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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

On the kinetics of volatile loss from chondrites

Data by Lipschutz and coworkers (1975, 1976, 1977) on thermal release of Tl, Bi, and In from primitive chondrites are reexamined to obtain information on the nature and activation energy (E) of release processes: desorption, volume diffusion, and decomposition of the host phase. For the Allende C3 chondrite, the main release for Bi and Tl between 400 and 700 C is shown to be apparently due to desorption of a surface layer, coupled with grain boundary diffusion as the slow step. Further, the main release of In above 600 C and the small tails of Bi and Tl between 700 and 1000 C are observed to represent probably volume diffusion. Results for Abee and other primitive meteorites were found to be essentially similar, except for a very abrupt 500 C release of Tl from Krymka (81%) and Bi from Tieschitz (70%). It is suggested that this release may represent decomposition of a thermolabile phase in a late condensate, such as organic matter or phyllosilicates.

Alaerts, L.↗
NASA NTRS2002

Phase Transition in Dusty Plasmas: A Microphysical Description

Dust grains immersed in plasma discharges acquire a large negative charge and settle into a dust cloud at the edge of the sheath. In this region, the plasma ions stream toward the electrode at a velocity u approx. cs=(T(sub e)/m(sub i))(exp 1/2). Experimentally at sufficiently high gas pressure P, the random kinetic energy of the grains is damped by gas friction, and the grains are strongly coupled and self-organize into a crystalline configuration. For lower pressures despite the dissipation of grain kinetic energy to gas friction, the dust grains reach a steady-state kinetic temperature T(sub d) which is much larger than the temperature of any other component in the plasma. T(sub d) is so large that the dust acts like a fluid. We have used the dynamically shielded dust (DSD) model to simulate these physical processes. We find that the known experimental features are nicely reproduced in the simulations, and that additional features are revealed. In the figure we plot the variation of T(sub d) as P is continuously varied in a DSD code run. A marked difference is evident between the critical pressure P(sub m) for the melting transition as P is decreased, and the critical pressure P(sub c) for the condensation transition as P is increased. For P(sub m) is less than P is less than P(sub c), mixed phase states are seen. This hysteresis occurs because the instability which triggers melting is different from the instability that heats the dust in the fluid phase and inhibits freezing. At low pressure, the dust is subject to a two-stream instability with the ions. This instability is responsible for the high temperature of the dust at low pressure. The basic physics underlying the melting transition has been elucidated in a series of papers. We are developing a first-principles analytic approach to the melting transition, which embodies the same physics that is present in the DSD code.

Joyce, Glenn↗
NASA NTRSDate not supplied

Determination of Interfacial Energy for Solid-State Precipitation

Precipitation of strengthening phases from solid state is a critical process for many materials. For example, the high-temperature creep resistance of Ni-based superalloys is governed by ’ precipitates. However, the interfacial energy which controls the precipitation is expensive to determine experimentally. For simulations, the atomic nature of precipitation events necessitates using Molecular Dynamics (MD) so relying on fitting to a-priori experimental behavior is not required. However, the solid-state precipitation takes orders of magnitude longer time than is accessible for traditional MD simulation. Taking inspiration from Kinetic Monte-Carlo (KMC) methods for simulating diffusion on a rigid lattice, we have developed a hybrid KMC-MD approach to enable simulation of solid-state precipitation (and determination of the interfacial energy). Implementing these methods in LAMMPS, we calculated the interfacial energy for the ’ precipitation out of a super-saturated  phase in Ni-based superalloys. The resulting interfacial energy value for the Ni-Al system is well within the accuracy of experimental values, demonstrating the capability of this method. Enabling the calculation of the interfacial energy without a-priori experimental knowledge of the precipitation unlocks a more efficient ICME-based approach for guiding annealing protocols in Ni-based superalloys and other solid-state precipitation systems.

Precipitation↗
NASA NTRS1981

A three-dimensional simulation of transition and early turbulence in a time-developing mixing layer

The physics of the transition and early turbulence regimes in the time developing mixing layer was investigated. The sensitivity of the mixing layer to the disturbance field of the initial condition is considered. The growth of the momentum thickness, the mean velocity profile, the turbulence kinetic energy, the Reynolds stresses, the anisotropy tensor, and particle track pictures of computations are all examined in an effort to better understand the physics of these regimes. The amplitude, spectrum shape, and random phases of the initial disturbance field were varied. A scheme of generating discrete orthogonal function expansions on some nonuniform grids was developed. All cases address the early or near field of the mixing layer. The most significant result shows that the secondary instability of the mixing layer is produced by spanwise variations in the straining field of the primary vortex structures.

Cain, A. B.↗
NASA NTRS1982

Ejecta of the Ries Crater, Germany

Attention is given to the light which may be shed by the ejecta surrounding the 26-km diameter Ries Crater in West Germany on the Cretaceous-Tertiary Boundary Event. Moldavites represent early high speed ejecta originating at the projectile-target interface. Bunte breccia reflects the major excavation and ejection phase, comprising more than 90 percent of all ejecta beyond the rim crest. Suevite is deposited last, and is derived from the deepest target stratum. Using various scaling laws that relate the bolide's kinetic energy to crater geometry or volume, and assuming a 25 km/sec impact velocity, a 1-2 km projectile diameter is obtained for a stony object. Geochemical studies reveal that projectile dissemination is heterogeneous, and that maximum extraterrestrial contamination modeled as a C1 chondrite is 0.004 wt pct. Observations from this and other terrestrial craters show that tektites and microtectites provide the sole evidence for widespread impact deposits.

Horz, F.↗
NASA NTRS1995

Hybrid simulations of the saturated Farley-Buneman instability in the ionosphere

Numerical simulations of the Farley-Buneman instability in 2-1/2 dimensions using particle ions and fluid electrons show the growth, saturation and nonlinear behavior of two-stream waves. This hybrid technique models the saturated state of the instability for a much longer period of time than the pure particle codes that preceded it. While focusing principally on modeling the topside E region equatorial electrojet, many of these results apply to the auroral two-stream instability as well. The following features are seen in all our hybrid simulations: (1) wave growth at an angle offset from the electron drift direction where the angle depends on the strength of the driving electric field, (2) nonlinear coupling to waves traveling perpendicular to the propagation direction of the principal two-stream waves, (3) a saturated wave phase velocity at or above the sound speed but well below the velocity predicted by linear theory and (4) phase velocities which remain almost constant as a simulated radar sweeps from a horizontal direction to nearly vertical. The nonlinear electron motion dominates the behavior of these waves. Further, these simulations indicate that ion kinetic effects are not essential for the saturation of the instability and that electron temperature effects have a minor impact on the final saturated state.

Oppenheim, Meers↗
NASA NTRS1995

Kinetic simulation of the Kelvin-Helmholtz instability in a finite sized jet

Two-dimensional hybrid simulations with particle ions and fluid electrons are used to calculate the kinetic evolution of the Kelvin-Helmholtz (K-H) instability for a jet of material moving transverse to the magnetic field in the middle of a field reversal region. The instability shows two phases. This first phase is the development of a short scale length instability on the sides of the jet, which might be characterized as a local K-H instability. This instability saturates at low amplitude by modest broadening of the jet profile. Then a nonlocal K-H instability sets in where the jet exhibits a kinklike behavior which spreads and disrupts the jet in a dramatic fashion. The simulation results are discussed within the context of possible relevance to the magnetopause.

Thomas, V. A.↗
NASA NTRS1998

Electron Thermalization in the Solar Wind and Planetary Plasma Boundaries

The work carried out under this contract attempts a better understanding of whistler wave generation and associated scattering of electrons in the solar wind. This task is accomplished through simulations using a particle-in-cell code and a Vlasov code. In addition, the work is supported by the utilization of a linear kinetic dispersion solver. Previously, we have concentrated on gaining a better understanding of the linear mode properties, and have tested the simulation codes within a known parameter regime. We are now in a new phase in which we implement, execute, and analyze production simulations. This phase is projected to last over several reporting periods, with this being the second cycle. In addition, we have started to research to what extent the evolution of the pertinent instabilities is two-dimensional. We are also continuing our work on the visualization aspects of the simulation results, and on a code version that runs on single-user Alpha-processor based workstations.

Krauss-Varban, Dietmar↗
NASA NTRS2018

Update on the NASA Glenn Propulsion Systems Lab Icing and Ice Crystal Cloud Characterization (2017)

NASA Glenn's Propulsion Systems Lab, an altitude engine test facility, generates icing clouds with a spray system. While the spray system is used mostly to create ice crystal clouds (Appendix D/P), the 2017 cloud characterization effort added the requirement to produce exactly supercooled liquid clouds in Appendix C and Appendix O. Success was demonstrated to supercool the largest drops at the warmest conditions, but not freeze out the smallest drops at the coldest conditions. This paper documents primarily the total water content characterization methodology and results from an Iso-Kinetic Probe in ice crystals and Multi-Wire sensor in supercooled liquid, along with the cloud uniformity provided by light extinction tomography. Particle size distribution results from High Speed Imaging probes and a Phase Doppler Interferometer are discussed. Also, a new numerical model for tracking the thermodynamics of the air-drop interactions in PSL from the plenum toward the cloud characterization plane are noted. Both of these latter topic are more fully documented in companion papers.

Calibration↗
NASA NTRS2008

Topological Evolution of a Fast Magnetic Breakout CME in 3-Dimensions

W present the extension of the magnetic breakout model for CME initiation to a fully 3-dimensional, spherical geometry. Given the increased complexity of the dynamic magnetic field interactions in 3-dimensions, we first present a summary of the well known axisymmetric breakout scenario in terms of the topological evolution associated with the various phases of the eruptive process. In this context, we discuss the completely analogous topological evolution during the magnetic breakout CME initiation process in the simplest 3-dimensional multipolar system. We show that an extended bipolar active region embedded in an oppositely directed background dipole field has all the necessary topological features required for magnetic breakout, i.e. a fan separatrix surface between the two distinct flux systems, a pair of spine fieldlines, and a true 3-dimensional coronal null point at their intersection. We then present the results of a numerical MHD simulation of this 3-dimensional system where boundary shearing flows introduce free magnetic energy, eventually leading to a fast magnetic breakout CME. The eruptive flare reconnection facilitates the rapid conversion of this stored free magnetic energy into kinetic energy and the associated acceleration causes the erupting field and plasma structure to reach an asymptotic eruption velocity of greater than or approx. equal to 1100 km/s over an approx.15 minute time period. The simulation results are discussed using the topological insight developed to interpret the various phases of the eruption and the complex, dynamic, and interacting magnetic field structures.

Lynch, B. J.↗
NASA NTRS1972

Further analytical study of hybrid rocket combustion

Analytical studies of the transient and steady-state combustion processes in a hybrid rocket system are discussed. The particular system chosen consists of a gaseous oxidizer flowing within a tube of solid fuel, resulting in a heterogeneous combustion. Finite rate chemical kinetics with appropriate reaction mechanisms were incorporated in the model. A temperature dependent Arrhenius type fuel surface regression rate equation was chosen for the current study. The governing mathematical equations employed for the reacting gas phase and for the solid phase are the general, two-dimensional, time-dependent conservation equations in a cylindrical coordinate system. Keeping the simplifying assumptions to a minimum, these basic equations were programmed for numerical computation, using two implicit finite-difference schemes, the Lax-Wendroff scheme for the gas phase, and, the Crank-Nicolson scheme for the solid phase.

Hung, W. S. Y.↗
NASA NTRS1987

Particle and fluid simulations of resistive current-driven electrostatic ion cyclotron waves

The results from 1-D numerical simulations of electrostatic ion cyclotron waves (EIC) are presented for a model in which the electrons are a resistive (collisional) fluid. Simulations of both the kinetic and fluid descriptions are performed and compared in order to assess the fundamental limitations of fluid theory for EIC waves. The effect of ion-neutral collisions is also included using a simple Monte Carlo technique. It is found that a small ion-neutral collision frequency destroys the frequency harmonic coupling of kinetic EIC waves and tends to validate the fluid description. The saturation amplitude of the current-driven EIC instability is in agreement with recent laboratory experiments. The coherent nature (extremely narrow spectral width) and phase velocity agree with ground based (coherent backscatter radars) and in situ observations of current-driven EIC waves in the high latitude ionosphere.

Seyler, Charles E.↗
NASA NTRS1993

Evaluation of candidate working fluid formulations for the electrothermal-chemical wind tunnel

A new hypersonic test facility which can simulate conditions typical of atmospheric flight at Mach numbers up to 20 is currently under study at the NASA/LaRC Hypersonic Propulsion Branch. In the proposed research, it was suggested that a combustion augmented electrothermal wind tunnel concept may be applied to the planned hypersonic testing facility. The purpose of the current investigation is to evaluate some candidate working fluid formulations which may be used in the chemical-electrothermal wind. The efforts in the initial phase of this research were concentrated on acquiring the code used by GASL to model the electrothermal wind tunnel and testing it using the conditions of GASL simulation. The early version of the general chemical kinetics code (GCKP84) was obtained from NASA and the latest updated version of the code (LSENS) was obtained from the author Dr. Bittker. Both codes are installed on a personal computer with a 486 25 MHz processor and 16 Mbyte RAM. Since the available memory was not sufficient to debug LSENS, for the current work GCKP84 was used.

Akyurtlu, Jale F.↗
NASA NTRS1995

Plasmasphere Modeling with Ring Current Heating

Coulomb collisions between ring current ions and the thermal plasma in the plasmasphere will heat the plasmaspheric electrons and ions. During a storm such heating would lead to significant changes in the temperature and density of the thermal plasma. This was modeled using a time- dependent, one-stream hydrodynamic model for plasmaspheric flows, in which the model flux tube is connected to the ionosphere. The model simultaneously solves the coupled continuity, momentum, and energy equations of a two-ion (H(+) and O(+) quasineutral, currentless plasma. Heating rates due to collisions with ring current ions were calculated along the field line using a kinetic ring current model. First, diurnally reproducible results were found assuming only photoelectron heating of the thermal electrons. Then results were found with heating of the H(+) ions by the ring current during the recovery phase of a magnetic storm.

Guiter, S. M.↗
NASA NTRS2012

Multi-Scale Modeling of Liquid Phase Sintering Affected by Gravity: Preliminary Analysis

A multi-scale simulation concept taking into account impact of gravity on liquid phase sintering is described. The gravity influence can be included at both the micro- and macro-scales. At the micro-scale, the diffusion mass-transport is directionally modified in the framework of kinetic Monte-Carlo simulations to include the impact of gravity. The micro-scale simulations can provide the values of the constitutive parameters for macroscopic sintering simulations. At the macro-scale, we are attempting to embed a continuum model of sintering into a finite-element framework that includes the gravity forces and substrate friction. If successful, the finite elements analysis will enable predictions relevant to space-based processing, including size and shape and property predictions. Model experiments are underway to support the models via extraction of viscosity moduli versus composition, particle size, heating rate, temperature and time.

Olevsky, Eugene↗
NASA NTRSDate not supplied

A Golden Era of PSC Observations From the A-Train By CALIOP and MLS

The fundamental role of polar stratospheric clouds (PSCs) in the depletion of stratospheric ozone is well established. Heterogeneous reactions on PSCs convert the stable chlorine reservoirs HCl and ClONO2 to chlorine radicals that destroy ozone catalytically. PSCs also prolong ozone depletion by delaying chlorine deactivation through the removal of gas-phase HNO3 and H2O by sedimentation of large PSC particles. There has been substantial recent progress in our understanding of PSC processes due to the long-term, vortex-wide observations from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) lidar on the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite and the MLS (Microwave Limb Sounder) on the Aura satellite. The CALIOP observations provide unprecedented high spatial resolution information on particulate aerosol/PSC morphology and composition, while MLS provides complementary collocated measurements of gas-phase HNO3 and H2O, the major constituents of all PSC particles. The combined analyses of these datasets have enabled better PSC composition discrimination and provided valuable new insight into PSC formation processes and particle growth kinetics. The more than 17 years of CALIOP and MLS data have uniquely captured the primary aspects of the seasonal and multi-year variability of PSCs in the Arctic and Antarctic, enabling the development of a state-of-the-art reference PSC data record and climatology. In this presentation, we highlight the significant advances in our understanding achieved during this golden era of spaceborne PSC observations and identify remaining gaps in our knowledge that future spaceborne lidar missions may help resolve.

polar stratospheric clouds↗
NASA NTRS1988

Modeling of wave-coherent pressures in the turbulent boundary layer above water waves

The behavior of air pressure fluctuations induced by progressive water waves generated mechanically in a laboratory tank was simulated by solving a modified Orr-Sommerfeld equation in a transformed Eulerian wave-following frame of reference. Solution is obtained by modeling the mean and wave-coherent turbulent Reynolds stresses, the behavior of which in the turbulent boundary layer above the waves was simulated using a turbulent kinetic energy-dissipation model, properly modified to account for free-surface proximity and favorable pressure gradient effects. The distribution of both the wave-coherent turbulent Reynolds stress and pressure amplitudes and their corresponding phase lags was found to agree reasonably well with available laboratory data.

Papadimitrakis, Yiannis ALEX.↗
NASA NTRS2015

Kinematic and Energetic Properties of the 2012 March 12 Polar Coronal Mass Ejection

We report on the energetics of the 2012 March 12 polar coronal mass ejection (CME) originating from a southern latitude of approximately 60deg. The polar CME is similar to low-latitude (LL) CMEs in almost all respects: three-part morphology; post-eruption arcade (PEA), CME, and filament kinematics; CME mass and kinetic energy; and the relative thermal energy content of the PEA. From polarized brightness images, we estimate the CME mass, which is close to the average mass of LL CMEs. The CME kinetic energy (3.3 × 10(sup 30) erg) is also typical of the general population of CMEs. From photospheric magnetograms, we estimate the free energy (1.8 × 10(sup 31) erg) in the polar crown source region, which we find is sufficient to power the CME and the PEA. About 19% of the free energy went into the CME kinetic energy. We compute the thermal energy content of the PEA (2.3 × 10(sup 29) erg) and find it to be a small fraction (6.8%) of the CME kinetic energy. This fraction is remarkably similar to that in active region CMEs associated with major flares. We also show that the 2012 March 12 is one among scores of polar CMEs observed during the maximum phase of cycle 24. The cycle 24 polar crown prominence eruptions have the same rate of association with CMEs as those from LLs. This investigation supports the view that all CMEs are magnetically propelled from closed field regions, irrespective of their location on the Sun (polar crown filament regions, quiescent filament regions, or active regions).

filaments↗