shift in the resonance pattern as a result of spillage effects at the edges of the finite-width cavity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1977

Nonlinear Alfven waves in high-speed solar wind streams

A nonlinear proton distribution function that is an exact stationary solution of the nonlinear Vlasov equation and Maxwell's equations and which supports a single nonlinear transverse Alfven (ion cyclotron) wave that is circularly polarized and nondispersive is proposed for most of the observations during high-speed solar wind streams. This nonlinear distribution removes the strong Alfven wave instability, inconsistent with the persistence of the observed proton distribution functions in high-speed streams, found by the linear stability analysis. Model temperature anisotropies and drift velocities of the two spatially inhomogeneous bi-Maxwellian components are consistent with typical proton velocity distributions measured in high-speed streams at 1 AU. Two derived relations for each of the wave number and the phase velocity of the wave are obeyed within experimental uncertainties by two typical proton measurements. Our model also predicts that the alpha particle bulk flow velocity exceeds the proton particle bulk flow velocity, as is observed.

Abraham-Shrauner, B.↗
DOE OSTI2022

Reconfigurable quantum phononic circuits via piezo-acoustomechanical interactions

Abstract We show that piezoelectric strain actuation of acoustomechanical interactions can produce large phase velocity changes in an existing quantum phononic platform: aluminum nitride on suspended silicon. Using finite element analysis, we demonstrate a piezo-acoustomechanical phase shifter waveguide capable of producing ± π phase shifts for GHz frequency phonons in 10s of μm with 10s of volts applied. Then, using the phase shifter as a building block, we demonstrate several phononic integrated circuit elements useful for quantum information processing. In particular, we show how to construct programmable multi-mode interferometers for linear phononic processing and a dynamically reconfigurable phononic memory that can switch between an ultra-long-lifetime state and a state strongly coupled to its bus waveguide. From the master equation for the full open quantum system of the reconfigurable phononic memory, we show that it is possible to perform read and write operations with over 90% quantum state transfer fidelity for an exponentially decaying pulse.

Taylor, Jeffrey C. (ORCID:0000000215982436)↗
DOE OSTI2022

Interacting quantum and classical waves: Resonant and non-resonant energy transfer to electrons immersed in an intense electromagnetic wave

Dynamics of electrons subjected to a constant amplitude classical electromagnetic (EM) wave is investigated as a fundamental, representative problem in the physics of interacting quantum and classical waves. In the nonrelativistic regime (electrons as Schrödinger waves), the electron energy acquires a constant and a time dependent part. Driven by EM waves, both parts scale strongly with the amplitude, but we expect no resonant enhancement since the parallel electron “speed” of nonrelativistic electrons could never match the wave phase velocity. In the relativistic regime (electron as a Klein–Gordon wave), however, a class of electron waves (with parallel speed matching the EM phase speed) are resonantly excited to extremely high energies. Such a direct resonant energy transfer from intense electromagnetic waves constitutes a mechanism that could, in principle, power the most energetic of cosmic rays (this mechanism will work on protons just as well). Some predictions of the theory will, hopefully, be tested in laboratory laser experiments. In conclusion, the nonrelativistic calculations will also be examined in the context of recent experiments using photon-induced near-field electron microscopy in detail.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1993

Constant frequency pulsed phase-locked loop measuring device

A measuring apparatus is presented that uses a fixed frequency oscillator to measure small changes in the phase velocity ultrasonic sound when a sample is exposed to environmental changes such as changes in pressure, temperature, etc. The invention automatically balances electrical phase shifts against the acoustical phase shifts in order to obtain an accurate measurement of electrical phase shifts.

Yost, William T.↗
NASA NTRS1974

Propagation of transverse waves in a radially expanding plasma

Investigation of the properties of low-frequency transverse waves in an expanding plasma. The wave vector, the background magnetic field, and the streaming velocity of the plasma are all assumed to lie along the radial direction. Expressions are presented for the radial dependence of the amplitude and phase of left and right circularly polarized waves, correct to first order in the wave frequency divided by the proton cyclotron frequency. Differences in the phase velocities of these two circular polarizations result in a Faraday rotation that can be substantial for typical interplanetary conditions near 1 AU. The implications of these results for a realistic solar wind model with the interplanetary magnetic field along the spiral direction are also considered.

Solodyna, C. V.↗
NASA NTRS1990

Ion cyclotron bands in VLF saucers

In the wideband VLF data obtained by the polar orbiting DE-1 satellite over the polar night ion trough region of the upper ionosphere, conspicuous frequency-band structures are found to occur both in absorption and emission, particularly associating with VLF saucers. The attenuation bands indicate that the ions of atomic hydrogen from the polar ionosphere are accelerated by the ac electric fields of VLF waves oscillating normal to the static magnetic field, analogous to a cyclotron accelerator. The observed frequencies of the cyclotron harmonics suggest that the acceleration is taking place in the layer below the satellite at a geocentric distance of less than about 1.5 earth radii. This example indicates the existence of upward propagating hiss at those altitudes inside the auroral zone. On the other hand, the frequency shifts of the emission bands are attributed to a combination of two different types of Doppler shift, one due to the orbital motion of the satellite and the other due to the upward motion of the medium at the emission source. This indicates the existence of an upward plasma flow at the source, with a velocity of the order of 20 km/s inside the saucer. The amount of this frequency shift decreases with increasing harmonic order, indicating a higher phase velocity for the electrostatic waves of higher harmonic order.

Maeda, Kaichi↗
NASA NTRS1994

Plate mode velocities in graphite/epoxy plates

Measurements of the velocities of the extensional and flexural plate modes were made along three directions of propagation in four graphite/epoxy composite plates. The acoustic signals were generated by simulated acoustic emission events (pencil lead breaks or Hsu-Neilson sources) and detected by by broadband ultrasonic transducers. The first arrival of the extensional plate mode, which is nondispersive at low frequencies, was measured at a number of different distances from the source along the propagation direction of interest. The velocity was determined by plotting the distance versus arrival time and computing its slope. Because of the large dispersion of the flexural mode, a Fourier phase velocity technique was used to characterize this mode. The velocity was measured up to a frequency of 160 kHz. Theoretical predictions of the velocities of these modes were also made and compared with experimental observations. Classical plate theory yields good agreement with the measured extensional velocities. For predictions of the dispersion of the flexural mode, Mindlin plates theory, which includes the effects of shear deformation and rotatory inertia was shown to give better agreement with the experimental measurements.

Prosser, W. H.↗
NASA NTRS1994

Fiber-matrix interphase characterization in composites using ultrasonic velocity data

A nondestructive method is introduced to determine the effective elastic of fiber-matrix interphases from measured composite moduli. The composite moduli are obtained by measuring the angular dependences of ultrasonic longitudinal and transverse phase velocities in planes along and perpendicular to the fibers. Three independent interphase effective moduli are found using micromechanical multiphase models which were applied after averaging composite transverse moduli to account for the composite orthotropy. Sensitivity analysis shows that errors in the calculated interphasial moduli are approximately ten times those in the composite moduli. Experiments are performed on Si3N4 ceramic and Ti-24Al-11Nb intermetallic matrix composites reinforced with carbon coated silicon carbide fibers. The experimental interphasial moduli for the intermetallic composites agree with literature data after accounting for the interphase microstructure. The interphasial moduli for ceramic composites are lower than those for the intermetallic composite due to imperfect mechanical contact between the interphase and the porous matrix. The use of the method to assess the interphase degradation is demonstrated for interphasial oxidation damage. The analysis helps to determine the morphology of the damaged interphase.

Chu, Y. C.↗