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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 901 records · Page 50
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NASA NTRS1998

Measurements of Heat Transfer, Flow, and Pressures in a Simulated Turbine Blade Internal Cooling Passage

An experimental study was made to obtain quantitative information on heat transfer, flow, and pressure distribution in a branched duct test section that had several significant features of an internal cooling passage of a turbine blade. The objective of this study was to generate a set of experimental data that could be used for validation of computer codes that would be used to model internal cooling. Surface heat transfer coefficients and entrance flow conditions were measured at nominal entrance Reynolds numbers of 45,000, 335,000, and 726,000. Heat transfer data were obtained by using a steady-state technique in which an Inconel heater sheet is attached to the surface and coated with liquid crystals. Visual and quantitative flow-field data from particle image velocimetry measurements for a plane at midchannel height for a Reynolds number of 45,000 were also obtained. The flow was seeded with polystyrene particles and illuminated by a laser light sheet. Pressure distribution measurements were made both on the surface with discrete holes and in the flow field with a total pressure probe. The flow-field measurements yielded flow-field velocities at selected locations. A relatively new method, pressure sensitive paint, was also used to measure surface pressure distribution. The pressure paint data obtained at Reynolds numbers of 335,000 and 726,000 compared well with the more standard method of measuring pressures by using discrete holes.

Russell, Louis M.↗
NASA NTRS1999

Ground-Based Studies of Thermocapillary Flows in Levitated Laser-Heated Drops

The fluid flow phenomena are studied together with the thermal effects on drops levitated in acoustic and/or electrostatic fields. While the study is concerned primarily with particles in strong acoustic fields to overcome gravity, some results for microgravity have also been obtained. The study also includes an analysis and an experimental investigation of the thermocapillary flow in a spot-heated drop. Results of a Glovebox experiment on the MSL-1 mission, one of whose objectives was to evaluate the acoustic stability criteria in microgravity, are also discussed.

Sadhai, S. S.↗
NASA NTRS1972

Magnetospheric access of solar particles and the configuration of the distant geomagnetic field, volume 1

The access of 1.2 to 40 MeV protons and 0.4 to 1.0 MeV electrons from interplanetary space to the polar cap regions was investigated with an experiment on board a low altitude, polar-orbiting satellite (0G0 4). A total of 333 quiet time observations of the electron polar cap boundary give a mapping of the boundary between open and closed geomagnetic field lines. Observations of events associated with co-rotating regions of enhanced proton flux in interplanetary space were used to establish the characteristics of the 1.2 to 40 MeV proton access windows. The results were compared to particle access predictions of the distant geomagnetic tail configurations. The role played by interplanetary anisotropies in the observation of persistent polar cap features is discussed. Special emphasis is given to the problem of nonadiabatic particle entry through regions where the magnetic field is changing direction.

Evans, L. C.↗
NASA NTRSDate not supplied

Intense High-Energy ESP Events and Self-Excited Waves at Inner Heliospheric Distances

Energetic Storm Particle (ESP) events are particle intensity increases associated with the passage of interplanetary (IP) shocks. Although ESP events at 1 AU are usually a low-energy phenomenon (i.e., at proton energies <10 MeV), occasionally they may reach energies of >100 MeV. An analysis of the ESP events observed at proton energies >40 MeV over the last four solar cycles shows that these high-energy particle intensity increases tend to occur when unrelated IP structures such as intervening coronal mass ejections and other unlinked shocks are present in the solar wind through which the IP shock generating the ESP event propagates. The acceleration of particles by IP shocks becomes more efficient when particles repeatedly interact with the traveling shocks. These multiple interactions may be favored by either the effects that these unrelated IP structures produce in the particle transport, or by amplified magnetic field fluctuations excited by the accelerated particles. However, the search for these self-excited waves at IP shocks at 1 AU has been often unsuccessful, with just a handful of events showing enhanced field fluctuations that can resonate with the energetic particles. Modeling results indicate that particle acceleration to the highest energies by the shocks occurs close to the Sun, resulting in large intensities of self-excited waves. We have initiated a search for ESP events in the inner heliosphere with evidence for self-excited waves and few cases observed by Parker Solar Probe will be shown.

David Lario↗
NASA NTRS1982

Dawn-dusk asymmetry of the tail region of the magnetosphere of Saturn and the interplanetary magnetic field

In connection with the findings of the Voyager 1 mission, it appears that the tail lobe of Saturn is very different from that of earth and Jupiter, in that the latter are devoid of energetic particles, and magnetic field lines in this region are thought to be open and interconnecting with the interplanetary magnetic field at large distances in the antisolar direction. The present investigation is concerned with a possible explanation of these observations, taking into account a model of Saturn's magnetosphere. It is shown that the Voyager 1 spacecraft remained in the closed region of the magnetotail during its entire tail traversal and did not have an opportunity to penetrate into the high latitude lobe. It is concluded that Saturn probably has a tail lobe just like earth and Jupiter. However, this tail lobe was not traversed by Voyager.

Akasofu, S.-I.↗
NASA NTRS1999

Low-Frequency Oscillations and Transport Processes Induced by Multiscale Transverse Structures in the Polar Wind Outflow: A Three-Dimensional Simulation

Multiscale transverse structures in the magnetic-field-aligned flows have been frequently observed in the auroral region by FAST and Freja satellites. A number of multiscale processes, such as broadband low-frequency oscillations and various cross-field transport effects are well correlated with these structures. To study these effects, we have used our three-dimensional multifluid model with multiscale transverse inhomogeneities in the initial velocity profile. Self-consistent-frequency mode driven by local transverse gradients in the generation of the low field-aligned ion flow and associated transport processes were simulated. Effects of particle interaction with the self-consistent time-dependent three-dimensional wave potential have been modeled using a distribution of test particles. For typical polar wind conditions it has been found that even large-scale (approximately 50 - 100 km) transverse inhomogeneities in the flow can generate low-frequency oscillations that lead to significant flow modifications, cross-field particle diffusion, and other transport effects. It has also been shown that even small-amplitude (approximately 10 - 20%) short-scale (approximately 10 km) modulations of the original large-scale flow profile significantly increases low-frequency mode generation and associated cross-field transport, not only at the local spatial scales imposed by the modulations but also on global scales. Note that this wave-induced cross-field transport is not included in any of the global numerical models of the ionosphere, ionosphere-thermosphere, or ionosphere-polar wind. The simulation results indicate that the wave-induced cross-field transport not only affects the ion outflow rates but also leads to a significant broadening of particle phase-space distribution and transverse particle diffusion.

Ganguli, Supriya B.↗
NASA NTRS1979

Theory of flux anisotropies in a guiding center plasma

Assuming time stationarity of the one-particle distribution function f on the scale of the bounce motion of particles in a magnetic field, the paper expands the Vlasov equation through O(epsilon) in the adiabatic parameter epsilon, which is the ratio of particle gyroradius to scale length of the magnetic field. Since f is directly proportional to particle flux differential in kinetic energy and solid angle, f is in principle measurable in space experiments, and the present analysis is tailored to be explicitly applicable to space problems. It is shown that the usual expression for the electric field which produces plasma corotation in an axisymmetric system such as a dipole also holds for any nonaxisymmetric but rigidly rotating magnetic field pattern, provided the observed magnetic field is used in place of the dipole field. The analysis is applied to the electric field in a rigidly corotating magnetosphere.

Birmingham, T. J.↗
NASA NTRS1987

Evolution of the axial electron cyclotron maser instability, with applications to solar microwave spikes

The nonlinear evolution of cyclotron radiation from streaming and gyrating electrons in an external magnetic field is analyzed. The nonlinear dynamics of both the fields and the particles are treated fully relativistically and self-consistently. The model includes a background plasma and electrostatic effects. The analytical and numerical results show that a substantial portion of the beam particle energy can be converted to electromagnetic wave energy at frequencies far above the electron cyclotron frequency. In general, the excited radiation can propagate parallel to the magnetic field and, hence, escape gyrothermal absorption at higher cyclotron harmonics. The high-frequency Doppler-shifted cyclotron instability can have saturation efficiencies far higher than those associated with well-known instabilities of the electron cyclotron maser type. Although the analysis is general, the possibility of using this model to explain the intense radio emission observed from the sun is explored in detail.

Vlahos, Loukas↗
NASA NTRS1988

Implications of the GSFC Q3 model for trapped particle motion

The Uranus magnetic field model of Connerney et al. (1987), designated GSFC Q3, is used to compute field geometric invariant parameters that determine the adiabatic motion of energetic charged particles trapped in the Uranian magnetosphere, performing computations only for points located along the Voyager 2 flyby trajectory. The L-shell values computed along the Voyager-2 trajectory were compared with L shell values corresponding to the orbital positions for the Uranian satellites Ariel, Umbriel, Miranda, and Titania for a time period centered on the time of the Voyager 2 closest approach to the planet. Bimodal distributions of L minima asociated with the orbital motion of the moons are obtained, thus complicating the model predictions and correlations with charged particle data. The location of charged particle absorption signatures associated with the sweeping effects of the Uranian satellites is reasonably predicted, but significant discrepancies remain which cannot be explained by Q3 model uncertainties.

Acuna, M. H.↗
NASA NTRS2011

The Solar Wind as a Laboratory for the Study of Magnetofluid Turbulence

The solar wind is the Sun's exosphere. As the solar atmosphere expands into interplanetary space, it is accelerated and heated. Data from spacecraft located throughout the heliosphere have revealed that this exosphere has velocities of several hundred kilometers/sec, densities at Earth orbit of about 5 particles/cm(exp 3), and an entrained magnetic field that at Earth orbit that is about 5 X 10(exp 5) Gauss. A fascinating feature of this magnetized plasma, which is a gas containing both charged particles and magnetic field, is that the magnetic field fluctuates in a way that is highly reminiscent of "Alfven waves", first defined by Hannes Alfven in 1942. Such waves have the defining property that the fluctuating magnetic fields are aligned with fluctuations in the velocity of the plasma and that, when properly normalized, the fluctuations have equal magnitudes. The observed alignment is not perfect and the resulting mismatch leads to a variety of complex interactions. In many respects, the flow patterns appear to be an example of fully developed magnetofluid turbulence. Recently, the dissipation range of this turbulence has been revealed by Search Coil magnetometer data from the four Cluster spacecraft. This tutorial will describe some of the properties of the large-scale and small-scale turbulence.

Goldstein, Melvyn L.↗
NASA NTRS1995

Interactive data exploration and particle tracking for general circulation models

The SCENE environment for interactive visualization of complex data sets is discussed. This environment is used to create tools for graphical exploration of atmospheric flow models. These tools may be extended by the user in a seamless manner, so that no programming is required. A module for accurately tracing field lines and particle trajectories in SCENE is presented. This is used to examine the flowfield qualitatively with streamlines and pathlines and to identify critical points in the velocity field. The paper also describes a visualization tool for general circulation models on which the primary features of the environment are demonstrated.

Rosenbaum, R. I.↗
NASA NTRS1982

Description of the plasma diagnostics package (PDP) for the OSS-1 Shuttle mission and JSC plasma chamber test in conjunction with the fast pulse electron gun (FPEG)

The objectives, equipment, and techniques for the plasma diagnostics package (PDP) carried by the OSS-1 instrument payload of the STS-4 and scheduled for the Spacelab-2 mission are described. The goals of the first flight were to examine the Orbiter-magnetoplasma interactions by measuring the electric and magnetic field strengths, the ionized particle wakes, and the generated waves. The RMS was employed to lift the unit out of the bay in order to allow characterization of the fields, EM interference, and plasma contamination within 15 m of the Orbiter. The PDP will also be used to examine plasma depletion, chemical reaction rates, waves, and energized plasma produced by firing of the Orbiter thrusters. Operation of the PDP was carried out in the NASA Space Environment Simulation Laboratory test chamber, where the PDP was used to assay the fields, fluxes, wave amplitudes, and particle energy spectra. The PDP instrumentation is also capable of detecting thermal ions, thermal electrons suprathermal particles, VHF/UHF EMI levels, and the S-band field strength.

Shawhan, S. D.↗
NASA NTRS1982

Three-dimensional relativistic field-electron interaction in a multicavity high-power klystron. 1: Basic theory

A theoretical investigation of three dimensional relativistic klystron action is described. The relativistic axisymmetric equations of motion are derived from the time-dependent Lagrangian function for a charged particle in electromagnetic fields. An analytical expression of the fringing RF electric and magnetic fields within and in the vicinity of the interaction gap and the space-charge forces between axially and radially elastic deformable rings of charges are both included in the formulation. This makes an accurate computation of electron motion through the tunnel of the cavities and the drift tube spaces possible. Method of analysis is based on Lagrangian formulation. Bunching is computed using a disk model of electron stream in which the electron stream is divided into axisymmetric disks of equal charge and each disk is assumed to consist of a number of concentric rings of equal charges. The Individual representative groups of electrons are followed through the interaction gaps and drift tube spaces. Induced currents and voltages in interacting cavities are calculated by invoking the Shockley-Ramo theorem.

Kosmahl, H. G.↗
NASA NTRS1965

Tail of the magnetosphere.

Tangential stress effects on magnetosphere tail with regard to magnetic field intensity and direction, trapped particle fluxes and low energy cosmic ray cut-off

GEOMAGNETICALLY TRAPPED PARTICLE↗
NASA NTRS1974

Analytical tools and isolation of TOF events

Analytical tools are presented in two reports. The first is a probability analysis of the orbital distribution of events in relation to dust flux density observed in Pioneer 8 and 9 distributions. A distinction is drawn between asymmetries caused by random fluctuations and systematic variations, by calculating the probability of any particular asymmetry. The second article discusses particle trajectories for a repulsive force field. The force on a particle due to solar radiation pressure is directed along the particle's radius vector, from the sun, and is inversely proportional to its distance from the sun. Equations of motion which describe both solar radiation pressure and gravitational attraction are presented.

Wolf, H.↗
NASA NTRS1978

Imp 6 measurements in the distant polar cusp during substorms

High time-resolution data from the magnetic field, plasma, energetic particle, and VLF wave experiments performed aboard Imp 6 in a study of the distant dayside cusp during substorms are described. The cusp was studied when its location was slightly equatorward of its normal location and the geomagnetic dipole was tilted in the appropriate direction. The data support both reconnection and diffusion as methods of particle entry to the magnetosphere. The evidence (1) indicates an acceleration process to explain enhancements of 400 to 600-km/sec protons above their magnetosheath intensities, and (2) suggests convection of field lines over the polar cap as a means of explaining the lack of low-energy protons near the low-latitude boundary of the cusp. Magnetic field fluctuations, a perturbation vector, ion cyclotron waves, and an abrupt change in the intensity of both whistler waves and electrostatic waves are characterized.

Fairfield, D. H.↗
NASA NTRS1985

Fine structure and dynamics of the Harang discontinuity - An event study

Two rockets were launched simultaneously from the Andoya Rocket Range in northern Norway into and through a Harang discontinuity region during a small isolated substorm. Each was equipped with an array of instruments for monitoring ionospheric electric fields and auroral particles. Different sized rockets allowed both to traverse a range of 300 km while introducing altitude separations of up to 440 km, and separations between the feet of the magnetic field lines intersecting the payloads of up to 100 km. The data sets, coupled with multi-station ground-based observations, provide information on the structure and dynamics of the Harang discontinuity region. Two boundaries were encountered. The first electric field reversal was observed simultaneously by both payloads in a region of weak precipitation, while the second reversal was associated with an intense auroral band. Since an unambiguous interpretation of these data is not possible, two alternative scenarios are presented. In one the discontinuity becomes realigned during the flight following a decay in the activity. The second involves a triple cell convection system, possibly the result of an eddy in the flow.

Egeland, A.↗
NASA NTRS1990

Current collection by a long conducting cylinder in a flowing magnetized plasma

The numerical techniques, the definitions, and the normalizations used in the simulations of plasma flow past a long conducting cylinder with a magnetic field along the cylinder axis are described. The effect of cross-field plasma transport on the current collection without any contribution to the current from the field-aligned motion of the plasma particles is highlighted. The electric fields in the structure create a two-cell circulation of the electrons near the cylinder. The cell in the wake region has negative potentials. A fan-shaped circulation cell forms around the cylinder and in this cell the potential is generally positive. The geometry and the size of this positive cell affect the current collection. The potential structure around the cylinder is examined, along with its effect on the current collection and its oscillatory behavior. The variation of the time-average current as a function of the relative motion between the plasma and the cylinder is also investigated.

Singh, Nagendra↗