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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 433 records · Page 24
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NASA NTRS1995

Limits on Deceleration and Asymmetry of Solar Wind Speed

It has been suggested by Richardson et al. [1995] that the solar wind shows signs of deceleration due to mass-loading by interstellar pickup ions. They based their conclusion on observations from the Voyager 2 and IMP 8 spacecraft. Observations from the Pioneer Venus Orbiter (PVO), Voyager 2, and Pioneer 10 spacecraft are compared to look for this deceleration. While these comparisons suggests the possibility of deceleration at Voyager 2, the magnitude of this deceleration appears to be significantly less than the deceleration reported by Richardson et al. [1995]. Some of this difference could be explained by a north-south asymmetry in solar wind speed. The implications of these results are discussed, along with possibilities for further investigations.

Gazis, P. R.↗
NASA NTRS1996

Interaction of Particles and Turbulence in the Solar Nebula

The most widely accepted theories for the formation of the Solar system claim that small solid particles continue to settle into a thin layer at the midplane of the Solar nebula until it becomes gravitationally unstable and collapses directly into km-sized planetesimals. This scenario has been challenged on at least two grounds: (1) due to turbulence, the particles may not settle into a thin layer, and (2) a thin layer may not be unstable. The Solar nebula contains at least three sources of turbulence: radial shear, vertical shear, and thermal convection. The first of these is small and probably negligible, while the last is poorly understood. However, the second contribution is likely to be substantial. The particle-rich layer rotates at nearly the Keplerian speed, but the surrounding gaseous nebula rotates slower because it is partly supported by pressure. The resulting shear generates a turbulent boundary layer which stirs the particles away from the midplane, and forestalls gravitational instability. Our previous work used a 'zero-equation' (Prandtl) model to predict the intensity of shear-generated turbulence, and enabled us to demonstrate numerically that settling of particles to the midplane is self-limiting. However, we neglected the possibility that mass loading by particles might damp the turbulence. To explore this, we have developed a more sophisticated 'one-equation' model which incorporates local generation, transport, and dissipation of turbulence, as well as explicit damping of turbulence by particles. We also include a background level of global turbulence to represent other sources. Our results indicate that damping flattens the distribution of particles somewhat, but that background turbulence thickens the particle layer.

Dacles-Mariani, Jennifer S.↗
NASA NTRS2001

Io's Magnetospheric Interaction: An MHD Model with Day-Night Asymmetry

In this paper we present the results of all improved three-dimensional MHD model for Io's interaction with Jupiter's magnetosphere. We have included the day-night asymmetry into the spatial distribution of our mass-loading, which allowed us to reproduce several smaller features or the Galileo December 1995 data set. The calculation is performed using our newly modified description of the pick-up processes that accounts for the effects of the corotational electric field existing in the Jovian magnetosphere. This change in the formulation of the source terms for the MHD equations resulted in significant improvements in the comparison with the Galileo measurements. We briefly discuss the limitations of our model and possible future improvements.

Kabin, K.↗
NASA NTRS2000

Two-Species, 3D, MHD Simulation of Europa's Interaction with Jupiter's Magnetosphere

The interaction of Europa with the Jovian a magnetosphere has been studied by using a two species in ideal magnetohydrodynamic (MHD) numerical model. This model considers the upstream plasma in the Jovian magnetosphere and the molecular oxygen ions in the ionosphere of Europa, separately. We present results a from simulation studies, which take into account impact ionization, recombination, and the effect of a possible induced dipole magnetic field of Europa. The total mass loading of the magnetospheric flow and the ionization frequency used in the model are consistent with the estimates of Europa's ionosphere and atmosphere. The multi-species MHD equations are solved by using a finite volume, high-order, Godunov-type method on an adoptively refined unstructured grid, which allows a detailed modeling of the region near Europa's surface, while still resolving both the upstream region and the satellite's wake. We have paid special attention to the wake of Europa, in order to be able to make comparisons with the Galileo's E4 flyby observations, as well as other model calculations. The calculated escape flux of a O2+ down the tail was found to be about 5.6 x 10(exp 25) s(sup -1).

Liu, Yifan↗
NASA NTRS2001

Wave Activity in Europa's Wake: Implications for Ion Pickup

Intense wave power at frequencies near and below the cyclotron frequencies of heavy ions was detected in Europa's wake during the E11 and E15 flybys. The fluctuations are mainly transverse to the background magnetic field. Wave characteristics indicate that they are ion cyclotron waves driven by positively charged pickup ions. In both flybys there is evidence, derived from the wave polarization, for pickup of negatively charged chlorine ions. When the moon is near the center of the Jovian current sheet, the pickup rate inferred for the E15 flyby is larger than that for the E11 flyby, when the moon is outside the Jovian current sheet. The wave power does not provide exact pickup density values because the waves are observed in regions where their growth has not yet fully developed. At the edges of the wake region, low-frequency (< K+ gyrofrequency) magnetohydrodynamic waves are also present. We identify magnetic field signatures that are reminiscent of interchange/ballooning of mass-loaded flux tubes from the wake/pickup region expanding into ambient medium that is less dense.

Volwerk, M.↗
NASA NTRS2001

Quasi 1-D Analysis of a Circular, Compressible, Turbulent Jet Laden with Water Droplets

Recent experimental studies indicate that presence of small amount of liquid droplets reduces the Overall Sound Pressure Level (OASPL) of a jet. Present study is aimed at numerically investigating the effect of liquid particles on the overall flow quantities of a heated, compressible round jet. The jet is assumed perfectly expanded. A quasi-1D model was developed for this purpose which uses area-averaged quantities that satisfy integral conservation equations. Special attention is given to represent the early development region since it is acoustically important. Approximate velocity and temperature profiles were assumed in this region to evaluate entrainment rate. Experimental correlations were used to obtain spreading rate of shear layer. The base flow thus obtained is then laden with water droplets at the exit of the nozzle. Mass, momentum and energy coupling between the two phases is represented using empirical relations. Droplet size and mass loading are varied to observe their effect on flow variables.

Source record↗
NASA NTRS2002

Decoupling the Role of Particle Inertia and Gravity on Particle Dispersion

Particle dispersion and the influence that particle momentum exchange has on the properties of a turbulent carrier flow in micro-gravity environments challenge present understanding and predictive schemes. The objective of this effort has been to develop and assess high-fidelity simulation tools for predicting particle transport within micro-gravity environments suspended in turbulent flows. The computational technique is based on Direct Numerical Simulation (DNS) of the incompressible Navier-Stokes equations. The particular focus of the present work is on the class of dilute flows in which particle volume fractions and inter-particle collisions are negligible. Particle motion is assumed to be governed by drag with particle relaxation times ranging from the Kolmogorov scale to the Eulerian timescale of the turbulence and particle mass loadings up to one. The velocity field was made statistically stationary by forcing the low wavenumbers of the flow. The calculations were performed using 96(exp 3) collocation points and the Taylor-scale Reynolds number for the stationary flow was 62. The effect of particles on the turbulence was included in the Navier-Stokes equations using the point-force approximation in which 96(exp 3) particles were used in the calculations. DNS results show that particles increasingly dissipate fluid kinetic energy with increased loading, with the reduction in kinetic energy being relatively independent of the particle relaxation time. Viscous dissipation in the fluid decreases with increased loading and is larger for particles with smaller relaxation times. Fluid energy spectra show that there is a non-uniform distortion of the turbulence with a relative increase in small-scale energy. The non-uniform distortion significantly affects the transport of the dissipation rate, with the production and destruction of dissipation exhibiting completely different behaviors. The spectrum of the fluid-particle energy exchange rate shows that the fluid drags particles at low wavenumbers while the converse is true at high wavenumbers for small particles. A spectral analysis shows that the increase of the high wavenumber portion of the fluid energy spectrum can be attributed to transfer of the fluid-particle covariance by the fluid turbulence. This in turn explains the relative increase of small-scale energy caused by small particles observed in the present simulations as well as those of others.

Squires, Kyle D.↗
NASA NTRS2002

The Gas Production Rate and Coma Structure of Comet C/1995 01 (Hale-Bopp)

The University of Wisconsin-Madison and NASA-Goddard conducted a comprehensive multi-wavelength observing campaign of coma emissions from comet Hale-Bopp, including OH 3080 A, [O I] 6300 A, H2O(+) 6158 A, H Balmer-alpha 6563 A, NH2 6330 A, [C I] 9850 A CN 3879 A, C2 5141 A, C3 4062 A, C I 1657 A, and the UV and optical continua. In this work, we concentrate on the results of the H2O daughter studies. Our wide-field OH 3080 A measured flux agrees with other, similar observations and the expected value calculated from published water production rates using standard H2O and OH photochemistry. However, the total [O I] 6300 A flux determined spectroscopically over a similar field-of-view was a factor of 3 - 4 higher than expected. Narrow-band [O I] images show this excess came from beyond the H2O scale length, suggesting either a previously unknown source of [O I] or an error in the standard OH + upsilon to O((sup I)D) + H branching ratio. The Hale-Bopp OH and [O I] distributions, both of which were imaged to cometocentric distances greater than 1 x 10(exp 6) km, were more spatially extended than those of comet Halley (after correcting for brightness differences), suggesting a higher bulk outflow velocity. Evidence of the driving mechanism for this outflow is found in the H(alpha) line profile, which was narrower than in comet Halley (though likely because of opacity effects, not as narrow as predicted by Monte-Carlo models). This is consistent with greater collisional coupling between the suprathermal H photodissociation products and Hale-Bopp's dense coma. Presumably because of mass loading of the solar wind by ions and ions by the neutrals, the measured acceleration of H2O(+) down the ion tail was much smaller than in comet Halley. Tailward extensions in the azimuthal distributions of OH 3080 A, [O I], and [C I], as well as a Doppler asymmetry in the [O I] line profile, suggest ion-neutral coupling. While the tailward extension in the OH can be explained by increased neutral acceleration, the [O I] 6300 A and [C I] 9850 A emissions show 13% and less than 200% excesses in this direction (respectively), suggesting a non-negligible contribution from dissociative recombination of CO(+) and/or electron collisional excitation. Thus, models including the effects of photo-and collisional chemistry are necessary for the full interpretation of these data.

Morgenthaler, Jeffrey P.↗
NASA NTRS2003

Reconciling the MOLA, TES, and Neutron Observations of the North Polar CO2 Mass Budget on Mars

There are now three independent observations of the CO2 polar cap mass budget of Mars' north polar cap. The first is based elevation changes detected by the Mars Orbiter Laser Altimeter (MOLA) on the Mars Global Surveyor (MGS). The second is based on MGS Thermal Emission Spectrometer (TES) broadband observations of the solar and infrared radiation fields at the top of the atmosphere. The third is based on neutron counts measured by the neutron spectrometer (NS) on Odyssey. If one assumes a cap density of 910 kg/cu m, then the peak mass loading poleward of 85 N inferred from the MOLA data is approx. 1090 kg/sq m, which compares to approx. 1150 kg/sq m inferred from TES for the same region, and 700 kg/sq m from the NS data. TES and MOLA are in good agreement, but are about 60% higher than the NS data. Is there a way to reconcile these discrepancies?

Haberle, Robert M.↗
NASA NTRS2003

Optical and Probe Diagnostics Applied to Reacting Flows

We plan to explore three major threads during the fellowship period. The first interrogates the flame synthesis of carbon nanotubes using aerosol catalysts. Laser light scattering will reveal changes in particle size at various heights above the burner. Analysis of the flame gas by mass spectroscopy will reveal the chemical composition of the mixture. Finally, absorption measurements will map the nanotube concentration within the flow. The second thread explores soot oxidation kinetics. Cavity ring-down absorption measurements of the carbonaceous aerosol can provide a measure of the mass concentration with time and, hence, an oxidation rate. Spectroscopic and direct probe measurements will provide the temperature of the system needed for subsequent modeling. The third thread will explore the details of turbulent flame dynamics. Laser induced incandescence will be applied to measurements of soot volume fraction in a 2-d configuration. Analysis of seed tracer particles by planar laser light MIE scattering will reveal the elemental fuel mixture fraction in the flames. Cavity ring-down spectroscopy, a pulsed transient absorption method, will determine the instantaneous mass loading and its fluctuation. Finally, fluorescence measurements will investigate the formation of PAH's in these flames.

Ticich, Thomas M.↗
NASA NTRS1999

Turbulent Concentration of Chondrules: Size Distribution and Multifractal Scaling

Size-selective concentration of particles in 3D turbulence may be related to collection of chondrules and other constituents into primitive bodies in a weakly turbulent protoplanetary nebula. In the terrestrial planet region, both the characteristic size and narrow size distribution of chondrules are explained, whereas "fluffier" particles would be concentrated in lower density, or more intensely turbulent, regions of the nebula. The spatial distribution of concentrated particle density obeys multifractal scaling, suggesting a dose tie to the turbulent cascade process. This scaling behavior allows predictions of the concentration probabilities to be made in the protoplanetary nebula, which are so large (> 10(exp 3) - 10(exp 4)) that further studies must be made of the role of mass loading.

Cuzzi, Jeffrey N.↗
NASA NTRS2002

Effect of surface roughness on liquid property measurements using mechanically oscillating sensors

The resonant frequency and quality factor Q of a liquid immersed magnetoelastic sensor are shown to shift linearly with the liquid viscosity and density product. Measurements using different grade oils, organic chemicals, and glycerol-water mixtures show that the surface roughness of the sensor in combination with the molecular size of the liquid play important roles in determining measurement sensitivity, which can be controlled through adjusting the surface roughness of the sensor surface. A theoretical model describing the sensor resonant frequency and quality factor Q as a function of liquid properties is developed using a novel equivalent circuit approach. Experimental results are in agreement with theory when the liquid molecule size is larger than the average surface roughness. However, when the molecular size of the liquid is small relative to the surface roughness features molecules are trapped, and the trapped molecules act both as a mass load and viscous load; the result is higher viscous damping of the sensor than expected. c2002 Elsevier Science B.V. All rights reserved.

Non-NASA Center↗
NASA NTRS2004

In-Situ Measurements of Aerosol Optical Properties using New Cavity Ring-Down and Photoacoustics Instruments and Comparison with more Traditional Techniques

Carbonaceous species (BC and OC) are responsible for most of the absorption associated with aerosol particles. The amount of radiant energy an aerosol absorbs has profound effects on climate and air quality. It is ironic that aerosol absorption coefficient is one of the most difficult aerosol properties to measure. A new cavity ring-down (CRD) instrument, called Cadenza (NASA-ARC), measures the aerosol extinction coefficient for 675 nm and 1550 nm light, and simultaneously measures the scattering coefficient at 675 nm. Absorption coefficient is obtained from the difference of measured extinction and scattering within the instrument. Aerosol absorption coefficient is also measured by a photoacoustic (PA) instrument (DRI) that was operated on an aircraft for the first time during the DOE Aerosol Intensive Operating Period (IOP). This paper will report on measurements made with this new instrument and other in-situ instruments during two field recent field studies. The first field study was an airborne cam;oaign, the DOE Aerosol Intensive Operating Period flown in May, 2003 over northern Oklahoma. One of the main purposes of the IOP was to assess our ability to measure extinction and absorption coefficient in situ. This paper compares measurements of these aerosol optical properties made by the CRD, PA, nephelometer, and Particle Soot Absorption Photometer (PSAP) aboard the CIRPAS Twin-Otter. During the IOP, several significant aerosol layers were sampled aloft. These layers are identified in the remote (AATS-14) as well as in situ measurements. Extinction profiles measured by Cadenza are compared to those derived from the Ames Airborne Tracking Sunphotometer (AATS-14, NASA-ARC). The regional radiative impact of these layers is assessed by using the measured aerosol optical properties in a radiative transfer model. The second study was conducted in the Caldecott Tunnel, a heavily-used tunnel located north of San Francisco, Ca. The aerosol sampled in this study was characterized by fresh automobile and diesel exhaust. Measurements from Cadenza and from an aethalometer are presented. The aethalometer is a filter-based photometer and the infrared channel is calibrated to produce a measure of BC mass loading.

Strawa, A. W.↗
NASA NTRS2004

Preliminary Interpretation of Ambient Pickup Ions at Titan Observed by the Cassini Plasma Spectrometer

The Cassini Plasma Spectrometer (CAPS) instrument is scheduled to observe the plasma environment at Titan October 26,2004 from the Cassini Orbiter. Preliminary CAPS ion measurements from this encounter will be compared with measurements made by the Voyager I Plasma Science Instrument (PSI). The comparison will be used to evaluate previous interpretations and predictions of the Titan plasma environment that have been made using PSI measurements. The comparisons will focus on the composition and nature of the ambient plasma and pickup ions. Using the CAPS ion measurements, some of the questions to be addressed, as stimulated by the previous interpretations and predictions made evaluating PSI data, are the following: A) Are H+ and N+ the major ion components of Saturn's rotating magnetosphere in the vicinity of Titan? B) Are other ambient ions present? C) Are finite gyroradius effects apparent in ambient N+ as the result of its interaction with Titans atmosphere? D) Are the principal pickup ions composed of H+, H2+, N+, N2+ and CH4+? E) Is the dominant pickup ion closest to Titan's ionopause N2+? F) Is there evidence of slowing down of the ambient plasma due to pickup ion mass loading? F) If so, does the ambient plasma slow down rapidly, as the ionopause is approached and heavier pickup ions like N2+ are added? During the Voyager I flyby, Titan was in Saturn's magnetosphere. If Titan is in Saturn's magnetosheath or the solar wind at the encounter, questions similar to the above will be addressed as appropriate.

Hartle, R. E.↗
NASA NTRS1947

Preliminary Evaluation of the Spin and Recovery Characteristics of the Douglas XF3D-1 Airplane

A preliminary evaluation of the spin and recovery characteristics of the XF3D-1 airplane has been made, based primarily on the results of the free-spinning tunnel tests of a model which closely simulated the XF3D-1 in tail design, tail length, and mass loading. Estimates have been made of the rudder-pedal force that may be encountered in effecting recovery from a spin and of the spin recovery parachute requirements of the airplane for demonstration spins. The method of bail-out which should be used if it becomes necessary for the crew to abandon the airplane during a spin is indicated. It was indicated that the recovery characteristics of the XF3D-1 airplane in the clean condition for erect and inverted spins would be satisfactory for all loadings specified by the contractor as possible on the airplane. However, if a spin is inadvertently entered while the landing flaps are down, recovery may be slow. The slow-down brakes and the landing flaps should be retracted immediately upon the inception of a spinning condition, after which recovery from the spin should be attempted. The pedal force necessary to reverse the rudder during a spin will be within the physical capabilities of the pilot. Opening a 10-foot diameter parachute attached to the tail (laid-out-flat diameter, drag coefficient 0.7) or a 4.5-foot diameter parachute attached to the outboard wing tip will insure satisfactory spin recovery from demonstration spins. If it becomes necessary for the crew to abandon the airplane during a spin, they should leave from the outboard side of the cockpit.

Scher, Stanley H.↗
NASA NTRS2005

Preliminary Interpretation of Titan Plasma Interaction as Observed by the Cassini Plasma Spectrometer: Comparisons With Voyager 1

The Cassini Plasma Spectrometer (CAPS) instrument made measurements of Titan s plasma environment when the Cassini Orbiter flew through the moon s plasma wake October 26,2004 (flyby TA) and December 13,2004 (flyby TB). Preliminary CAPS ion and electron measurements from these encounters (1,2) are compared with measurements made by the Voyager I Plasma Science Instrument (PLS). The comparisons are used to evaluate previous interpretations and predictions of the Titan plasma environment that have been made using PLS measurements (3,4). The plasma wake trajectories of flybys TA, TB and Voyager 1 are similar because they occurred when Titan was near Saturn s local noon. These similarities make possible direct, meaningful comparisons between the various plasma wake measurements. The inquiries stimulated by the previous interpretations and predictions made using PLS data have produced the following results from the CAPS ion measurements: A) The major ambient ion components of Saturn s rotating magnetosphere in the vicinity of Titan are H+, H2+, and O+. B) Finite gyroradius effects are apparent in ambient 0 as the result of its interaction with Titan s atmosphere. C) The principal pickup ions are composed of H+, H2+, CH4+ and N2+. D) There is clear evidence of slowing down of the ambient plasma due to pickup ion mass loading; and, as the ionopause~ is approached, heavier pickup ions such as N2+ become dominant. The similarities and differences between the magnitudes and structures of the electron densities and temperatures along the three flyby trajectories are described

Hartle, R. E.↗
NASA NTRS2005

Loss of Water from Saturn's E-Ring Through Ion Pick-Up

One of the possible loss processes for Saturn s E-ring is ionization followed by acceleration by the electric field associated with the corotating magnetized plasma. It is possible to determine if this process is occurring by detecting electromagnetic waves at the gyrofrequency of water group ions. If the energy the particle gains in this pick-up process is sufficiently great, the picked up ions will generate ion cyclotron waves. Pioneer 11 and Voyager 1 both observed intervals of such waves associated with water group ions during their passes through Saturn s E-ring. Presently the magnetometer onboard the Cassini spacecraft is also seeing water group ion cyclotron oscillations. The Cassini data allow the spatial and temporal behavior of the waves to be mapped in ways not possible during the previous flybys. Analyses of these waves allow us to study the rate of mass loading and its latitudinal and local time variation. In conjunction with previous data, we can then determine the variation as the inclination of the ring to the Sun changes, in accordance with Saturn's seasons. These waves may be the clue to how Saturn powers its magnetosphere as the newly born ions could be the driver for the radial motion of the plasma and to how the E-ring may play the equivalent role to that of Io in the jovian magnetosphere.

Leisner, J. S.↗
NASA NTRS2005

Compilation of Published Estimates of Annual Geocenter Motions Using Space Geodesy

The definition of the term "geocenter motion" depends on the adopted origin of the reference frame. Common reference frames used in Space Geodesy include: the center of mass of the whole Earth (CM), the center of mass of the Solid Earth without mass load (CE), and the center of figure of the outer surface of the Solid Earth (CF). There are two established definitions of the term geocenter: one, the vector offset of CF relative to CM and, two, the reverse, the vector offset of CM relative to CF. Obviously, their amplitude is the same and their phase differs by 180 deg. Following Dong et al. [2003], we label the first X(sub CF, sup CM) and the second X(sup CF, sup CM) (i.e., the superscript represents the frame, the subscript represents any point in the frame).

Elosegui, P.↗