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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 1,441 records · Page 80
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Analysis of coronal H I Lyman alpha measurements from a rocket flight on 1979 April 13

It is noted that measurements of the profiles of resonantly scattered hydrogen Lyman-alpha coronal radiation have been used in determining hydrogen kinetic temperatures from 1.5 to 4 solar radii from sun center in a quiet region of the corona. Proton temperatures derived using the line widths decrease with height from 2.6 x 10 to the 6th K at 1.5 solar radii to 1.2 x 10 to the 6th K at 4 solar radii. These measurements, together with temperatures for lower heights determined from earlier Skylab and eclipse data, suggest that there is a maximum in the quiet coronal proton temperature at about 1.5 solar radii. Comparison of measured Lyman-alpha intensities with those calculated using a representative model for the radial variation of the coronal electron density yields information on the magnitude of the electron temperature gradient and suggests that the solar wind flow was subsonic for distances less than 4 solar radii.

Withbroe, G. L.↗
NASA NTRS1986

Photochemical damping of inertio-gravity waves

A simple model is developed for the coupling effect of radiative heating and ozone photochemistry on inertio-gravity waves in the region 16-70 km. It is found that the photochemical damping rate is the weighted sum of the rates caused by two individual processes. One, suggested by Craig and Ohring, involves the temperature dependence of ozone reaction rate coefficients; the other, suggested by Leovy, involves the vertical gradient of the ozone mixing ratio. The relative importance of these two processes depends on the ratio of dynamical and chemical relaxation times. Calculations show that the most important region for coupling is near 48 km where the total relaxation time is 8 days for equinox and 6 days for summer midlatitude.

Zhu, Xun↗
NASA NTRS1988

Explicit upwind algorithm for the parabolized Navier-Stokes equations

A new explicit upwind algorithm based on Roe's flux-difference splitting (FDS) method has been developed for the three-dimensional Parabolized Navier-Stokes (PNS) equations. For three-dimensional flows, FDS's are determined separately for the two nonmarching directions and modified to account for the calculated shock angle in the crossflow plane. Second-order FDS is applied to the pressure and convection terms with the streamwise pressure gradient limited in the subsonic region to maintain a hyperbolic inviscid equation set. Second-order central differencing is obtained in the two-step algorithm for the shear and heat flux terms. The new algorithm is demonstrated for three laminar flow test cases: supersonic flow over a flat plate, hypersonic flow over a 15 deg ramp, and hypersonic flow past a 10 deg cone at a 24 deg angle of attack. The computed results agree well with experimental measurements.

Korte, John J.↗
NASA NTRS1996

ATMOS/ATLAS-3 Observations of Long-Lived Tracers and Descent in the Antarctic Vortex in November 1994

Observations of the long-lived tracers N2O, CH4 and HF obtained by the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument in early November 1994 are used to estimate average descent rates during winter in the Antarctic polar vortex of 0.5 to 1.5 km/month in the lower stratosphere, and 2.5 to 3.5 km/month in the middle and upper stratosphere. Descent rates inferred from ATMOS tracer observations agree well with theoretical estimates obtained using radiative heating calculations. Air of mesospheric origin (N2O less than 5 ppbV) was observed at altitudes above about 25 km within the vortex. Strong horizontal gradients of tracer mixing ratios, the presence of mesospheric air in the vortex in early spring, and the variation with altitude of inferred descent rates indicate that the Antarctic vortex is highly isolated from midlatitudes throughout the winter from approximately 20 km to the stratopause. The 1994 Antarctic vortex remained well isolated between 20 and 30 km through at least mid-November.

Abrams, M. C.↗
NASA NTRS1997

An Experimental Study of a Radially Arranged Thin Film Heat Flux Gauge

A new thin-film heat-flux gauge was designed and fabricated on three different substrate materials. Forty pairs of Pt-Pt/10% Rh thermocouple junctions were deposited in a circular pattern on the same plane of the substrate. Over the thermocouples, 5 and 10 micron thick thermal resistance layers were deposited to create a temperature gradient across those layers. Calibration and testing of these gauges were carried out in an arc-lamp calibration facility. The heat flux calculated from the gauge output is in good agreement with the value obtained from the pre-calibrated standard sensor. A CO2 laser was also used to test the steady-state and dynamic responses of the heat-flux gauge. During the steady-state test, the time constant for the heating period was 30 s. The frequency response of the heat-flux gauge was measured in the frequency domain using a CO2 laser and a chopper. The responses from an infrared detector and the heat-flux gauge were measured simultaneously and compared. It was found that the thin-film heat-flux gauge has a dynamic frequency response of 3 kHz.

Cho, Christoper S. K.↗
NASA NTRS2007

Experimental Evaluation of an Isolated Synthetic Jet IN Crossflow

The second case for this workshop builds upon the isolated synthetic jet of Case 1 by adding a crossflow, with no streamwise pressure gradient, for the developing jet to interact with. Formally, Case 2 examines the interaction of a single, isolated, synthetic jet and a fully turbulent zero-pressure gradient boundary layer. The resulting flow has many of the characteristics that need to be modeled with fidelity if the results of the calculations are to serve as the basis for research and design with active flow control devices. These include the turbulence in the boundary layer, the time-evolution of the large vortical structure emanating from the jet orifice and its subsequent interaction with and distortion by the boundary layer turbulence, and the effect of the suction cycle on the boundary layer flow. In a synthetic jet, the flow through the orifice and out into the outer flowfield alternates between an exhaust and a suction cycle, driven by the contraction and expansion of a cavity internal to the actuator. In the present experiment, the volume changes in the internal cavity are accomplished by replacing one of the rigid walls of the cavity, the wall opposite the orifice exit, with a deformable wall. This flexible wall is driven by a bottom-mounted moveable piston. The piston is driven electro-mechanically. The synthetic jet issues into the external flow through a circular orifice. In the present experiment, this orifice has a diameter of 0.250 inches (6.35 mm). The flow is conceptually similar to that documented in Schaeffler [1]. To document the flow, several measurement techniques were utilized. The upstream boundary conditions (in-flow conditions), and several key phase-averaged velocity profiles were measured with a 3-component laser-Doppler velocimetry system. Phase-averaged velocity field measurements were made with both stereo digital particle image velocimetry and 2-D digital particle image velocimetry as the primary measurement system. Surface pressure measurements were made utilizing an electronically scanned pressure system.

Schaeffler, Norman W.↗
NASA NTRS1990

Comparisons of a Three-Dimensional, Full Navier Stokes Computer Model with High Mach Number Combuster Test Data

Comparisons between scramjet combustor data and a three-dimensional full Navier-Stokes calculation have been made to verify and substantiate computational fluid dynamics (CFD) codes and application procedures. High Mach number scramjet combustor development will rely heavily on CFD applications to provide wind tunnel-equivalent data of quality sufficient to design, build and fly hypersonic aircraft. Therefore. detailed comparisons between CFD results and test data are imperative. An experimental case is presented, for which combustor wall static pressures were measured and flow-fieid interferograms were obtained. A computer model was done of the experiment, and counterpart parameters are compared with experiment. The experiment involved a subscale combustor designed and fabricated for the National Aero-Space Plane Program, and tested in the Calspan Corporation 96" hypersonic shock tunnel. The combustor inlet ramp was inclined at a 20 angle to the shock tunnel nozzle axis, and resulting combustor entrance flow conditions simulated freestream M=10. The combustor body and cowl walls were instrumented with static pressure transducers, and the combustor lateral walls contained windows through which flowfield holographic interferograms were obtained. The CFD calculation involved a three-dimensional time-averaged full Navier-Stokes code applied to the axial flow segment containing fuel injection and combustion. The full Navier-Stokes approach allowed for mixed supersonic and subsonic flow, downstream-upstream communication in subsonic flow regions, and effects of adverse pressure gradients. The code included hydrogen-air chemistry in the combustor segment which begins near fuel injection and continues through combustor exhaust. Combustor ramp and inlet segments on the combustor lateral centerline were modelled as two dimensional. Comparisons to be shown include calculated versus measured wall static pressures as functions of axial flow coordinate, and calculated path-averaged density contours versus an holographic Interferogram.

Watkins, William B.↗
DOE OSTI2022

Ion thermal transport in the H-mode edge transport barrier on DIII-D

The power balance ion heat flux in the pedestal region on DIII-D increases and becomes increasingly anomalous (above conventional neoclassical) in experiments with higher temperature and lower density pedestals where the ion collisionality ($v^*_i$) is lowered toward values expected on ITER. Direct measurements of the main-ion temperature are shown to be essential on DIII-D when calculating the ion heat flux due to differences between the temperature of $D^+$ and the more commonly measured $C^{6+}$ impurity ions approaching the separatrix. Neoclassical transport calculations from NEO and non-linear gyrokinetic calculations using CGYRO are consistent with these observations and show that while neoclassical transport plays an important role, the turbulent ion heat flux due to ion scale electrostatic turbulence is significant and can contribute similar or larger ion heat fluxes at lower collisionality. Beam emission spectroscopy and Doppler backscattering measurements in the steep gradient region of the H-mode pedestal reveal increased broadband, long-wavelength ion scale fluctuations for the low $v^*_i$ discharges at the radius where the non-linear CGYRO simulations were run. Taken together, increased fluctuations, power balance calculations, and gyrokinetic simulations show that the above neoclassical ion heat fluxes, including the increases at lower $v^*_i$, are likely due to weakly suppressed ion scale electrostatic turbulence. These new results are based on world first inferred ion and electron heat fluxes in the pedestal region of deuterium plasmas using direct measurements of the deuterium temperature for power balance across ion collisionalities covering an order of magnitude from high $v^*_i$ values of 1.3 down to ITER relevant $v^*_i$ ~0.1.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Ab initio studies of structural, electronic, optical, elastic and thermal properties of silver gallium dichalcogenides (AgGaX{sub 2}: X = S, Se, Te)

Graphical abstract: - Highlights: • FP-LAPW method has been used to compute the solid state properties of AgGaX{sub 2} (X = S, Se, Te). • Electronic and optical properties reported with recently developed mBJ potential. • Thermal expansion, heat capacity, Debye temperature, entropy and Grüneisen parameter were evaluated. • Hardness was calculated for the first time at different temperature and pressure. - Abstract: We have performed ab initio calculations for the structural, electronic, optical, elastic and thermal properties of the silver gallium dichalcogenides (AgGaX{sub 2}: X = S, Se, Te). In this study, we have used the accurate full potential linearized augmented plane wave (FP-LAPW) method to find the equilibrium structural parameters and to compute the six elastic constants (C{sub 11}, C{sub 12}, C{sub 13}, C{sub 33}, C{sub 44} and C{sub 66}). We have reported electronic and optical properties with the recently developed density functional theory of Tran and Blaha, and this theory is used along with the Wu-Cohen generalized gradient approximation (WC-GGA) for the exchange-correlation potential. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients and optical conductivities were calculated for photon energies up to 40 eV. The thermodynamical properties such as thermal expansion, heat capacity, debye temperature, entropy, Grüneisen parameter and bulk modulus were calculated employing the quasi-harmonic Debye model at different temperatures (0–900 K) and pressures (0–8 GPa) and the silent results were interpreted. Hardness of the materials was calculated for the first time at different temperatures and pressures.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Structural, electronic and thermodynamic properties of R{sub 3}ZnH{sub 5} (R=K, Rb, Cs): A first-principle calculation

R{sub 3}ZnH{sub 5} (R=K, Rb, Cs) series have been investigated with respect to the crystal structure, electronic and thermodynamic properties using first-principle methods based on density functional theory with generalized gradient approximation. The optimized structures and atomic coordinates are in good agreement with the experimental data. The strong covalent interactions are obtained between Zn and H atoms in the 18-electron [ZnH{sub 4}]{sup 2-} complex, while an ionic interaction is found between [ZnH{sub 4}]{sup 2-} and R atom. The formation enthalpies show that the formations of R{sub 3}ZnH{sub 5} hydrides are all exothermic at 298 K. The vibration free energies of R{sub 3}ZnH{sub 5} show that the thermodynamic stabilities of R{sub 3}ZnH{sub 5} hydrides decrease with the increasing diameter of R atom. Two possible decomposition reactions of R{sub 3}ZnH{sub 5} series have been suggested in our work. One (reaction one) is that R{sub 3}ZnH{sub 5} hydrides decomposes to elements directly, and the other (reaction two) is that R{sub 3}ZnH{sub 5} hydrides decomposes to RH hydride. The results show that the first decomposition reaction is more favorable one. The spontaneous decomposition reaction of K{sub 3}ZnH{sub 5} hydrides occur upon 465 K via reaction one, and 564 K via reaction two, respectively. - Graphical abstract: Total charge density of K{sub 3}ZnH{sub 5}. Highlights: Black-Right-Pointing-Pointer Electronic and thermodynamic properties of R{sub 3}ZnH{sub 5} (R=K, Rb, Cs) were calculated. Black-Right-Pointing-Pointer The formations of R{sub 3}ZnH{sub 5} hydrides are all exothermic at 298 K. Black-Right-Pointing-Pointer The thermodynamic stabilities decrease with the increasing diameter of R atom. Black-Right-Pointing-Pointer Two possible decomposition pathways of R{sub 3}ZnH{sub 5} were investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Examination of How Well Long-Range-Corrected Density Functionals Satisfy the Ionization Energy Theorem

For this work, we calculated the vertical ionization energies (VIE) of 99 species in two ways to examine the accuracy of several long-range-corrected (LC) hybrid meta functionals in comparison with a gradient approximation (GA), global hybrids, and doubly hybrids. In the category of LC functionals, we examined both those with meta ingredients (i.e., that depend on the kinetic energy density) and those without them. The LC-hybrid meta functionals examined are M11, revM11, M11plus, and ωB97M-V. The reference data used to assess accuracy consist of 95 molecules and 4 atoms in the GW100 set. The two methods studied are the ΔSCF method (involving the difference of neutral and cation self-consistent field (SCF) energies) and the ionization energy theorem (involving the orbital energy of the highest occupied molecular orbital, HOMO). We calculated linear correlation coefficients (r 2 ) and mean absolute deviations (MADs) between each approach and the reference VIE value from the CCSD(T)/def2-TZVPP level of theory. We compared the new LC-hybrid meta calculations to calculations with the 10 functionals in a previous VIE study by Brémond et al. and to the calculations with LC-BLYP (LC-Becke, Lee–Yang–Parr), CAM-B3LYP (Coulomb-attenuating-method Becke-3-parameter Lee–Yang–Parr), LC-ωHPBE, and ωB97X-D. The results show that Minnesota LC-hybrid meta functionals have the smallest mean absolute deviation of ionization energy theorem VIEs with the reference data; the LC-ωHPBE functional also does quite well in this test. This is very encouraging and indicates that LC-hybrid meta functionals would be the best starting points for the tuning strategy that has been shown to be a very good procedure for improving time-dependent density functional calculations, and it also helps explain the good success of LC-hybrid meta functionals for molecular excitation energies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Re-examining the silicon self-interstitial charge states and defect levels: A density functional theory and bounds analysis study

The self-interstitial atom (SIA) is one of two fundamental point defects in bulk Si. Isolated Si SIAs are extremely difficult to observe experimentally. Even at very low temperatures, they anneal before typical experiments can be performed. Given the challenges associated with experimental characterization, accurate theoretical calculations provide valuable information necessary to elucidate the properties of these defects. Previous studies have applied Kohn–Sham density functional theory (DFT) to the Si SIA, using either the local density approximation or the generalized gradient approximation to the exchange-correlation (XC) energy. The consensus of these studies indicates that a Si SIA may exist in five charge states ranging from -2 to +2 with the defect structure being dependent on the charge state. This study aims to re-examine the existence of these charge states in light of recently derived “approximate bounds” on the defect levels obtained from finite-size supercell calculations and new DFT calculations using both semi-local and hybrid XC approximations. We conclude that only the neutral and +2 charge states are directly supported by DFT as localized charge states of the Si SIA. Within the current accuracy of DFT, our results indicate that the +1 charge state likely consists of an electron in a conduction-band-like state that is coulombically bound to a +2 SIA. Furthermore, the -1 and -2 charge states likely consist of a neutral SIA with one and two additional electrons in the conduction band, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Optical response and band structure of LiCoO 2 including electron-hole interaction effects

The optical response functions and band structures of LiCoO 2 are studied at different levels of approximation, from density functional theory (DFT) in the generalized gradient approximation (GGA) to quasiparticle self-consistent QSGW (with G for Green's function and W for screened Coulomb interaction) without and with ladder diagrams ($QSG\hat{W}$) and the Bethe Salpeter Equation (BSE) approach. The QSGW method is found to strongly overestimate the band gap and electron-hole or excitonic effects are found to be important. They lower the quasiparticle gap by only about 11~\% but the lowest energy peaks in absorption are found to be excitonic in nature. The contributions from different band to band transitions and the relation of excitons to band-to-band transitions are analyzed. Finally, the excitons are found to be strongly localized. Finally, a comparison to experimental data is presented.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Accurate adiabatic singlet-triplet gaps in atoms and molecules employing the third-order spin-flip algebraic diagrammatic construction scheme for the polarization propagator

For the calculation of adiabatic singlet-triplet gaps (STG) in diradicaloid systems the spin-flip (SF) variant of the algebraic diagrammatic construction (ADC) scheme for the polarization propagator in third order perturbation theory (SF-ADC(3)) has been applied. Due to the methodology of the SF approach the singlet and triplet states are treated on an equal footing since they are part of the same determinant subspace. This leads to a systematically more accurate description of, e.g., diradicaloid systems than with the corresponding non-SF single-reference methods. Furthermore, using analytical excited state gradients at ADC(3) level, geometry optimizations of the singlet and triplet states were performed leading to a fully consistent description of the systems, leading to only small errors in the calculated STGs ranging between 0.6 and 2.4 kcal/mol with respect to experimental references.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Gaussian integral method for void fraction

Here, a novel method, the Gaussian Integral Method (GIM), is presented for calculating void fractions in Computational Fluid Dynamics–Discrete Element Method (CFD-DEM) simulations. GIM is versatile and applicable to various grid types, including structured and unstructured polyhedral meshes, without requiring special boundary treatments. An optimization technique is introduced to make GIM independent of grid resolution and type. The method is validated against experimental data from a fluidized bed, demonstrating that GIM produces realistic simulations closely resembling experimental observations. Additionally, unstructured polyhedral grids using GIM outperform structured grids of equivalent resolution, yielding results more aligned with experimental data. The gradient of the void fraction is computed in the CFD solver and utilized in the DEM solver for precise estimation at particle locations. Overall, GIM provides an effective solution for void fraction calculations in particulate media simulations with complex geometries, enhancing the accuracy and applicability of CFD-DEM simulations for industrial processes.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2016

MAIN SEQUENCE EVOLUTION WITH LAYERED SEMICONVECTION

Semiconvection is a form of mixing in thermally unstable regions that are partially stabilized by composition gradients. It has the greatest potential impact on the evolution of the cores of main sequence stars in the mass range 1.2 M{sub ⊙}–1.7 M{sub ⊙}. We present the first stellar evolution calculations using the new prescription for semiconvective mixing proposed by Wood et al. Semiconvection in stars is predominately layered semiconvection. In our model, the layer height is an adjustable parameter analogous to the mixing length in convection. The rate of mixing inside semiconvective regions is sensitively dependent on the layer height. We find a critical layer height that separates weak semiconvective mixing (where stellar evolution is well-approximated by ignoring semiconvection entirely and using the Ledoux criterion for convection) from strong semiconvective mixing (where all composition gradients are rapidly mixed, so stellar evolution is well-approximated by ignoring them altogether and using the Schwarzschild criterion for convection instead). This critical layer height is much smaller than the minimum layer height derived from simulations so we predict that stellar evolution is nearly the same as in models ran with the Schwarzschild criterion. We also investigate the effects of composition gradient smoothing, finding that it causes convective cores to artificially shrink in the absence of additional mixing beyond the convective boundary. Layered semiconvection with realistic layer heights provides enough such mixing to avoid this problem. Finally, we discuss the potential of detecting layered semiconvection and its implication on convective core sizes in solar-like oscillators.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2002

Localized Gravity/Topography Admittance and Correlation Spectra on Mars: Implications for Regional and Global Evolution

[i] From gravity and topography data collected by the Mars Global Surveyor spacecraft we calculate gravity/topography admittances and correlations in the spectral domain and compare them to those predicted from models of lithospheric flexure. On the basis of these comparisons we estimate the thickness of the Martian elastic lithosphere (T(sub e)) required to support the observed topographic load since the time of loading. We convert T(sub e) to estimates of heat flux and thermal gradient in the lithosphere through a consideration of the response of an elastic/plastic shell. In regions of high topography on Mars (e.g., the Tharsis rise and associated shield volcanoes), the mass-sheet (small-amplitude) approximation for the calculation of gravity from topography is inadequate. A correction that accounts for finite-amplitude topography tends to increase the amplitude of the predicted gravity signal at spacecraft altitudes. Proper implementation of this correction requires the use of radii from the center of mass (collectively known as the planetary shape ) in lieu of topography referenced to a gravitational equipotential. Anomalously dense surface layers or buried excess masses are not required to explain the observed admittances for the Tharsis Montes or Olympus Mons volcanoes when this correction is applied. Derived T, values generally decrease with increasing age of the lithospheric load, in a manner consistent with a rapid decline of mantle heat flux during the Noachian and more modest rates of decline during subsequent epochs.

McGovern, Patrick J.↗
DOE OSTI2015

Giant enhancement in the ferroelectric field effect using a polarization gradient

Coupling of switchable ferroelectric polarization with the carrier transport in an adjacent semiconductor enables a robust, non-volatile manipulation of the conductance in a host of low-dimensional systems, including the two-dimensional electron liquid that forms at the LaAlO{sub 3} (LAO)-SrTiO{sub 3} (STO) interface. However, strength of the gate-channel coupling is relatively weak, limited in part by the electrostatic potential difference across a ferroelectric gate. Here, through application of phenomenological Landau-Ginzburg-Devonshire theory and self-consistent Poisson-Schrödinger model calculations, we show how compositional grading of PbZr{sub 1−x}Ti{sub x}O{sub 3} ferroelectric gates enables a more than twenty-five-fold increase in the LAO/STO channel conductance on/off ratios. Incorporation of polarization gradients in ferroelectric gates can enable breakthrough performance of ferroelectric non-volatile memories.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗