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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

New waves at multiples of the plasma frequency upstream of the earth's bow shock

The first observations of waves at harmonics higher than the second of the electron plasma frequency are reported. The observations were made by the ISEE 1 spacecraft upstream of the earth's bow shock. The waves are interpreted as electromagnetic radiation at the fundamental and up to the fifth harmonic of the plasma frequency, with effective temperatures decreasing from 5 x 10 to the 17th K to 10 billion K over this range. Two models are proposed for the emission of the waves.

Cairns, I. H.↗
DOE OSTI2018

Modeling The Effects of Shock Pressure and Pore Morphology on Hot Spot Mechanisms in HMX

Here, we investigate the effects of shock pressure and pore morphology on the formation and growth of hot spots in HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine). Both non-reactive and reactive ALE3D simulations are used in these studies. Our non-reactive simulations show a viscous-dominated pore collapse mode at lower shock pressures (2–10 GPa) with shear band formation and a hydrodynamic-dominated mode at higher shock pressures (20-40 GPa) due to bulk melting. When normalized by bulk shock heating, viscous-dominated pore collapse modes are more efficient at generating hot spots. Pore morphology influences the post-collapse temperature distributions and reaction rate for a fixed pore area and shock pressure. We find that multiple surface pores at the binder-grain interface tend to react the fastest. Due to their upstream location in the HMX grain, the surface pores collapse sooner than interior pores; thus, the extent of reaction will generally favor these morphologies because they have more time to grow. In general, multiple smaller hot spots tend to react faster than a single larger hot spot because they accelerate one another's burning. The rank order of morphology effects, however, is not the same for non-reactive and reactive simulations. For example, while multiple surface pores produce the highest reaction rates they do not produce the highest (non-reactive) hot spot temperatures. In conclusion, our numerical studies provide insights on hot spot mechanisms in lieu of direct measurements and can be used to develop advanced shock initiation models.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Effects of air chemistry and stiffened EOS of air in numerical simulations of bubble collapse in water

In this paper we study the effects of a stiffened gas equation of state for air at high pressure and air chemistry with dissociation in numerical simulations of bubble collapse in water. Two types of bubble collapse are studied, with one corresponding to spherically symmetric collapse simulating single-bubble sonoluminescence (SBSL), and the other a GPa-shock-induced axisymmetric bubble collapse. The numerical method is a finite-volume based solver with diffuse material interface model. Verification and validation of the solver are demonstrated by comparing to analytical solutions and experimental observations. We find that for sonoluminescence, air chemistry and equation of state for air at high pressures can have significant effects on the peak temperature and pressure attained during the evolution, and that the peak temperature is on the order of 1 eV, which is close to that observed in experiments. For shock-induced bubble collapse, the pressure inside the bubble will not be as high as that in sonoluminescence due to the absence of spherical symmetry. However, the air chemistry still has a significant effect on the temperature of the bubble. We also examine the effect of multiple bubble interaction in shock-induced bubble collapse and find several mechanisms that can significantly increase the pressure in the water. These mechanisms include frontal-distal-side-collision, shock focusing, upstream-traveling shocks, and compression of the water near the centerline by the vortex generated by bubble collapse. These have important implications for cavitation erosion.

42 ENGINEERING↗
NASA NTRS1979

Pitch angle distributions of energetic protons near the earth's bow shock

Measurements of energetic protons between about 28 and about 145 keV on ISEE-1 upstream and downstream of the earth's bow shock during times of a radial interplanetary magnetic field are presented. The protons exhibited a slight antisunward flow in the spacecraft system in front of the bow shock and a strong flow along the magnetic field in the spacecraft system in the magnetosheath. Compton-Getting transformations of these anisotropies into the plasma frame of reference have been performed. It is argued that the observations can be explained best in terms of particle acceleration by multiple reflection between the bow shock and upstream scattering centers.

Scholer, M.↗
DOE OSTI2023

Effects of Coronal Magnetic Field Configuration on Particle Acceleration and Release during the Ground Level Enhancement Events in Solar Cycle 24

Ground level enhancements (GLEs) are extreme solar energetic particle (SEP) events that are of particular importance in space weather. In solar cycle 24, two GLEs were recorded on 2012 May 17 (GLE 71) and 2017 September 10 (GLE 72), respectively, using a range of advanced modern instruments. Here we conduct a comparative analysis of the two events by focusing on the effects of large-scale magnetic field configuration near active regions on particle acceleration and release. Although the active regions are both located near the western limb, temporal variations of SEP intensities and energy spectra measured in situ display different behaviors at early stages. By combining a potential field model, we find the coronal mass ejection (CME) in GLE 71 originated below the streamer belt, while in GLE 72 it originated near the edge of the streamer belt. We reconstruct the CME shock fronts with an ellipsoid model based on nearly simultaneous coronagraph images from multiple viewpoints and further derive the 3D shock geometry at the GLE onset. The highest-energy particles are primarily accelerated in the shock–streamer interaction regions, i.e., likely at the nose of the shock in GLE 71 and the eastern flank in GLE 72, due to quasi-perpendicular shock geometry and confinement of closed fields. Subsequently, they are released to the field lines connecting to near-Earth spacecraft when the shocks move through the streamer cusp region. This suggests that magnetic structures in the corona, especially shock–streamer interactions, may have played an important role in the acceleration and release of the highest-energy particles in the two events.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Characterization of the dynamic densification behavior of cerium dioxide powders as a function of green density

The uniaxial strain dynamic densification behavior of cerium dioxide powders as a function of powder compact green density is investigated in this work. Cerium dioxide powders of two particle morphologies (rod-like and equiaxed) and two green densities (55% and 62.5% TMD) are shock compressed using the gas gun with specifically designed fixtures and their particle and shock wave velocities are measured using VISAR and multiple PDV probes. The obtained data describe the Hugoniot of the shocked cerium dioxide powders. Finally, the method used to produce this high fidelity Hugoniot data for cerium dioxide powders is discussed and preliminary data are shown.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1974

Multiple pure tone noise generated by fans at supersonic tip speeds

The existence of clusters of pure tones at integral multiples of shaft speed has been noted for supersonic-tip-speed operation of fans and compressors. A continuing program to explore this phenomenon, often called combination-tone noise, has been in effect for several years. This paper reviews the research program, which involves a wide range of engines, compressor rigs, and special apparatus. Elements of the aerodynamics of the blade-associated shock waves are outlined and causes of blade-to-blade shock inequalities, responsible for the multiple tones, are described.

Sofrin, T. G.↗
DOE OSTI2017

Measurements and interpretation of shock tube ignition delay times in highly CO 2 diluted mixtures using multiple diagnostics

Common definitions for ignition delay time are often hard to determine due to the issue of bifurcation and other non-idealities that result from high levels of CO 2 addition. Using high-speed camera imagery in comparison with more standard methods (e.g., pressure, emission, and laser absorption spectroscopy) to measure the ignition delay time, the effect of bifurcation has been examined in this study. Experiments were performed at pressures between 0.6 and 1.2 atm for temperatures between 1650 and 2040 K. The equivalence ratio for all experiments was kept at a constant value of 1 with methane as the fuel. The CO 2 mole fraction was varied between a value of X CO2 = 0.00 to 0.895. The ignition delay time was determined from three different measurements at the sidewall: broadband chemiluminescent emission captured via a photodetector, CH 4 concentrations determined using a distributed feedback interband cascade laser centered at 3403.4 nm, and pressure recorded via a dynamic Kistler type transducer. All methods for the ignition delay time were compared to high-speed camera images taken of the axial cross-section during combustion. Methane time-histories and the methane decay times were also measured using the laser. It was determined that the flame could be correlated to the ignition delay time measured at the side wall but that the flame as captured by the camera was not homogeneous as assumed in typical shock tube experiments. The bifurcation of the shock wave resulted in smaller flames with large boundary layers and that the flame could be as small as 30% of the cross-sectional area of the shock tube at the highest levels of CO 2 dilution. Here, comparisons between the camera images and the different ignition delay time methods show that care must be taken in interpreting traditional ignition delay data for experiments with large bifurcation effects as different methods in measuring the ignition delay time could result in different interpretations of kinetic mechanisms and impede the development of future mechanisms.

03 NATURAL GAS↗
NASA NTRS1972

Study on multi-satellite, multi-measurement of the structure of the earth's bow shock

The pulsation model of the earth's bow shock proposed a nonuniform shock having both perpendicular (abrupt, monotonic) and oblique (oscillatory, multigradient) properties simultaneously, depending on local orientation of the shock surface to the interplanetary field B sub sw in parallel planes defined by B sub sw and solar wind velocity. Multiple, concurrent, satellite observations of the shock and solar wind conditions were used. Twenty-six potentially useful intervals of concurrent Explorer 33 and 35 data acquisition were examined, of which six were selected for closer study. In addition, two years of OGO-5 and HEOS 1 magnetometer data were examined for possible conjunctions to these spacecraft having applicable data. One case of clear nonuniformity and several of field-dependent structure were documented. A computational aid, called pulsation index, was developed.

Source record↗
NASA NTRS1980

Saturn's magnetosphere and its interaction with the solar wind

The paper deals with the Pioneer 11 vector helium magnetometer observations of Saturn's planetary magnetic field, magnetosphere, magnetopause, and bow shock. Models based on spherical harmonic analyses of measurements inside 8 Saturn radii show that the planetary field has a high degree of symmetry about the rotation axis. The vector dipole moment has a tilt angle of less than 1 deg and is offset along the polar axis by 0.04 plus or minus 0.02 Saturn radius. Equatorial offsets derived from the models show pronounced variability and could be consistent with a very small offset. Large impulsive field compressions are observed in the magnetosheath near noon. Multiple crossings of the bow shock are observed, and the absence of significant changes in field direction indicates that it is quasi-perpendicular.

Smith, E. J.↗
NASA NTRS1993

Time-sequenced and spectrally filtered Rayleigh imaging of shock wave and boundary layer structure for inlet characterization

Multiple pulsed Rayleigh imaging and filtered Rayleigh scattering are used to generate images of a complex boundary layer structure, shock wave/boundary layer interactions, and crossing shock waves. Time-sequenced Rayleigh images taken with a visible, double-pulsed laser system show the evolution of boundary layer structure of the internal flow in a generic cross-shock inlet. The images taken in the inlet give insight into 3D effects caused by the inlet geometry and may be used for modeling the complex flows.

Forkey, Joseph↗
NASA NTRS1993

Impact experiments into multiple-mesh targets: Concept development of a lightweight collisional bumper

The utility of multiple-mesh targets as potential lightweight shields to protect spacecraft in low-Earth orbit against collisional damage is explored. Earlier studies revealed that single meshes comminute hypervelocity impactors with efficiencies comparable to contiguous targets. Multiple interaction of projectile fragments with any number of meshes should lead to increased comminution, deceleration, and dispersion of the projectile, such that all debris exiting the mesh stack possesses low specific energies (ergs/sq cm) that would readily be tolerated by many flight systems. The study is conceptually exploring the sensitivity of major variables such as impact velocity, the specific areal mass (g/sq cm) of the total mesh stack (SM), and the separation distance (S) between individual meshes. Most experiments employed five or ten meshes with total SM typically less than 0.5 the specific mass of the impactor, and silicate glass impactors rather than metal projectiles. While projectile comminution increases with increasing impact velocity due to progressively higher shock stresses, encounters with multiple-meshes at low velocity (1-2 km/s) already lead to significant disruption of the glass impactors, with the resulting fragments being additionally decelerated and dispersed by subsequent meshes, and, unlike most contiguous single-plate bumpers, leading to respectable performance at low velocity. Total specific bumper mass must be the subject of careful trade-off studies; relatively massive bumpers will generate too much debris being dislodged from the bumper itself, while exceptionally lightweight designs will not cause sufficient comminution, deceleration, or dispersion of the impactor. Separation distance was found to be a crucial design parameter, as it controls the dispersion of the fragment cloud. Substantial mass savings could result if maximum separation distances were employed. The total mass of debris dislodged by multiple-mesh stacks is modestly smaller than that of single, contiguous-membrane shields. The cumulative surface area of all penetration holes in multiple mesh stacks is an order of magnitude smaller than that in analog multiple-foil shields, suggesting good long-term performance of the mesh designs. Due to different experimental conditions, direct and quantitative comparison with other lightweight shields is not possible at present.

Hoerz, Friedrich↗
DOE OSTI2019

Observations of Multiple Nuclear Reaction Histories and Fuel-Ion Species Dynamics in Shock-Driven Inertial Confinement Fusion Implosions

Fuel-ion species dynamics in DT 3 He-gas-filled Inertial Confinement Fusion implosion is quantitatively assessed for the first time using simultaneously measured D 3 He and DT reaction histories. Here, these reaction histories are measured with the Particle X-ray Temporal Diagnostic, which captures the relative timing between different nuclear burns with unprecedented precision (~10 ps). The observed 50±10 ps earlier D 3 He reaction history timing (relative to DT) cannot be explained by average-ion hydrodynamic simulations, and is attributed to fuel-ion species separation between the D, T, and 3 He ions during shock convergence and rebound. At the onset of the shock burn, inferred 3 He/T fuel ratio in the burn region using the measured reaction histories is much higher as compared to the initial gas-fill ratio. As T and 3 He have the same mass but different charge, these results indicate that the charge-to-mass ratio plays an important role in driving fuel-ion species separation during strong shock propagation.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2016

PLANETARY EMBRYO BOW SHOCKS AS A MECHANISM FOR CHONDRULE FORMATION

We use radiation hydrodynamics with direct particle integration to explore the feasibility of chondrule formation in planetary embryo bow shocks. The calculations presented here are used to explore the consequences of a Mars-size planetary embryo traveling on a moderately excited orbit through the dusty, early environment of the solar system. The embryo’s eccentric orbit produces a range of supersonic relative velocities between the embryo and the circularly orbiting gas and dust, prompting the formation of bow shocks. Temporary atmospheres around these embryos, which can be created via volatile outgassing and gas capture from the surrounding nebula, can non-trivially affect thermal profiles of solids entering the shock. We explore the thermal environment of solids that traverse the bow shock at different impact radii, the effects that planetoid atmospheres have on shock morphologies, and the stripping efficiency of planetoidal atmospheres in the presence of high relative winds. Simulations are run using adiabatic and radiative conditions, with multiple treatments for the local opacities. Shock speeds of 5, 6, and 7 km s{sup −1} are explored. We find that a high-mass atmosphere and inefficient radiative conditions can produce peak temperatures and cooling rates that are consistent with the constraints set by chondrule furnace studies. For most conditions, the derived cooling rates are potentially too high to be consistent with chondrule formation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1987

Stochastic model theory of broadband shock associated noise from supersonic jets

A method based on the work of Tam and Tanna (1982) for calculating the near field noise spectrum and the spatial distribution of broadband shock associated noise from supersonic jets is proposed. Multiple-scales expansion is used to decompose the quasi-periodic shock cells into time-independent waveguide modes of the jet flow, and the interaction of the instability waves with each of the waveguide modes is shown to generate unsteady disturbances which become part of the broadband shock associated noise when radiated to the far field. The observed broadband shock associated noise is composed of a superposition of the various distinct spectra of the different waveguide modes, and the multispectra can be easily identified in many of the existing far and near field noise measurements.

Tam, C. K. W.↗
DOE OSTI2017

First Large-scale Herbig–Haro Jet Driven by a Proto-brown Dwarf

We report the discovery of a new Herbig–Haro jet, HH 1165, in SOAR narrow-band imaging of the vicinity of the σ Orionis cluster. HH 1165 shows a spectacular extended and collimated spatial structure, with a projected length of 0.26 pc, a bent C-shaped morphology, multiple knots, and fragmented bow shocks at the apparent ends of the flow. The H α image shows a bright halo with a clumpy distribution of material seen around the driving source, and curved reflection nebulosity tracing the outflow cavities. The driving source of HH 1165 is a Class I proto-brown dwarf, Mayrit 1701117 (M1701117), with a total (dust+gas) mass of ∼36 M {sub Jup} and a bolometric luminosity of ∼0.1 L {sub ⊙}. High-resolution VLT/UVES spectra of M1701117 show a wealth of emission lines indicative of strong outflow and accretion activity. SOAR/Goodman low-resolution spectra along the jet axis show an asymmetrical morphology for HH 1165. We find a puzzling picture wherein the northwest part exhibits a classical HH jet running into a pre-dominantly neutral medium, while the southern part resembles an externally irradiated jet. The C-shaped bending in HH 1165 may be produced by the combined effects from the massive stars in the ionization front to the east, the σ Orionis core to the west, and the close proximity to the B2-type star HR 1950. HH 1165 shows all of the signatures to be considered as a scaled-down version of parsec-length HH jets, and can be termed as the first sub-stellar analog of a protostellar HH jet system.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

Strong electron heat flux modes in Jupiter's foreshock

Analysis of Voyager plasma wave data from the Jovian foreshock has revealed the existence of a new oscillation with center frequency below fp and typically lying above the upper limit Doppler shift frequency for ion acoustic waves. The properties of these waves are consistent with modes generated by a strong electron heat flux in an unmagnetized plasma. Such modes become unstable when the effective drift velocity exceeds n(cold)/(hot) exp 1/2 times the thermal speed of the hot component. The occasional simultaneous appearance of more than one frequency band is a possible indication of multiple magnetic connection with the shock.

Moses, S. L.↗
NASA NTRS1988

Iridium, shocked minerals, and trace elements across the Cretaceous/Tertiary boundary at Maud Rise, Wedell Sea, and Walvis Ridge, South Atlantic Ocean

Sediments spanning a 5 meter section across the Cretaceous-Tertiary boundary at ODP holes 689B and 690D, Maud Rise, Wedell Sea and hole 527, Walvis Ridge, are being analyzed for shock deformation, PGE's and other trace elements (including REE's). Mineral separates from each sample were studied with optical microscopy to determine the distribution and microstructural state of quartz and feldspar present in the sediments. Samples from Maud Rise were taken of the K/T transition and at about 50 cm intervals above and below it. These samples consist of carbonate-rich sediments, with the K/T transition marked by a change from white Maastrichtian oozes to a greenish ooze with higher concentrations of altered volcanic clay and vitric ash. The Walvis Ridge site is characterized by more clay-rich sediments with average carbonate content about 60 to 70 percent. Initial results from RNAA studies indicate that iridium is present in all the Maud Rise samples in concentrations equal to or greater than 0.01 ppb (whole-rock basis). Preliminary results from optical microscopy indicate the occurrence of shock mosaicism in quartz and feldspar in all of the samples studied. The pervasiveness of shock mosaicism and presence of planar features to 2 meters from the K/T boundary indicates that a single impact or volcanic explosion 66 ma may be ruled out as responsible for the K/T event. A similar conclusion may be drawn independently from the distribution of iridium and other trace elements. Regardless of the source of the shock waves and sediment contamination, multiple events are required over a ca.0.5 my timespan; currently we favor endogenous sources.

Huffman, Alan R.↗