Search NASA⌕ Search

SEARCH · Search NASA

Results for “Shock waves”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Energetic Particle Abundances as Probes of an Interplanetary Shock Wave

We examine the unique abundance variations of Fe/O and He/H in solar energetic particles from a W09 event of 2001 April 10, that have leaked through the flank of an interplanetary shock launched from W04 on April 9. Shock waves from both events reach the Wind spacecraft on April 11. During the second event, both Fe/O and He/H begin at low values and rise to maxima near the time of passage of the shock waves, indicating greater scattering for the species with the highest rigidity at a given velocity. Strong modulation of Fe/O suggests preferential scattering and trapping of Fe by the wave spectrum near and behind the intermediate shock. A significant factor may be the residual proton-generated waves from the very hard proton spectrum accelerated by the early shock wave prior to the onset of the second event. Thus, ion abundances from the later event probe the residual wave spectrum at the earlier shock.

Reames, D. V.↗
NASA NTRS1992

Cosmic rays and shock waves in active galaxies

Studies of nonthermal radio emission in the inner regions of active galaxies reveal clear morphological evidence for shock waves. It is argued that the shocks are driven by collimated outflow of plasma from the AGN. I describe a model in which the synchrotron radio emission arises from ambient relativistic electrons and magnetic fields which have been compressed in a radiative shock wave. No active particle acceleration at the shock front is required in this picture. The prospects for diagnosing active acceleration from radio continuum and optical emission line observations are briefly discussed.

Wilson, Andrew S.↗
NASA NTRSDate not supplied

Cross-Measurement Comparisons for a CFD Validation Dataset on Mach 2.5 Axisymmetric Turbulent Shock-Wave/Boundary-Layer Interactions

Experimental data for a shock-wave/boundary-layer interaction has been collected using multiple measurement techniques. Unfortunately, diversity of methods for acquisition begets an aggregation of data which does not directly quantify the same properties of the flowfield. The objective in this paper was to (a) present the collection of flowfield measurements in one venue in a format more usable for those validating CFD models against the data, (b) evaluate the degree to which the experimental data support each other, and (c) highlight the differences and relative advantages/shortcomings of each measurement techniques. To present the various measured quantities into common format, CFD results from a companion paper also submitted for presentation at this meeting are utilized. For the case where the boundary layer remains attached, there is agreement between the various measurements as well as with Reynolds-averaged Navier-Stokes simulation solutions. As the impinging shock strength is increased beyond the point of separating the boundary layer, the congruity of the data wanes. Generally, agreement among the measurements exceeds the degree to which the CFD solutions agree with experiments. This suggests that unmodeled physical phenomena, such as transient motion of the reflected shock and separation bubble, give rise to the discrepancies observed in the computational results.

Shock-wave Boundary-layer interaction↗
NASA NTRS1973

Propagation pattern of interplanetary shock waves associated with solar proton flares

The two dimensional pattern of interplanetary shock waves is deduced by taking into account the solar longitude dependence of the time intervals between SSC geomagnetic storms and responsible flares. This pattern near the earth's orbit is not symmetric with respect to the meridian plane which crosses the position of the flare, and the highest speed of this wave propagation is observed in the direction about 30 degrees east of this meridian plane. The magnitude of the Forbush decreases of galactic cosmic rays also varies with the longitude positions of those flares. This is used to estimate the distribution of magnetic fields behind the shock waves.

Sakurai, K.↗
NASA NTRS1983

Shock-wave properties and high-pressure equations of state of geophysically important materials

Shock wave (Hugoniot), shock temperature, and release data are presented for several geophysically important, refractory materials. A sensitive multichannel optical pyrometer was developed to measure shock temperatures (2500 to 5600 K at pressures from 48 to 117 GPa) in anorthite (CaAl2Si2O8) glass. Shock temperatures of 3750 to 6000 K at pressures from 140 to 182 GPa were measured in calcium oxide (CaO). Temperature data were used to constrain the energetics of the B1-B2 phase transition at 70 GPa in CaO, and to construct a finite strain equation of state for CaO consistent with previous Hugoniot data. The CaO equation of state was used with equation of state parameters of other oxides to construct a theoretical mixed oxide Hugoniot of anorthite, which is in agreement with new Hugoniot data above about 50 GPa, determined using experimental techniques developed. The mixed oxide model, however, overestimates the shock temperatures, and does not accurately predict measured release paths.

Boslough, M. B.↗
NASA NTRSDate not supplied

Fluid-Thermal-Structural Interactions in Ramp-Induced Shock-Wave Boundary-Layer Interactions at Mach6

Shock-wave boundary-layer interactions (SWBLI) pose unique challenges for the slender airframes and sharp control surfaces characteristic of high-speed airbreathing aircraft. Spikes in pressure and thermal loading have been shown to occur in SWBLI regions; thus, predicting their location and behavior proves critical for assuring aircraft structural integrity and fatigue resilience. SWBLIs frequently lead to severe turbulent boundary-layer separation and corresponding unsteady motions characterized by a wide range of frequencies. Low-frequency motion has been shown to couple with the structure of a compliant panel, and turbulent boundary layers thus present a particular danger for thin control surfaces. Previous studies have shown that the thermal loading on a compliant panel in a ramp-induced SWBLI may have a signi cant impact on the panel vibrations. A multitude of studies has investigated the heating on rigid structures, but a charactrization of the heating effects on compliant structures is necessary to fully understand the fluid-thermal-structural interactions (FTSI) occurring in ramp-induced SWBLIs. This studuses infrared thermography and high-frequency Kulite pressure transducers to examine the heating loads on rigid and compliant ramps at various angles and flow conditions at Mach 6.

Hypersonic↗
DOE OSTI2025

Ion Acceleration in Fermi-LAT Behind-the-Limb Solar Flares: The Role of Coronal Shock Waves

Here, we investigate the relationship between the gamma-ray emission measured with Fermi-LAT and radio signatures of coronal shock waves in four behind-the-limb (BTL) solar flares. All events were associated with metric type II radio burst. Both start and end times of the radio bursts were synchronized with the gamma-ray emission. The type II bursts associated with the BTL gamma-ray flares had higher speeds and lower formation heights than those of an average sample. These findings support the notion that the highly relativistic ions that produce the gamma-rays in BTL flares are accelerated at CME-driven propagating coronal shock waves rather than in large-scale coronal loops.

Corona↗
NASA NTRS1990

Flow separation in oblique shock wave turbulent boundary layer interactions

Available experimental data on flow separation in shock wave turbulent boundary layer interactions are reviewed at hypersonic and supersonic speeds in two dimensional and axisymmetric interactions. The conditions leading to flow separation and the subsequent changes in the flow are discussed. The effects of the Mach number, Reynolds number, surface cooling and the methods of detecting separation are discussed. Pertinent experimental data for the separated flow characteristics in turbulent boundary layer oblique shock wave interactions are also presented and discussed. Empirical correlations for separated flows are also reviewed.

Hamed, A.↗
NASA NTRS1993

Gas-grain energy transfer in solar nebula shock waves: Implications for the origin of chondrules

Meteoritic chondrules provide evidence for the occurrence of rapid transient heating events in the protoplanetary nebula. Astronomical evidence suggests that gas dynamic shock waves are likely to be excited in protostellar accretion disks by processes such as protosolar mass ejections, nonaxisymmetric structures in an evolving disk, and impact on the nebula surface of infalling 'clumps' of circumstellar gas. Previous detailed calculations of gas-grain energy and momentum transfer have supported the possibility that such shock waves could have melted pre-existing chondrule-sized grains. The main requirement for grains to reach melting temperatures in shock waves with plausibly low Mach numbers is that grains existed in dust-rich zones (optical depth greater than 1) where radiative cooling of a given grain can be nearly balanced by radiation from surrounding grains. Localized dust-rich zones also provide a means of explaining the apparent small spatial scale of heating events. For example, the scale size of at least some optically thick dust-rich zones must have been relatively small (less than 10 kilometers) to be consistent with petrologic evidence for accretion of hot material onto cold chondrules. The implied number density of mm-sized grains for these zones would be greater than 30 m(exp -3). In this paper, we make several improvements of our earlier calculations to include radiation self-consistently in the shock jump conditions, and we include heating of grains due to radiation from the shocked gas. In addition, we estimate the importance of momentum feedback of dust concentrations onto the shocked gas which would tend to reduce the efficiency of gas dynamic heating of grains in the center of the dust cloud.

Hood, L. L.↗
NASA NTRS1973

Reflection of a shock wave from a thermally accommodating wall - Molecular simulation.

Reflection of a plane shock wave from a wall has been simulated on a microscopic scale using a direct simulation Monte Carlo technique of the type developed by Bird. A monatomic gas model representing argon was used to describe the fluid medium and a simple one-parameter accommodation coefficient model was used to describe the gas-surface interaction. The influence of surface accommodation was studied parametrically by varying the accommodation coefficient from zero to one. Results are presented showing the temporal variations of flow field density, and mass, momentum, and energy fluxes to the wall during the shock wave reflection process. The energy flux was used to determine the wall temperature history. Comparisons with experiment are found to be satisfactory where data are available.

Deiwert, G. S.↗