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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Effect of inducer inlet and diffuser throat areas on performance of a low pressure ratio sweptback centrifugal compressor

A low-pressure-ratio centrifugal compressor was tested with nine combinations of three diffuser throat areas and three impeller inducer inlet areas which were 75, 100, and 125 percent of design values. For a given inducer inlet area, increases in diffuser area within the range investigated resulted in increased mass flow and higher peak efficiency. Changes in both diffuser and inducer areas indicated that efficiencies within one point of the maximum efficiency were obtained over a compressor specific speed range of 27 percent. The performance was analyzed of an assumed two-spool open-cycle engine using the 75 percent area inducer with a variable area diffuser.

Klassen, H. A.↗
DOE OSTI2014

Low dose dynamic CT myocardial perfusion imaging using a statistical iterative reconstruction method

Purpose: Dynamic CT myocardial perfusion imaging has the potential to provide both functional and anatomical information regarding coronary artery stenosis. However, radiation dose can be potentially high due to repeated scanning of the same region. The purpose of this study is to investigate the use of statistical iterative reconstruction to improve parametric maps of myocardial perfusion derived from a low tube current dynamic CT acquisition. Methods: Four pigs underwent high (500 mA) and low (25 mA) dose dynamic CT myocardial perfusion scans with and without coronary occlusion. To delineate the affected myocardial territory, an N-13 ammonia PET perfusion scan was performed for each animal in each occlusion state. Filtered backprojection (FBP) reconstruction was first applied to all CT data sets. Then, a statistical iterative reconstruction (SIR) method was applied to data sets acquired at low dose. Image voxel noise was matched between the low dose SIR and high dose FBP reconstructions. CT perfusion maps were compared among the low dose FBP, low dose SIR and high dose FBP reconstructions. Numerical simulations of a dynamic CT scan at high and low dose (20:1 ratio) were performed to quantitatively evaluate SIR and FBP performance in terms of flow map accuracy, precision, dose efficiency, and spatial resolution. Results: Forin vivo studies, the 500 mA FBP maps gave −88.4%, −96.0%, −76.7%, and −65.8% flow change in the occluded anterior region compared to the open-coronary scans (four animals). The percent changes in the 25 mA SIR maps were in good agreement, measuring −94.7%, −81.6%, −84.0%, and −72.2%. The 25 mA FBP maps gave unreliable flow measurements due to streaks caused by photon starvation (percent changes of +137.4%, +71.0%, −11.8%, and −3.5%). Agreement between 25 mA SIR and 500 mA FBP global flow was −9.7%, 8.8%, −3.1%, and 26.4%. The average variability of flow measurements in a nonoccluded region was 16.3%, 24.1%, and 937.9% for the 500 mA FBP, 25 mA SIR, and 25 mA FBP, respectively. In numerical simulations, SIR mitigated streak artifacts in the low dose data and yielded flow maps with mean error <7% and standard deviation <9% of mean, for 30×30 pixel ROIs (12.9 × 12.9 mm{sup 2}). In comparison, low dose FBP flow errors were −38% to +258%, and standard deviation was 6%–93%. Additionally, low dose SIR achieved 4.6 times improvement in flow map CNR{sup 2} per unit input dose compared to low dose FBP. Conclusions: SIR reconstruction can reduce image noise and mitigate streaking artifacts caused by photon starvation in dynamic CT myocardial perfusion data sets acquired at low dose (low tube current), and improve perfusion map quality in comparison to FBP reconstruction at the same dose.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Dose ratio proton radiography using the proximal side of the Bragg peak

Purpose: In recent years, there has been a movement toward single-detector proton radiography, due to its potential ease of implementation within the clinical environment. One such single-detector technique is the dose ratio method in which the dose maps from two pristine Bragg peaks are recorded beyond the patient. To date, this has only been investigated on the distal side of the lower energy Bragg peak, due to the sharp falloff. The authors investigate the limits and applicability of the dose ratio method on the proximal side of the lower energy Bragg peak, which has the potential to allow a much wider range of water-equivalent thicknesses (WET) to be imaged. Comparisons are made with the use of the distal side of the Bragg peak. Methods: Using the analytical approximation for the Bragg peak, the authors generated theoretical dose ratio curves for a range of energy pairs, and then determined how an uncertainty in the dose ratio would translate to a spread in the WET estimate. By defining this spread as the accuracy one could achieve in the WET estimate, the authors were able to generate lookup graphs of the range on the proximal side of the Bragg peak that one could reliably use. These were dependent on the energy pair, noise level in the dose ratio image and the required accuracy in the WET. Using these lookup graphs, the authors investigated the applicability of the technique for a range of patient treatment sites. The authors validated the theoretical approach with experimental measurements using a complementary metal oxide semiconductor active pixel sensor (CMOS APS), by imaging a small sapphire sphere in a high energy proton beam. Results: Provided the noise level in the dose ratio image was 1% or less, a larger spread of WETs could be imaged using the proximal side of the Bragg peak (max 5.31 cm) compared to the distal side (max 2.42 cm). In simulation, it was found that, for a pediatric brain, it is possible to use the technique to image a region with a square field equivalent size of 7.6 cm{sup 2}, for a required accuracy in the WET of 3 mm and a 1% noise level in the dose ratio image. The technique showed limited applicability for other patient sites. The CMOS APS demonstrated a good accuracy, with a root-mean-square-error of 1.6 mm WET. The noise in the measured images was found to be σ = 1.2% (standard deviation) and theoretical predictions with a 1.96σ noise level showed good agreement with the measured errors. Conclusions: After validating the theoretical approach with measurements, the authors have shown that the use of the proximal side of the Bragg peak when performing dose ratio imaging is feasible, and allows for a wider dynamic range than when using the distal side. The dynamic range available increases as the demand on the accuracy of the WET decreases. The technique can only be applied to clinical sites with small maximum WETs such as for pediatric brains.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1978

Effect of flight loads on turbofan engine performance deterioration

A significant percentage of high bypass ratio, turbofan engine performance deterioration was caused by an increase in operating clearance between fan/compressor and turbine blades and their outer air seals. These increased clearances resulted from rubs induced by a combination of engine power transients and aircraft flight loads. An analytical technique for predicting the effect of quasi-steady state aircraft flight loads on engine performance deterioration was developed and is presented. Thrust, aerodynamic and inertia loads were considered. Analytical results are shown and compared to actual engine test experience.

Stakolich, E. G.↗
NASA NTRS1991

Survey of research on unsteady aerodynamic loading of delta wings

For aeronautical applications, there has been recent interest in accurately determining the aerodynamic forces and moments experienced by low-aspect-ratio wings performing transient maneuvers which go to angles of attack as high as 90 deg. Focusing on the delta planform with sharp leading edges, the paper surveys experimental and theoretical investigations dealing with the associated unsteady flow phenomena. For maximum angles above a value between 30 and 40 deg, flow details and airloads are dominated by hysteresis in the 'bursting' instability of intense vortices which emanate from the leading edge. As examples of relevant test results, force and moment histories are presented for a model series with aspect ratios 1, 1.5 and 2. Influences of key parameters are discussed, notably those which measure unsteadiness. Comparisons are given with two theories: a paneling approximation that cannot capture bursting but clarifies other unsteady influences, and a simplified estimation scheme which uses measured bursting data.

Ashley, H.↗
DOE OSTI2021

Achieving record hot spot energies with large HDC implosions on NIF in HYBRID-E

HYBRID-E is an inertial confinement fusion implosion design that increases energy coupled to the hot spot by increasing the capsule scale in cylindrical hohlraums while operating within the current experimental limits of the National Ignition Facility. HYBRID-E reduces the hohlraum scale at a fixed capsule size compared to previous HYBRID designs, thereby increasing the hohlraum efficiency and energy coupled to the capsule, and uses the cross-beam energy transfer (CBET) to control the implosion symmetry by operating the inner (23° and 30°) and outer (44° and 50°) laser beams at different wavelengths (Δλ> 0). Small case to capsule ratio designs can suffer from insufficient drive at the waist of the hohlraum. We show that only a small amount of wavelength separation between the inner and outer beams (Δλ1-2 Å) is required to control the symmetry in low-gas-filled hohlraums (0.3 mg/cm3 He) with enough drive at the waist of the hohlraum to symmetrically drive capsules 1180 μm in outer radius. This campaign is the first to use the CBET to control the symmetry in 0.3 mg/cm3 He-filled hohlraums, the lowest gas fill density yet fielded with Δλ> 0. We find a stronger sensitivity of hot spot P2 in μm per Angstrom (40–50 μm/Å wavelength separation) than observed in high-gas-filled hohlraums and previous longer pulse designs that used a hohlraum gas fill density of 0.6 mg/cm3. There is currently no indication of transfer roll-off with increasing Δλ, indicating that even longer pulses or larger capsules could be driven using the CBET in cylindrical hohlraums. We show that the radiation flux symmetry is well controlled during the foot of the pulse, and that the entire implosion can be tuned symmetrically in the presence of the CBET in this system, with low levels of laser backscatter out of the hohlraum and low levels of hot electron production from intense laser–plasma interactions. Radiation hydrodynamic simulations can accurately represent the early shock symmetry and be used as a design tool, but cannot predict the late-time radiation flux symmetry during the peak of the pulse, and semi-empirical models are used to design the experiments. Deuterium–tritium (DT)-layered tests of 1100 μm inner radius implosions showed performance close to expectations from simulations at velocities up to ~360 km/s, and record yields at this velocity, when increasing the DT fuel layer thickness to mitigate hydrodynamic mixing of the ablator into the hot spot as a result of defects in the ablator. However, when the implosion velocity was increased, mixing due to these defects impacted performance. The ratio of measured to simulated yield for these experiments was directly correlated with the level of observed mixing. These simulations suggest that reducing the mixing, e.g., by improving the capsule defects, could result in higher performance. In addition, future experiments are planned to reduce the coast time at this scale, delay between the peak compression and the end of the laser, to increase the hot spot convergence and pressure. To reduce the coast time by several hundred ps compared to the 1100 μm inner radius implosions, HYBRID-E has also fielded 1050 μm inner radius capsules, which resulted in higher hot spot pressure and a fusion energy yield of ~170 kJ.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1987

Comparison of theoretical and experimental thrust performance of a 1030:1 area ratio rocket nozzle at a chamber pressure of 2413 kN/m2 (350 psia)

The joint Army. Navy, NASA. Air Force (JANNAF) rocket engine peformnace prediction procedure is based on the use of various reference computer programs. One of the reference programs for nozzle analysis is the Two-Dimensional Kinetics (TDK) Program. The purpose of this report is to calibrate the JANNAF procedure incorporated into the December l984 version of the TDK program for the high-area-ratio rocket engine regime. The calibration was accomplished by modeling the performance of a 1030:1 rocket nozzle tested at NASA Lewis Research Center. A detailed description of the experimental test conditions and TDK input parameters is given. The results show that the computer code predicts delivered vacuum specific impulse to within 0.12 to 1.9 percent of the experimental data. Vacuum thrust coefficient predictions were within + or - 1.3 percent of experimental results. Predictions of wall static pressure were within approximately + or - 5 percent of the measured values. An experimental value for inviscid thrust was obtained for the nozzle extension between area ratios of 427.5 and 1030 by using an integration of the measured wall static pressures. Subtracting the measured thrust gain produced by the nozzle between area ratios of 427.5 and 1030 from the inviscid thrust gain yielded experimental drag decrements of 10.85 and 27.00 N (2.44 and 6.07 lb) for mixture ratios of 3.04 and 4.29, respectively. These values correspond to 0.45 and 1.11 percent of the total vacuum thrust. At a mixture ratio of 4.29, the TDK predicted drag decrement was 16.59 N (3.73 lb), or 0.71 percent of the predicted total vacuum thrust.

Smith, Tamara A.↗
DOE OSTI2014

Black hole mass estimates and emission-line properties of a sample of redshift z > 6.5 quasars

We present the analysis of optical and near-infrared spectra of the only four z > 6.5 quasars known to date, discovered in the UKIDSS-LAS and VISTA-VIKING surveys. Our data set consists of new Very Large Telescope/X-Shooter and Magellan/FIRE observations. These are the best optical/NIR spectroscopic data that are likely to be obtained for the z > 6.5 sample using current 6-10 m facilities. We estimate the black hole (BH) mass, the Eddington ratio, and the Si IV/C IV, C III]/C IV, and Fe II/Mg II emission-line flux ratios. We perform spectral modeling using a procedure that allows us to derive a probability distribution for the continuum components and to obtain the quasar properties weighted upon the underlying distribution of continuum models. The z > 6.5 quasars show the same emission properties as their counterparts at lower redshifts. The z > 6.5 quasars host BHs with masses of ∼10{sup 9} M{sub ☉} that are accreting close to the Eddington luminosity ((log(L{sub Bol}/L{sub Edd})) = –0.4 ± 0.2), in agreement with what has been observed for a sample of 4.0 < z < 6.5 quasars. By comparing the Si IV/C IV and C III]/C IV flux ratios with the results obtained from luminosity-matched samples at z ∼ 6 and 2 ≤ z ≤ 4.5, we find no evidence of evolution of the line ratios with cosmic time. We compare the measured Fe II/Mg II flux ratios with those obtained for a sample of 4.0 < z < 6.4 sources. The two samples are analyzed using a consistent procedure. There is no evidence that the Fe II/Mg II flux ratio evolves between z = 7 and z = 4. Under the assumption that the Fe II/Mg II traces the Fe/Mg abundance ratio, this implies the presence of major episodes of chemical enrichment in the quasar hosts in the first ∼0.8 Gyr after the Big Bang.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2001

Simplified Analysis of Pulse Detonation Rocket Engine B1owdown Gasdynamics and Performance

Pulsed detonation rocket engines (PDREs) have generated considerable research interest in recent years as a chemical propulsion system potentially offering improved performance and reduced complexity compared to conventional rocket engines. The detonative mode of combustion employed by these devices offers a thermodynamic advantage over the constant-pressure deflagrative combustion mode used in conventional rocket engines and gas turbines. However, while this theoretical advantage has spurred a great deal of interest in building PDRE devices, the unsteady blowdown process intrinsic to the PDRE has made realistic estimates of the actual propulsive performance problematic. The recent review article by Kailasanath highlights some of the difficulties in comparing the available experimental measurements with numerical models. The goal of this paper is to improve understanding of PDRE blowdown gasdynamics and performance issues through use of a simplified model that captures the essential features of the unsteady blowdown process, and yet remains computationally inexpensive. The PDRE system studied here is highly idealized, consisting of a constant-area detonation tube with one end closed and the other end open to the environment. The tube is prefilled with a gaseous propellant mixture with no initial velocity or outflow to the environment. The detonation is initiated instantaneously at the closed end of the device. Chapman-Jouguet (C-J) post-detonation gas conditions are calculated using the CET89 version of the NASA thermochemical code. The I-D, unsteady method of characteristics is used to calculate the flowfield following the detonation front. See the compressible flow texts by Thompson and Zucrow and Hoffman for details of this method. Parametric studies of the effect of mixture stoichiometry, fill temperature, and blowdown pressure ratio on performance are reported. A comparison of the performance of an idealized straight-tube PDRE with a conventional steady-state rocket engine is provided. The effect of constant-gamma and equilibrium chemistry assumptions is also examined. Additionally, in order to form an assessment of the accuracy of the model, the flowfield time history is compared to experimental data from Stanford University.

Morris, Christopher I.↗
DOE OSTI2013

NEW EXTENDED DEUTERIUM FRACTIONATION MODEL: ASSESSMENT AT DENSE ISM CONDITIONS AND SENSITIVITY ANALYSIS

Observations of deuterated species are useful in probing the temperature, ionization level, evolutionary stage, chemistry, and thermal history of astrophysical environments. The analysis of data from the Atacama Large Millimeter Array and other new telescopes requires an elaborate model of deuterium fractionation. This paper presents a publicly available chemical network with multi-deuterated species and an extended, up-to-date set of gas-phase and surface reactions. To test this network, we simulate deuterium fractionation in diverse interstellar sources. Two cases of initial abundances are considered: (1) atomic except for H{sub 2} and HD, and (2) molecular from a prestellar core. We reproduce the observed D/H ratios of many deuterated molecules, and sort the species according to their sensitivity to temperature gradients and initial abundances. We find that many multiply deuterated species produced at 10 K retain enhanced D/H ratios at temperatures {approx}< 100 K. We study how recent updates to reaction rates affect calculated D/H ratios, and perform a detailed sensitivity analysis of the uncertainties of the gas-phase reaction rates in the network. We find that uncertainties are generally lower in dark cloud environments than in warm infrared dark clouds and that uncertainties increase with the size of the molecule and number of D-atoms. A set of the most problematic reactions is presented. We list potentially observable deuterated species predicted to be abundant in low- and high-mass star-formation regions.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Geothermal Life Cycle Calculator

This calculator is a handy tool for interested parties to estimate two key life cycle metrics, fossil energy consumption (Etot) and greenhouse gas emission (ghgtot) ratios, for geothermal electric power production. It is based solely on data developed by Argonne National Laboratory for DOE's Geothermal Technologies office. The calculator permits the user to explore the impact of a range of key geothermal power production parameters, including plant capacity, lifetime, capacity factor, geothermal technology, well numbers and depths, field exploration, and others on the two metrics just mentioned. Estimates of variations in the results are also available to the user.

15 GEOTHERMAL ENERGY↗
DOE OSTI2012

NON-NEUTRALIZED ELECTRIC CURRENT PATTERNS IN SOLAR ACTIVE REGIONS: ORIGIN OF THE SHEAR-GENERATING LORENTZ FORCE

Using solar vector magnetograms of the highest available spatial resolution and signal-to-noise ratio, we perform a detailed study of electric current patterns in two solar active regions (ARs): a flaring/eruptive and a flare-quiet one. We aim to determine whether ARs inject non-neutralized (net) electric currents in the solar atmosphere, responding to a debate initiated nearly two decades ago that remains inconclusive. We find that well-formed, intense magnetic polarity inversion lines (PILs) within ARs are the only photospheric magnetic structures that support significant net current. More intense PILs seem to imply stronger non-neutralized current patterns per polarity. This finding revises previous works that claim frequent injections of intense non-neutralized currents by most ARs appearing in the solar disk but also works that altogether rule out injection of non-neutralized currents. In agreement with previous studies, we also find that magnetically isolated ARs remain globally current-balanced. In addition, we confirm and quantify the preference of a given magnetic polarity to follow a given sense of electric currents, indicating a dominant sense of twist in ARs. This coherence effect is more pronounced in more compact ARs with stronger PILs and must be of sub-photospheric origin. Our results yield a natural explanation of the Lorentz force, invariably generating velocity and magnetic shear along strong PILs, thus setting a physical context for the observed pre-eruption evolution in solar ARs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Long-Term Photovoltaic System Performance in Cold, Snowy Climates

As countries around the world transition towards renewable energy, there is increasing interest in using photovoltaic (PV) technologies to help decarbonize northern and alpine communities due to their scalability and affordability. However, a barrier to large-scale adoption of PV in cold climates is long-term performance uncertainty under snowfall, freeze-thaw cycles, low temperatures, and high winds. In this work, we provide a comprehensive review of published silicon degradation rates in cold Koppen-Geiger climate classifications of Dfb (humid continental), Dfc (subarctic), and ET (tundra). We first analyze the system degradation rates of three subarctic ground-mounted photovoltaic sites in North America using the RdTools year-on-year method: an Al-BSF double-axis tracking site in Fairbanks, Alaska (65degrees N); a PERC and silicon heterojunction bifacial vertical and south-tilted site in Fairbanks, Alaska; and a PERC south-facing fixed-tilt site in Fort Simpson, Northwest Territories (62degrees N). Degradation rates of these newly analyzed sites vary between -0.4%/year and -1.5%/year. Combining these data with previously reported cold climate degradation rates, we show that the distribution of cold climate degradation peaks at -0.1%/year to -0.2%/year but has a large tail with rates above -0.5%/year. The average reported cold climate degradation rate is -0.45%/year, whereas the median value is -0.33%/year. These results suggest that despite frequent freeze-thaw cycles and potential exposure to high wind and snow loads, PV systems in cold climates tend to degrade slower than PV systems in warmer climates. The limited sample size of reported degradation rates in cold climates (27) motivates the need for further data acquisition and monitoring efforts as new technologies are deployed.

14 SOLAR ENERGY↗
DOE OSTI2013

Low energy probes of PeV scale sfermions

We derive bounds on squark and slepton masses in mini-split supersymmetry scenario using low energy experiments. In this setup gauginos are at the TeV scale, while sfermions are heavier by a loop factor. We cover the most sensitive low energy probes including electric dipole moments (EDMs), meson oscillations and charged lepton flavor violation (LFV) transitions. A leading log resummation of the large logs of gluino to sfermion mass ratio is performed. A sensitivity to PeV squark masses is obtained at present from kaon mixing measurements. A number of observables, including neutron EDMs, mu->e transitions and charmed meson mixing, will start probing sfermion masses in the 100 TeV-1000 TeV range with the projected improvements in the experimental sensitivities. We also discuss the implications of our results for a variety of models that address the flavor hierarchy of quarks and leptons. We find that EDM searches will be a robust probe of models in which fermion masses are generated radiatively, while LFV searches remain sensitive to simple-texture based flavor models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Operando visualization of porous metal additive manufacturing with foaming agents through high-speed x-ray imaging

Porous metals find extensive applications in soundproofing, filtration, catalysis, and energy-absorbing structures, thanks to their unique internal pore structure and high specific strength. In recent years, there has been an increasing interest in fabricating porous metals using additive manufacturing (AM), leveraging its unique advantages, including improved design freedom, spatial material control, and cost-effective small-batch production. In this study, we conducted pioneering operando visualization of AM porous metal using a laser powder bed fusion (L-PBF) setup combined with a high-speed synchrotron x-ray imaging system. Single track printing experiments using Ti6Al4V (Ti64) combined with titanium hydride (TiH 2 ) and sodium carbonate (Na 2 CO 3 ) as foaming agents, with varying mixing ratios were performed under different processing conditions. Here. the results elucidate the dynamic development of porosity formation. The average pore size is significantly influenced by the particle size of foaming agents when pore coalescence is absent. For all foaming agent content tested in the current study, the number of pores is found to be more sensitive to changes in laser power than in laser scanning speed. Increasing linear energy density (increasing laser power or reducing laser scanning speed) promotes the foaming agent activation thereby porosity formation. However, high linear energy density skews pore distribution towards the surface despite forming deeper melt pools. In addition, the impact of additional factors including foaming agent's laser absorptivity and decomposition kinetics with respect to AM time scales should be carefully considered to avoid ineffective activation of foaming agents during the AM of porous metals.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Understanding the Impacts of Biomass Blending on the Uncertainty of Hydrolyzed Sugar Yield from a Stochastic Perspective

Feedstock price and availability are key challenges for biorefinery development and biomass blending has been suggested as a route to overcome these limitations. However, the impacts of feedstock blending on the variability of yields of hydrolyzed sugar remained unclear. This study quantifies the uncertainties in the sugar yields from the blends of corn stover, switchgrass, and grass clippings by considering both variable and model uncertainties. The results indicate that feedstock blending reduces the uncertainties in sugar yields and delivers feedstock of more uniform quality. A further investigation on xxx demonstrates that the reduction in overall uncertainty is achieved by reduced compositional uncertainties of blended feedstock. Based on these results, the optimization of blending ratios was performed with respect to three objectives: (1) probability of meeting the sugar yield target; (2) expected sugar yields; and (3) sugar yield per unit feedstock expense, while satisfying constraints of feedstock availability and cost. In conclusion, the optimization method developed in this study, is readily applied to other combinations of feedstocks, biofuels production processes, and constraints.

09 BIOMASS FUELS↗