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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

The modulation features of the long-period cosmic ray variations in connection with the sign change of the general magnetic field of the Sun

On the basis of the model and experimental investigations, the spatial distribution of cosmic ray anisotropy for the different epochs of solar activity is studied. A solution is offered to the anisotropic diffusion equation with regard to the electromagnetic conditions for the periods of minimum and maximum solar activity and cosmic ray particle drift in a regular interplanetary magnetic field. It is shown that the long period changes amplitude and phase of the diurnal variations of cosmic rays is limited not only by convection and diffusion of particles but also by the drift effect before and after the sing change of the general magnetic field of the Sun. The calculated model is compared with the results obtained on the basis of an analysis of the experimental data from the neutron super monitor station, and it is shown that for the periods when the lines of magnetic force of the Sun come from the Northern Hemisphere the phase of the first harmonic diurnal variation is shifted forwards to an earlier time.

Iskra, K.↗
NASA NTRS1995

Characteristics of ionospheric convection and field-aligned current in the dayside cusp region

The assimilative mapping of ionospheric electrodynamics (AMIE) technique has been used to estimate global distributions of high-latitude ionospheric convection and field-aligned current by combining data obtained nearly simultaneously both from ground and from space. Therefore, unlike the statistical patterns, the 'snapshot' distributions derived by AMIE allow us to examine in more detail the distinctions between field-aligned current systems associated with separate magnetospheric processes, especially in the dayside cusp region. By comparing the field-aligned current and ionospheric convection patterns with the corresponding spectrograms of precipitating particles, the following signatures have been identified: (1) For the three cases studied, which all had an IMF with negative y and z components, the cusp precipitation was encountered by the DMSP satellites in the postnoon sector in the northern hemisphere and in the prenoon sector in the southern hemisphere. The equatorward part of the cusp in both hemispheres is in the sunward flow region and marks the beginning of the flow rotation from sunward to antisunward. (2) The pair of field-aligned currents near local noon, i.e., the cusp/mantle currents, are coincident with the cusp or mantle particle precipitation. In distinction, the field-aligned currents on the dawnside and duskside, i.e., the normal region 1 currents, are usually associated with the plasma sheet particle precipitation. Thus the cusp/mantle currents are generated on open field lines and the region 1 currents mainly on closed field lines. (3) Topologically, the cusp/mantle currents appear as an expansion of the region 1 currents from the dawnside and duskside and they overlap near local noon. When B(sub y) is negative, in the northern hemisphere the downward field-aligned current is located poleward of the upward current; whereas in the southern hemisphere the upward current is located poleward of the downward current. (4) Under the assumption of quasi-steady state reconnection, the location of the separatrix in the ionosphere is estimated and the reconnection velocity is calculated to be between 400 and 550 m/s. The dayside separatrix lies equatorward of the dayside convection throat in the two cases examined.

Lu, G.↗
NASA NTRS2002

Long-term Doppler Shift and Line Profile Studies of Planetary Search Target Stars

This grant supported attempts to develop a method for measuring the Doppler shifts of solar-type stars more accurately. The expense of future space borne telescopes to search for solar systems like our own makes it worth trying to improve the relatively inexpensive pre-flight reconnaissance by ground-based telescopes. The concepts developed under this grant contributed to the groundwork for such improvements. They were focused on how to distinguish between extrasolar planets and stellar activity (convection) cycles. To measure the Doppler shift (radial velocity; RV) of the center of mass of a star in the presence of changing convection in the star's photosphere, one can either measure the effect of convection separately from that of the star's motion and subtract its contribution to the apparent RV, or measure the RV in a way that is insensitive to convection. This grant supported investigations into both of these approaches. We explored the use of a Fabry-Perot Etalon HE interferometer and a multichannel Fourier Transform Spectrometer (mFTS), and finished making a 1.8-m telescope operational and potentially available for this work.

McMillan, Robert S.↗
DOE OSTI2023

Comparison of free vortex wake and blade element momentum results against large-eddy simulation results for highly flexible turbines under challenging inflow conditions

Abstract. Throughout wind energy development, there has been a push to increase wind turbine size due to the substantial economic benefits. However, increasing turbine size presents several challenges, both physically and computationally. Modeling large, highly flexible wind turbines requires highly accurate models to capture the complicated aeroelastic response due to large deflections and nonstraight blade geometries. Additionally, the development of floating offshore wind turbines requires modeling techniques that can predict large rotor and tower motion. Free vortex wake methods model such complex physics while remaining computationally tractable to perform key simulations necessary during the turbine design process. Recently, a free vortex wake model – cOnvecting LAgrangian Filaments (OLAF) – was added to the National Renewable Energy Laboratory's engineering tool OpenFAST to allow for the aerodynamic modeling of highly flexible turbines along with the aero-hydro-servo-elastic response capabilities of OpenFAST. In this work, free vortex wake and low-fidelity blade element momentum (BEM) results are compared to high-fidelity actuator-line computational fluid dynamics simulation results via the Simulator fOr Wind Farm Applications (SOWFA) method for a highly flexible downwind turbine for varying yaw misalignment, shear exponent, and turbulence intensity conditions. Through these comparisons, it was found that for all considered quantities of interest, SOWFA, OLAF, and BEM results compare well for steady inflow conditions with no yaw misalignment. For OLAF results, this strong agreement with the SOWFA results was consistent for all yaw misalignment values. The BEM results, however, deviated significantly more from the SOWFA results with increasing absolute yaw misalignment. Differences between OLAF and BEM results were dominated by the yaw misalignment angle, with varying shear exponent and turbulence intensity leading to more subtle differences. Overall, OLAF results were more consistent than BEM results when compared to SOWFA results under challenging inflow conditions.

17 WIND ENERGY↗
NASA NTRS1978

Diffuse auroral precipitation

The paper summarizes the development of a plausibly coherent view of the self-consistent coupling of convection in the plasma sheet to auroral particle precipitation and the ionosphere. Attention is given to an understanding of the plasma instabilities responsible for diffuse auroral precipitation. The electrostatic ion and electron cyclotron harmonic loss-cone instabilities seem to be the best candidates, although they depend sensitively upon the cold electron density and temperature deep in space on auroral field lines. However, there is little or no experimental or theoretical information about these parameters. For this reason, further theoretical progress on cyclotron harmonic instabilities will be limited until the cold electron temperature is known. Also necessary are a complete phenomenological understanding of ion harmonic modes and a modeling of the cold electron distribution on auroral field lines.

Ashour-Abdalla, M.↗
NASA NTRS1981

Evidence for chromospheres and coronae in stars - Recent observations, some unanswered theoretical questions, and a speculative scenario

The paper discusses recent UV and X-ray evidence for the existence of solar-type chromospheres, transition regions and coronae in stars other than the sun. The stellar spectral types associated with emission lines indicative of chromospheres and transition regions and X-ray fluxes indicative of coronae are examined, and the possibility of chromospheres and transition regions existing in stars hotter or cooler than the late-type stars is considered. The stellar parameters determining the properties of stellar chromospheres, transition regions and coronae are discussed, including varying magnetic fields, stellar rotation and convection zone parameters. A speculative scenario for the source of chromospheres, transition regions and coronae in O, B and A stars, late-type dwarfs, and G-M giants and supergiants is then presented which is based on the predominant role of magnetic fields in the nonradiative heating of outer atmospheres.

Linsky, J. L.↗
NASA NTRSDate not supplied

Numerical Modeling of No Vent Filling of a Cryogenic Tank with Thermo-dynamic Vent System Assisted Injector

This paper presents a multi-node finite volume model of No Vent Filling (NVF) of a cryogenic tank with Thermo-dynamic Vent System (TVS) assisted injector, using the Generalized Fluid System Simulation Program (GFSSP), a general purpose flow network code. NVF tests were conducted in a CRYOgenic Orbital Testbed (CRYOTE) tank which was filled by liquid nitrogen using a TVS assisted injector with vent valve closed during the entire filling process. In TVS assisted injector, the liquid flow splits into two streams: one stream is routed to a Joule-Thomson (J-T) orifice where the flow immediately flashes from liquid to vapor or two phase mixture because the downstream to J-T leg is maintained at vacuum level.; the other stream is injected into the tank after being cooled by cold vapor of J-T leg in a heat exchanger. The flow through J-T leg is also used to cool the outer metal matrix of the injector which in turn cools the vapor in the tank ullage. The cooling of vapor in the ullage by cold injector surface reduces ullage pressure that allows liquid to enter and fill the tank. An integrated numerical model of the test set up was developed. The model included the dual lines of TVS assisted injector, tank and tank wall. The tank was discretized into multiple fluid nodes and branches to represent the ullage and liquid nitrogen and multiple solid nodes to represent the tank wall and structure. The heat transfer between solid to fluid was calculated from pool boiling correlations which include film, transition, and nucleate boiling, as well as natural convection during pre- and post-boiling. The model also accounts for the condensation of vapor at ullage-injector interface and when it comes in contact with the liquid spray. The predicted pressure, resident mass, wall temperature in the tank were compared with the test data.

Alok Majumdar↗
NASA NTRS2016

IN31A-1734 Development and Evaluation of a Gridded CrIS/ATMS Visualization for Operational Forecasting

A collaborative effort between SPoRT, CIMSS, CIRA, GINA, and NOAA has produced a unique gridded visualization of real-time CrIS/ATMS sounding products. This product uses the NUCAPS retrieval algorithm and polar2grid software to generate plan-view and cross-section visualization for forecast challenges associated with cold air aloft and convective potential. Forecasters at select partner offices have been able to view the Gridded NUCAPS products in AWIPS alongside other operational data products with generally favorable feedback.

aviation↗
NASA NTRS1973

Geysering inhibitor for vertical cryogenic transfer piping

Geysering (i.e., the expulsion of boiling liquid and its vapor from a vertical tube) has been a problem for the missile industry in long vertical cryogenic propellant feed lines connecting the launch vehicle propellant tank with the rocket engines. A proposed novel method of inhibiting geysering and the associated pressure gradients provides a self-starting self-regulating action that is not dependent on other active systems or components. The inhibiting action is attained by incorporating a concentric tube within the main transfer tube to prevent constriction of natural convective flow.

Howard, F. S.↗
NASA NTRS1980

Al-26 from red giants

Simplified models of thermally pulsing red giants are investigated, with particular emphasis on predicting the extent to which nuclear processing at the base of the convective envelope in conjunction with processing in the thermally unstable He shell can synthesize Al-26 (tau/1/2/ = 7.2 x 10 to the 5th yr). Values of Al-26/Al-27 of about 0.5-1, with Al-27/Al-27(solar) of about 1-2, are predicted in some cases. It is pointed out that such results can lead to isotope shifts in the absorption lines of AlH and AlO, which should be observationally identifiable in some late-type supergiants. The possible connection with the anomalous Mg-26 content (assigned to the decay of Al-26) detected in some meteorites and the connection with formation of the solar system are also touched on.

Norgaard, H.↗
NASA NTRS1984

A study of the dependence of Mg II emission on the rotational periods of main-sequence stars

International Ultraviolet Explorer satellite measurements of the Mg II chromospheric emission from a sample of late-type dwarfs with known rotational periods are presented. The ratio of chromospheric to photospheric luminosity for the late-G and K type stars in this sample can be fitted within the probable errors by a single function of rotational period. The chromospheric emission of early-G and F dwarfs appears to depend upon rotation in a qualitatively different way, which suggests that the rapid variation of convective zone properties in this spectral range affects the dissipation of energy in the chromosphere. Mg II h and k emission correlates fairly well with Ca II emission. However, the data sample is not large enough at present to show conclusively that Mg II emission exhibits precisely the same dependence on rotation and spectral type as the Ca II H and K line fluxes.

Hartmann, L.↗
NASA NTRS1986

Parallel acceleration and transport of ions from polar ionosphere to plasma sheet

The effect of the convection electric field in accelerating ions that escape from the polar ionosphere is investigated. It is shown that at high altitudes the velocity component of the ions along the magnetic field may be increased by more than an order of magnitude. The highest velocities are acquired by ions that escape from the region of the ionosphere that is connected along magnetic field lines to the dayside cusps. During disturbed times, ions from that region intercept the center plane of the magnetotail in one to two hours at radial distances exceeding about 6 earth radii. Investigation of the resulting O(+) properties in the center plane, viz., their locations, number densities, and energies, indicates that the polar ionosphere near the cusps is the principal source of the O(+) observed in the plasma sheet. Moreover, a study of the ion motion at quiet and disturbed times indicates that the increase of O(+) in the plasma sheet with increasing AE values (Lennartsson and Shelley, 1986) is due mainly to an increase in the source of O(+) rather than alteration of its transport path.

Cladis, J. B.↗
NASA NTRS2011

Comparative Examination of Plasmoid Ejection at Mercury, Earth, Jupiter, and Saturn

The onset of magnetic reconnection in the near-tail of Earth, long known to herald the fast magnetospheric convection that leads to geomagnetic storms and substorms, is very closely associated with the formation and down-tail ejection of magnetic loops or flux ropes called plasmoids. Plasmoids form as a result of the fragmentation of preexisting cross-tail current sheet as a result of magnetic reconnection. Depending upon the number, location, and intensity of the individual reconnection X-lines and how they evolve, some of these loop-like or helical magnetic structures may also be carried sunward. At the inner edge of the tail they are expected to "re-reconnect' with the planetary magnetic field and dissipate. Plasmoid ejection has now been observed in the magnetotails of Mercury, Earth, Jupiter, and Saturn. These magnetic field and charged particle measurements have been taken by the MESSENGER, Voyager, Galileo, Cassini, and numerous Earth missions. Here we present a comparative examination of the structure and dynamics of plasmoids observed in the magnetotails of these 5 planets. The results are used to learn more about how these magnetic structures form and to assess similarities and differences in the nature of magnetotail reconnection at these planets.

Slavin, James A.↗
NASA NTRS2021

Time Resolved Particle Image Velocimetry in Nozzle Flow

Temporally resolved particle image velocimetry (TR-PIV) is the newest and most exciting tool recently developed to support our continuing efforts to characterize and improve our understanding of the decay of turbulence in jet flows—a critical element for understanding the acoustic properties of the flow. A new TR-PIV system has been developed at the NASA Glenn Research Center which is capable of acquiring planar PIV image frame pairs at up to 25 kHz. The data reported here were collected at Mach numbers of 0.5 and 0.9 and at temperature ratios of 0.89 and 1.76. The field of view of the TR-PIV system covered six nozzle diameters along the lip line of the 50.8 mm diameter jet. The cold flow data at Mach 0.5 were compared with hotwire anemometry measurements in order to validate the new TR-PIV technique. The axial turbulence profiles measured across the shear layer using TR-PIV were thinner than those measured using hotwire anemometry and remained centred along the nozzle lip line. The collected TR-PIV data illustrate the differences in the single point statistical flow properties of cold and hot jet flows. The planar, time-resolved velocity records were then used to compute two-point space–time correlations of the flow at the Mach 0.9 flow condition. The TR-PIV results show that there are differences in the convective velocity and growth rate of the turbulent structures between cold and hot flows at the same Mach number.

Temporally Resolved Particle Image Velocimetry↗
NASA NTRS2021

Effect of volcanic emissions on clouds during the 2008 and 2018 Kilauea degassing events

Volcanic eruptions in otherwise clean environments are “natural experiments” wherein the effects of aerosol emissions on clouds and climate can be partitioned from meteorological variability and anthropogenic activities. In this work, we combined satellite retrievals, reanalysis products, and atmospheric modeling to analyze the mechanisms of aerosol–cloud interactions during two degassing events at the Kilauea volcano in 2008 and 2018. The eruptive nature of the 2008 and 2018 degassing events was distinct from long-term volcanic activity for Kilauea. Although previous studies assessed the modulation of cloud properties from the 2008 event, this is the first time such an analysis has been reported for the 2018 event and that multiple degassing events have been analyzed and compared at this location. Both events resulted in significant changes in cloud effective radius and cloud droplet number concentration that were decoupled from local meteorology and in line with an enhanced cloud albedo. However, it is likely that the effects of volcanic emissions on liquid water path and cloud fraction were largely offset by meteorological variability. Comparison of cloud anomalies between the two events suggested a threshold response of aerosol–cloud interactions to overcome meteorological effects, largely controlled by aerosol loading. In both events, the ingestion of aerosols within convective parcels enhanced the detrainment of condensate in the upper troposphere, resulting in deeper clouds than observed under pristine conditions. Accounting for ice nucleation on ash particles led to enhanced ice crystal concentrations at cirrus levels and a slight decrease in ice water content, improving the correlation of the model results with the satellite retrievals. Overall, aerosol loading, plume characteristics, and meteorology contributed to changes in cloud properties during the Kilauea degassing events.

Katherine H. Breen↗
NASA NTRS1992

Viscosity and thermal fields associated with strongly chaotic non-Newtonian thermal convection

The thermomechanical structure is investigated in strongly chaotic non-Newtonian thermal convection for both base-heated and internally-heated systems. Temperature can build up in stagnant regions and a non-Newtonian mantle can tolerate less internal heating. Viscosity fields of the strongly chaotic regime show a granular structure. The horizontal spectra of viscosity fluctuations obey a power-law and yield a fractal dimension of 1.6 to 1.8 for the isoviscosity lines, providing evidence for 2D turbulence. Long-wavelength viscosity variations are smoothed out by the turbulent non-Newtonian flows.

Malevsky, A. V.↗
NASA NTRS1993

Observation of 3-6 day meridional wind oscillations over the tropical Pacific, 1973-1992: Vertical structure and interannual variability

Rawinsonde data from tropical Pacific stations were examined for westward-propagating 3-6-day meridional wind oscillations in the troposphere and lower stratosphere, 1973-1992. Four types were identified from cross-spectrum and principal component analysis. (1) The dominant oscillation, near 250 mb, had a period slightly greater than 5 days, zonal wavenumber 4-6, and modified Rossby-gravity structure near the date line. (2) In the western Pacific lower troposphere there was broadband activity with short zonal scale, coupled to upper-tropospheric waves in NH summer. (3) In the central Pacific, during NH autumn, there was a well-defined approximately 4 1/2-day oscillation with maximum amplitude in the lower troposphere and baroclinic phase tilt above. The vertical structure suggested coupling to deep tropical convection; this interpretation was supported by correlation of meridional wind with antisymmetric outgoing longwave radiation. (4) In the stratosphere, Rossby-gravity waves had periods less than or equal to 4 days and zonal wavenumber 3-4. Unlike tropospheric waves, these disturbances were coherent in a shallow layer, largest in west phase of quasi-biennial oscillation (QBO) and annual cycle (NH winter-spring).

Dunkerton, Timothy J.↗
NASA NTRS2002

Origin of Magnetic Lineations on Mars

The magnetic lineations discovered by MGS (Mars Global Surveyor) have been considered to be evidence of early plate tectonics on Mars. However, the lineations approximately follow lines of latitude, i.e., small circles. This presents significant geometrical problems for plate-like spreading, particularly at high latitudes. However, the sublatitudinal orientation of the lineations is consistent with meridianal extension and perhaps limited crustal spreading due to a stress event centered near the geographic pole. We hypothesize that this event was the early formation of the crustal dichotomy through mantle-convective processes. This could have taken the form of a southern megaplume that formed the thick highlands crust or as subduction or downwelling in the north. Both would result in tensional stresses in the south that would form extensional fractures perpendicular to the CM-CF (center-of-mass/center-of-gravity) offset. The observed magnitude and distribution of magnetization indicates that crustal intrusion associated with this major mantle-convective event resulted in approximately 1000 km of extension in the Southern highlands. Subsequent spin-axis reorientation due to loss of crust in the north or gain of crust in the south brought the CM-CF offset into its present N-S alignment. A portion of the ancient valley networks observed in the southern highlands are spatially associated with crustal magnetism and are quantitatively shown to be consistent with hydrothermal discharge over crustal intrusions.

Grimm, Robert E.↗