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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Inertial transfers in the helical decomposition

The directions of the triadic energy transfers assumed in a previous paper agree with the spectral closures, in a similarity range, if the exponent of the power-law energy spectrum is less than unity. The helical interactions showing a strong local energy transfer when the triad is nonlocal, sum up to a reverse cascade unless the spectrum falls off faster than a -7/3 power of the wave number. The energy cascades from each type of helical interaction are calculated for a -5/3 inertial range using the eddy damped quasinormal Markovian model. One type of interaction is responsible for 86 percent of the cascade. The contributions of the two classes of helical interactions to the subgrid-scale eddy viscosity are presented, together with the contributions from the forward and reverse cascading interactions. An application of the assumption on the triadic energy transfers to turbulence under rapid rotation gives a simple argument for the tendency toward nonlinear two-dimensionalization of the flow.

Waleffe, Fabian↗
NASA NTRS1980

A suggestion concerning the generation of the physical state of stellar mantles

The physical state of the winds of B supergiants varies from one of a high level of ionization and rapid outflow to one of relatively low ionization and a moderate rate of outflow as one goes from type B0 to type A0. It is proposed here that this is the result of magnetodynamic energy being released in the mantles of these stars, much as occurs in the sun. Data are presented to show that this idea is plausible. It is noted that the release of magnetodynamic energy as the result of interaction between magnetic fields and differential motion in an inhomogeneous structure is probably the cause of the heating in all outer stellar atmospheres (mantles). In the late-type stars, the material in the mantle must first be ionized by the deposition of energy from acoustic waves; in the early-type stars, the material is already ionized at least once in the photosphere, as a result of the normal transfer of radiative energy, so no priming process is necessary for these stars.

Underhill, A. B.↗
NASA NTRS1987

Ab initio studies of low-lying 3Sigma(-), 3Pi, and 5Sigma(-) states of NH. I - Potential curves and dipole moment functions

Configuration interaction wave functions, potential energy curves, and dipole moment functions have been calculated for the four lowest 3Sigma(-) and the three lowest 3Pi states and 5Sigma(-) states of NH. The electronic wave functions were constructed to give a balanced description of valence-Rydberg interactions. Two repulsive states have been identified as important photodissociation pathways. Spectroscopic constants are presented for the bound states, and results are compared to other theoretical and experimental work. The possible predissociation of the A 3Pi state by the 1 5Sigma(-) state is discussed.

Goldfield, Evelyn M.↗
NASA NTRS1985

Rossby waves in opposing currents

A barotropic Rossby wave incident to a region of increasing mean flow velocity opposing the wave group velocity undergoes a reversal of direction at a stopping point where the mean flow velocity and local wave group velocities are equal and opposite. Incident wave amplitude increases approaching this stopping point, which may be referred to as a group velocity critical layer, but eventually suffers a decrease along its trajectory so that the reflected wave amplitude and energy tend to zero on approach to a phase velociy critical layer located where the opposing flow vanishes. Some applications of this process to observations of synoptic scale Rossby waves are suggested and an axample of the interaction of an incident wave with a barotropic model of the Hadley circulation is presented to illustrate these ideas.

Farrell, B.↗
NASA NTRS1989

Long-Wavelength Infrared Detector

Proposed device detects infrared photons of 10- to 100-micrometer wavelength by intersubband absorption in coupled quantum wells. Based on splitting of energy level occuring when two quantum wells placed so close together wave functions of quantized energy levels overlap. Detector absorbs photons, energy which equals difference in energy between two levels resulting from split. Because degree of overlap of wave functions and, therefore, magnitude of split varied by varying width of barrier between two coupled wells, such detector, in principle, designed to operate at any desired wavelength. Restrictions on design parameters of quantum wells of proposed device less severe than single-well devices. Energy levels near tops of wells still necessary so photoexcited carriers tunnel out. Additional flexibility in design obtained by use of wells formed by barriers of different heights.

Vasquez, Richard P.↗
NASA NTRS1984

Kristian Birkeland - The man and the scientist

A review is presented of Birkeland's outstanding contributions to auroral theory and, in particular, to the foundation of modern magnetospheric physics. Birkeland's first years in research, after a study of mathematics and theoretical physics at the university, were concerned with Maxwell's theory, the investigation of electromagnetic waves in conductors, wave propagation in space, an energy transfer by means of electromagnetic waves, and a general expression for the Poynting vector. Experiments with cathode rays near a magnet in 1895, led Birkeland to the development of an auroral theory. This theory represented the first detailed, realistic explanation of the creation of an aurora. Attention is given to experiments conducted to verify the theory, the discovery of the polar elementary storm, and the deduction of auroral electric currents. Birkeland's background and education is also considered along with his personality.

Egeland, A.↗
NASA NTRS2007

Modeling the Observed Solar Cycle Variations of the Quasi-biennial Oscillation (QBO): Amplification by Wave Forcing

In several papers, the solar cycle (SC) effect in the lower atmosphere has been linked observationally to the Quasi-biennial Oscillation (QBO) of the zonal circulation, which is generated primarily by small-scale gravity waves (GW). Salby and Callaghan (2000) in particular analyzed the QBO, covering more than 40 years, and discovered that it contains a large SC signature at 20 km. With our Numerical Spectral Model (NSM), we conducted a 3D study to describe the QBO under the influence of the SC, and some results have been published (Mayr et al., GRL, 2005,2006). For a SC period of 10 years, the relative amplitude of radiative forcing is taken to vary exponentially with height, i.e., 0.2% at the surface, 2% at 50 km, 20% at 100 km and above. Applying spectral analysis to filter out and identify the SC signature, the model generates a relatively large modulation of the QBO, which reproduces the observations qualitatively. Our numerical results demonstrate that the modulation of the QBO, with constant phase relative to the SC, persist at least for 60 years. The same model run generates in the seasonal variations a hemispherically symmetric Equatorial Annual Oscillation (EAO, with 12-month period), which is confined to low latitudes like the QBO and is also modulated by the SC. Although the amplitude of the EAO is relatively small, its SC modulation is large, and it is in phase with that of the QBO. The SC modulated EAO is evidently the pathway and pacemaker for the solar influence on the QBO. To shed light on the dynamical processes involved, we present model results that show how the seasonal cycle induces the SC modulations of the EAO and QBO. Our analysis further demonstrates that the SC modulations of the QBO and EAO are amplified by the GW interaction with the flow. The GW momentum source clearly shows a SC modulation that is in phase with the corresponding modulations of the QBO and EAO. By tapping the momentum from the upward propagating GWs, the QBO and EAO apparently serve as conduits to amplify and transfer to lower altitudes the larger SC variations in the UV absorbed in the mesosphere. Our model also produces in the temperature variations of the QBO and EAO measurable SC modulations at polar latitudes near the tropopause, and such signatures have been reported in the literature. Contrary to conventional interpretation, however, we suggest that the effects are generated at least in part by the meridional circulation, and planetary waves presumably, which redistribute the energy from the equatorial region where wave forcing is very efficient and thereby amplifies the SC influence.

Mayr, Hans G.↗
NASA NTRS1973

Excited electronic states of O2/-/.

Configuration interaction (CI) variational trial functions (which assure formally correct dissociation) and the single-configuration self-consistent-field approximation are applied to the calculation of the excited electronic states of the negatively charged oxygen molecule. The energy curves and wave functions of these states are analyzed. All the excited states are found to have equilibrium-internuclear separations at least 1 a.u. larger than the ground state. The two lowest energy states are characterized, respectively, as shape and valence Feshbach resonances.

Krauss, M.↗
NASA NTRS1986

Thermal ion heating in the vicinity of the plasmapause: A Dynamics Explorer guest investigation

The ion thermal structure of the plasmasphere was investigated in a series of experiments. It appears that energy may be generally available to ion and electrons in the vinicity of the plasmapause from Coulomb interactions between ambient thermal plasma and low energy ring current and suprathermal ions, particularly O+. The amount of energy transferred depends on the densities and energies of each of the components. The spatial distribution of heating in turn depends critically on the spatial distribution of the different populations, especially on the density gradients. The spatial distribution of the thermal plasma is found to vary significantly on a diurnal time scale and is complicated by the plasmasphere erosion and refilling processes associated with magnetic activity and its aftermath. Thermal ion composition also appears to be influenced by the heating taking place, often increasing the heavy ion population in the vicinity of the plasmapause. The observations of equatorial heating near the plasmapause in the presence of equatorial noise also raise the likelihood of a wave source of energy. It is not unreasonable to expect that both particle and wave heat sources are significant, although not necessarily at the same times and places.

Comfort, R. H.↗
NASA NTRS2018

Magnetostrictive Alternator

A magnetostrictive alternator configured to convert pressure waves into electrical energy is provided. It should be appreciated that the magnetostrictive alternator may be combined in some embodiments with a Stirling engine to produce electrical power. The Stirling engine creates the oscillating pressure wave and the magnetostrictive alternator converts the pressure wave into electricity. In some embodiments, the magnetostrictive alternator may include aerogel material and magnetostrictive material. The aerogel material may be configured to convert a higher amplitude pressure wave into a lower amplitude pressure wave. The magnetostrictive material may be configured to generate an oscillating magnetic field when the magnetostrictive material is compressed by the lower amplitude pressure wave.

Dyson, Jr., Rodger W.↗
NASA NTRS1967

Experiments in low energy plasmas

Electron energy loss in afterglow plasmas, plasma transport and stability and electromagnetic wave propagation through magnetoplasmas

MAGNETOPLASMA↗
NASA NTRS1980

Radiation damping of long, finite-amplitude internal waves

Numerical solutions of a damped, nonlinear wave equation are presented. The equation describes the propagation of waves in a narrow thermocline or inversion which lose energy by exciting internal waves in the weakly stratified ambient environment. The results provide estimates for the persistence of finite-amplitude internal waves propagating in a thermoclinic waveguide.

Pereira, N. R.↗
NASA NTRS1980

Turbulence Modeling for Unsteady Transonic Flows

Conditionally sampled, ensemble-averaged velocity measurements, made with a laser velocimeter, were taken in the flowfield over the rear half of an 18% thick circular arc airfoil at zero incidence tested at M = 0.76 and at a Reynolds number based on chord of 11 x 10(exp 6). Data for one cycle of periodic unsteady flow having a reduced frequency f of 0.49 are analyzed. A series of compression waves, which develop in the early stages of the cycle, strengthen and coalesce into a strong shock wave that moves toward the airfoil leading edge. A thick shear layer forms downstream of the shock wave. The kinetic energy and shear stresses increase dramatically, reach a maximum when dissipation and diffusion of the turbulence exceed production, and then decrease substantially. The response lime of the turbulence to the changes brought about by the shock-wave passage upstream depends on the shock-wave strength and position in the boundary layer. The cycle completes itself when the shock wave passes the midchord, weakens, and the shear layer collapses. Remarkably good comparisons are found with computations that employ the time-dependent Reynolds averaged form of the Navier-Stokes equations using an algebraic eddy viscosity model, developed for steady flows.

Marvin, J. G.↗
NASA NTRS1980

Turbulence Modeling for Unsteady Transonic Flows

Conditionally sampled, ensemble-averaged velocity measurements, made with a laser velocimeter, were taken in the flowfield over the rear half of an 18% thick circular arc airfoil at zero incidence tested at M = 0.76 and of a Reynolds number based on chord of 11 x 10(exp 6). Data for one cycle of periodic unsteady flow having a reduced frequency bar-f of 0.49 are analyzed. A series of compression waves, which develop in the early stages of the cycle, strengthen and coalesce into a strong shock wave that moves toward the airfoil leading edge. A thick shear layer forms downstream of the shock wave. The kinetic energy and shear stresses increase dramatically, reach a maximum when dissipation and diffusion of the turbulence exceed production, and then decrease substantially. The response time of the turbulence to the changes brought about by the shock-wave passage upstream depends on the shock-wave strength and position in the boundary layer. The cycle completes itself when the shock wave passes the midchord, weakens, and the shear layer collapses. Remarkably good comparisons are found with computations that employ the time-dependent Reynolds averaged form of the Navier-Stokes equations using an algebraic eddy viscosity model, developed for steady flows.

Marvin, J. G.↗
NASA NTRS2000

Theoretical Technology Research for ISTP/SOLARMAX

During the last decade, we have been developing theoretical tools to support the scientific objectives of the International Solar Terrestrial Physics (ISTP) program. Results from our mission-oriented theory program have contributed significantly to the development of predictive capabilities by using real upstream solar wind conditions as input to our models and forecasting events observed downstream near Earth. We also developed the capability to unravel the complex information contained in ion velocity distribution functions measured near the Earth to determine their origin and energization process. During solar maximum, solar flares and coronal mass ejections (CMEs) dominate the sun's activity. It is now widely accepted that the impact of CMEs (or magnetic clouds) with the Earth's magnetosphere is the cause of most magnetic storms during solar maximum. One important aspect of a CME is the occurrence of solar energetic particle (SEP) events. During these events, protons, electrons, and heavy ions of solar origin are accelerated to very high energies by shock waves driven out from the sun. We carried out a series of large-scale kinetic (LSK) simulations to model the effect of SEPs on the near-Earth environment and the accessibility of these high-energy particles to the inner magnetosphere. We present the results of these studies.

Ashour-Abdalla, Maha↗
NASA NTRS1995

Three-fluid solar wind model with Alfven waves

We present a study of a three-fluid solar wind model. with continuity, momentum and separate energy equations for protons. alpha particles and electrons. Allowing separate coronal heat sources for all three species, we study the flow properties of the solar wind as a function of heat input, Alfven wave energy input, and alpha particle abundance.

Esser, Ruth↗
NASA NTRS1993

Kinetic physics of the mirror instability

Kinetic mechanisms for the growth and saturation of the mirror instability are described using one-dimensional hybrid simulations. Two parameter regimes are considered. In the first regime, a relatively small ion anisotropy excites a slowly growing instability that produces small-amplitude waves; most ions respond to the waves as an adiabatic fluid. In the second regime a large anisotropy excites a rapidly growing instability that generates large-amplitude waves; the response of many ions in this case is nonadiabatic. The difference in ion response is due to the relative importance of two ion populations, resonant and nonresonant. Resonant ions, those ions with low velocities parallel to the background magnetic field, contribute to the growth of the instability as a result of their gyrointeractions with the noncoplanar component of the waves electric field and respond to the mirror waves nonadiabatically. Nonreasonant ions, those with large parallel velocities, respond as an adiabatic fluid. In both regimes, ion anisotropy is reduced by means of the magnetic mirror force; in the second regime, the anisotropy reduction reduces the free energy available for wave growth and leads to the saturation of the mirror instability.

Mckean, M. E.↗
NASA NTRS1987

On the polarization, compression and nonoscillatory behavior of hydromagnetic waves associated with pickup ions

Solution of the kinetic dispersion equation shows that heavy pickup ions with large perpendicular energies excite a new hydromagnetic wave mode with maximum growth, high (magnetic field and mass density) compression ratios, and almost linear polarization coexisting slightly away 6-15 deg from parallel propagation. The mode arises from the coupling of the heavy ion beam to the modified left-hand wave dispersion caused by the multiion nature of the medium. The ion beam can also bring about nonoscillatory, purely growing structures distinct from the mirror wave through the coupling of a counter-streaming left-hand mode to a costreaming right-hand wave. The free energy source parameters are varied to determine their relative influence and define the domain of existence of the instability. Its characteristics may prove helpful in the interpretation of recent cometary (Halley and Giacobini-Zinner) and artificial release (AMPTE) observations.

Brinca, Armando L.↗