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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Numerical Analysis of Offshore Wind-Farm-Induced Drag Effects on Coastal Upwelling Dynamics

Wind farms extract momentum from the atmospheric flow, generating wind-speed deficits both within the plant, and extending downstream. When located offshore, these deficits modulate air-sea coupling, potentially impacting coastal upwelling in sensitive regions. We investigate impacts of wind farms on coastal upwelling using kilometre-scale, three-way-coupled simulations with the coupled ocean-atmosphere-wave-sediment transport system for the US West Coast. Wind-farm effects are represented by a generalised turbine drag formulation, an idealised, height-dependent body force whose magnitude is systematically varied. This approach isolates the leading-order fluid-dynamical response in a realistic coastal configuration. The atmospheric adjustment exhibits an approximately linear relation between drag force and wind-speed deficit, with wakes that expand downstream and increase in magnitude as drag increases. An empirical orthogonal function analysis of sea-surface-temperature anomalies reveals the emergence of a canonical dipole pattern under strong drag forcing. Subsurface diagnostics show consistent shoaling of the mixed layer and suppressed upward velocities in areas near wind-farm region, accompanied by compensating enhancements of shoaling closer to the coast. These results identify turbine drag as a control parameter in assessing interactions between wind-farm wake and coastal upwelling and provide scaling relationships for understanding offshore wind-farm effects on the coastal circulation dynamics.

16 TIDAL AND WAVE POWER↗
DOE OSTI2023

Giant Angular Nernst Effect in the Organic Metal α-(BEDT-TTF) 2 KHg(SCN) 4

We have detected a large Nernst effect in the charge density wave state of the multiband organic metal α-(BEDT-TTF) 2 KHg(SCN) 4 . We find that apart from the phonon drag effect, the energy relaxation processes that govern the electron–phonon interactions and the momentum relaxation processes that determine the mobility of the q1D charge carriers have a significant role in observing the large Nernst signal in the CDW state in this organic metal. The emphasised momentum relaxation dynamics in the low field CDW state (CDW 0 ) is a clear indicator of the presence of a significant carrier mobility that might be the main source for observation of the largest Nernst signal. The momentum relaxation is absent with increasing angle and magnetic field, i.e., in the high-field CDW state (CDW x ) as evident from the much smaller Nernst effect amplitude in this state. In this case, only the phonon drag effect and electron–phonon interactions are contributing to the transverse thermoelectric signal. Our findings advance and change previous observations on the complex properties of this organic metal.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High-frequency phonons drive large phonon-drag thermopower in semiconductors at high carrier density

It has been well established that (i) the thermopower of semiconductors can be enhanced through a phe- nomenon known as the drag effect, and (ii) the drag enhancement involves only low-frequency acoustic phonons and benefits from low electron densities and low temperatures. Using first-principles calculations we show that large drag enhancements to the thermopower are possible at high carrier density even at room temperature and arise from high-frequency acoustic phonons. A fascinating example is cubic boron arsenide (BAs) for which the calculated room temperature drag enhancement of the thermopower exceeds an order of magnitude at a high hole density of 10 21 cm –3 . This remarkable behavior stems from the simultaneously weak phonon-phonon and phonon-hole scattering of the high-frequency phonons in BAs that become drag active at high carrier densities through electron-phonon interactions. Furthermore, this work advances our understanding of coupled electron-phonon nanoscale transport and introduces an unexpected paradigm for achieving large thermopowers.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Gravitomagnetic vorticity generation in black hole accretion discs: a potential spatial constraint on plasma flow stability

We calculate the vorticity generation rate in the accretion disc near a slowly rotating black hole in the low-velocity, weak-field limit of general relativity. Specifically, we find that the frame-dragging effect due to the black hole’s rotation – manifested through the gravitomagnetic field – can generate vorticity in a moving plasma in the accretion disc. The mechanism remains operational as long as the accretion disc has non-negligible vertical height and is independent of the exact thermodynamical profile of the disc. The enstrophy density generation rate, as a measure of turbulence and dissipation, is presented, which indicates that the frame-dragging effect can disrupt the stability of the disc away from the z = 0 plane.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Photoinduced electric effects in various plasmonic materials

Photoinduced voltages associated with surface plasmon polariton excitations are studied both theoretically and experimentally in various plasmonic systems as the function of material, wavelength, and type of structure. Experimental photovoltage normalized to the absorbed power shows a general decrease upon an increase in the wavelength, enhancement in the nanostructured samples, and a strong variation in the magnitude as a function of the material, which are not in line with the theoretical predictions of the simple plasmonic pressure approach. Furthermore, the results can be used for clarification of the mechanisms and further development of an adequate theoretcial approach to the plasmon drag effect.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Tailoring grain growth and solid solution strengthening of single-phase CrCoNi medium-entropy alloys by solute selection

In the present study, we selected solutes to be added to the CrCoNi medium-entropy alloy (MEA) based on the mismatch of self-diffusion activation energy (SDQ) between the alloying elements and constituent elements of the matrix, and then investigated their grain growth behavior and mechanical properties. Mo and Al were selected as the solutes for investigation primarily because they have higher and lower SDQ, respectively, than those of the matrix elements; a secondary factor was their higher and lower shear modulus. Their concentrations were fixed at 3 at.% each because previous work had shown these compositions to be single-phase solid solutions with the face-centered cubic structure. Three alloys were produced by arc melting, casting, homogenizing, cold rolling and annealing at various temperatures and times to produce samples with different grain sizes. They were (a) the base alloy CrCoNi, (b) the base alloy plus 3 at.% Mo, and (c) the base alloy plus 3 at.% Al. The activation energies for grain growth of the CrCoNi, CrCoNi-3Mo and CrCoNi-3Al MEAs were found to be ~251, ~368 and ~219 kJ/mol, respectively, consistent with the notion that elements with higher SDQ (in this study Mo) retard grain growth (likely by a solute-drag effect), whereas those with lower values (Al) accelerate grain growth. The room-temperature tensile properties show that Mo increases the yield strength by ~40% but Al addition has a smaller strengthening effect consistent with their relative shear moduli. The yield strength as a function of grain size for the three singlephase MEAs follows the classical Hall-Petch relationship with much higher slopes (> 600 MPa μm -0.5 ) than traditional solid solutions. Furthermore, this work shows that the grain growth kinetics and solid solution strengthening of the CrCoNi MEA can be tuned by selecting solute elements that have appropriate diffusion and physical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Turbulent kinetic energy over large offshore wind farms observed and simulated by the mesoscale model WRF (3.8.1)

Abstract. Wind farms affect local weather and microclimates;hence, parameterizations of their effects have been developed for numerical weather prediction models.While most wind farm parameterizations (WFPs) include drag effects of wind farms, models differ on whether or not an additionalturbulent kinetic energy (TKE) source should be included in theseparameterizations to simulate the impact of wind farms on the boundary layer.Therefore, we use aircraft measurements above large offshore wind farms in stable conditions to evaluateWFP choices. Of the three case studies we examine, we find the simulated ambient backgroundflow to agree with observations of temperature stratification and winds. This agreement allows us toexplore the sensitivity of simulated wind farm effects with respect to modeling choicessuch as whether or not to include a TKE source, horizontal resolution, vertical resolutionand advection of TKE. For a stably stratified marine atmospheric boundary layer (MABL), a TKE source and a horizontal resolutionon the order of 5 km or finer are necessary to represent the impact of offshore wind farms on the MABL.Additionally, TKE advection results in excessively reduced TKE over the wind farms, which in turn causesan underestimation of the wind speed deficit above the wind farm. Furthermore, using fine verticalresolution increases the agreement of the simulated wind speed with satellite observations of surface wind speed.

17 WIND ENERGY↗
DOE OSTI2022

Emergence of asymmetric skew-scattering dominated anomalous Nernst effect in the spin gapless semiconductors Co 1+x Fe 1-x CrGa

Heusler alloy-based spin gapless semiconductors (SGSs) with very high Curie temperatures ( T C ) have recently gained enormous attention because of their unconventional electronic structures. They exhibit a nonzero band gap in one of the spin channels and a zero band gap in the other spin channel, making them an important class of materials for tunable spin transport. Here, we report the experimental observation of anomalous Nernst effect (ANE) in Co 1 + x Fe 1 - x CrGa ( x = 0 , 0.2, 0.4, and 0.5), which are the emerging quaternary Heusler alloy-based SGSs. While the electron-electron elastic scattering and the disorder-mediated weak localization effect play the major roles in electrical transport for all the samples at low temperatures, the magnon-drag effect was found to dominate the longitudinal thermoelectric transport. The ANE coefficient at room temperature increases from ≈ 0.018 μ V K - 1 for x = 0 to ≈ 0.063 μ V K - 1 for x = 0.5 , which is higher than that for Ni 81 Fe 19 and compressively strained SrRu O 3 films. Our analysis indicates that the observed ANE in these samples originates from asymmetric skew scattering of charge carriers.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Impact of boundary layer simulation on predicting radioactive pollutant dispersion: a case study for HANARO Research Reactor using the WRF-MMIF-CALPUFF modeling system

Wind plays an important role in cases of unexpected radioactive pollutant dispersion, deciding distribution and concentration of the leaked substance. The accurate prediction of wind has been challenging in numerical weather prediction models, especially near the surface because of the complex interaction between turbulent flow and topographic effect. As such, in this study, we investigated the characteristics of atmospheric dispersion of radioactive material (i.e. 137 Cs) according to the simulated boundary layer around the HANARO research nuclear reactor in Korea using the Weather Research and Forecasting (WRF)-Mesoscale Model Interface (MMIF)-California Puff (CALPUFF) model system. We examined the impacts of orographic drag on wind field, stability calculation methods, and planetary boundary layer parameterizations on the dispersion of radioactive material under a radioactive leaking scenario. We found that inclusion of the orographic drag effect in the WRF model improved the wind prediction most significantly over the complex terrain area, leading the model system to estimate the radioactive concentration near the reactor more conservatively. We also emphasized the importance of the stability calculation method and employing the skillful boundary layer parameterization to ensure more accurate low atmospheric conditions, in order to simulate more feasible spatial distribution of the radioactive dispersion in leaking scenarios.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Stabilization of high-performance rock-salt LiMnSbTe3 thermoelectrics with embedded van der Waals-like gaps

Rock-salt-structured compounds like lead chalcogenides are promising thermoelectrics, as their high symmetry, strong anharmonicity, and favorable phase behavior collectively lead to high performance by enabling large power factors and ultralow thermal conductivity. Here, we report LiMnSbTe 3 , a new rock-salt semiconductor stabilized through targeted chemical design by combining hexagonal MnTe with cubic LiSbTe 2 . Embedded in the highsymmetry matrix, van der Waals-like gaps form due to Sb 2 Te 3 nanoscale segregation, which acts as effective phonon-scattering centers, leading to a low lattice thermal conductivity of 0.37Wm- 1 K -1 at 873 K with alloy scattering from disordered cations. The ordered local structure of Sb2Te 3 -type vdW-like gaps and the cross-gap interaction facilitate the carrier transport. Aided by energyconverged valence bands and a paramagnon drag effect, high Seebeck coefficients and enhanced power factor can be achieved, leading to a high ZT of 1.2 at 873 K. Furthermore, introducing Mn deficiency increases ZT to 1.5, highlighting the potential for higher performance through optimized doping or alloying. A segmented single-leg thermoelectric module achieves an output power density of 0.52 Wcm -2 and an efficiency of 8.7% under ΔT of 478 K, further demonstrating its promising thermoelectric applications.

42 ENGINEERING↗
DOE OSTI2025

Driven probe particle dynamics in a bubble and pattern forming system

We numerically examine the dynamics of a probe particle driven at a constant force through an assembly of particles with competing long-range repulsion and short-range attraction that forms a bubble or stripe state. In the bubble regime, we identify several distinct types of motion, including an elastic or pinned regime where the probe particle remains inside a bubble and drags all other bubbles with it. There is also a plastic bubble phase where the bubble in which the probe particle is trapped is able to move past the adjacent bubbles. At larger drives, there is a breakthrough regime where the probe particle jumps from bubble to bubble and, in some cases, can induce correlated rotations or plastic rearrangements of the particles within the bubbles. At the highest drives, the probe particle moves sufficiently rapidly that the background particles undergo only small distortions. The distinctive dynamic flow states and the transitions between them are accompanied by signatures in the effective drag on the driven particle, jumps in the velocity–force curves, and changes in the time-dependent velocity fluctuations. We map the dynamic phase diagram for this system for varied interaction lengths, bubble sizes, and densities.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The effect of terrain-influenced winds on fire spread in QUIC-Fire

Here in this manuscript, we describe the implementation of the terrain-following version of QUIC-URB into QUIC-Fire and a demonstration of the impacts of terrain-influenced winds on QUIC-Fire-simulated fire spread. No changes to the underlying QUIC-Fire fire spread algorithm were made other than what was required to correctly account for the inclusion of terrain. This paper summarizes simulations used to understand how the QUIC-URB terrain-influenced winds affect upslope fire behavior without additional changes to the QUIC-Fire fire spread algorithm. Previously published FIRETEC results are compared to simulation results from the modified QUIC-Fire (incorporating terrain-influenced winds) that use the same topographies and fuels. QUIC-Fire results showed overall similar behaviors in terms of how the topographies affected fire shapes and trends in spread rates. Due to the terrain-following version of QUIC-URB being unable to generate flow separations at the crest of hills, fire spread rates in these regions across all non-flat topographies were over-predicted when compared to FIRETEC. Lateral fire growth showed similar trends with FIRETEC between topographies but did not capture the increase in spread due to a diagonal interface between grassland and forested fuel regions in the test domain. These simulations suggest possible refinements that are necessary to improve QUIC-Fire and thus guide ongoing efforts related to: how flame tilt angle is accounted for, the incorporation of non-local drag effects, and the inclusion of the wake-eddy parameterizations that are used in QUIC-URB.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Terrain-Influenced Winds and Fire-Fire Interactions in Wildland Fire Simulations [Dissertation]

Ensemble-based approaches to prescribed fire planning cannot be supported by computational fluid dynamics based models like FIRETEC and the Wildland-Urban Interface Fire Dynamics Simulator (WFDS) because they are too computationally expensive and cannot leverage large eddy simulation approaches like CAWFE and WRF-SFIRE because they have too coarse of resolution. QUIC-Fire was developed to fill this gap but it cannot currently address complex terrain, that is typical for instance in the Western United States. This dissertation describes a variety of improvements made to QUIC-Fire and its various incorporated algorithms in an effort to make it a viable tool in simulating wildland and prescribed fires on terrain. The modifications made to QUIC-Fire are described in three chapters. The first chapter describes the extension of the diagnostic wind model QUIC-URB, the wind engine of QUIC-Fire, to a terrain-following coordinate system. The terraininfluenced winds it generates are analyzed and compared. In particular, this chapter presents the mathematical derivation of the wind solver leading to a linear system of equations that are solved through the successive over-relaxation method. The model is validated against a standard test used in previous works (the Askervein Hill) and against a new dataset from measurements in the Socorro Mountains, New Mexico. The terrain-following implementation captures the correct phenomenology for the isolated Askervein Hill, with a wind speed up at the top of the hill. The model agrees well with measurements on the upwind side of the peak, but overestimates speed-up on the downwind side of the hill. This is due to the inability of the model to generate flow separation and wake-eddy dynamics. On a common laptop, the divergence-free wind field is obtained in 6 s, making the solver appealing for coupled fire-atmosphere simulations. The Socorro Mountain is highly complex, with many cliff faces, peaks, and valleys. Although the model captures the magnitude and direction of inlet and outlet areas of the domain, it performs rather poorly in the valley region and in the regions near the steep cliffs. Hence, the model shows good agreement with data in areas of open sloped terrain but lacks in areas where flow separation and thermally driven effects may be present (neither effect is addressed in this work). In the second chapter the implementation of the terrain-following version of QUIC-URB into QUIC-Fire, and the necessary changes needed to include terrain are described. No changes to the underlying fire spread algorithm are made other than what is required to correctly account for the inclusion of terrain. Previously published FIRETEC results that use five different topographies that share the same centerline profile are compared to simulation results from the modified QUIC-Fire that use the same topographies and fuels. QUIC-Fire results show overall similar behaviors in terms of how the topographies affect fire shapes and trends in spread rates. Due to the terrain-following version of QUIC-URB being unable to generate flow separations at the crest of hills, fire spread rates in these regions across all topographies are over-predicted when compared to FIRETEC. Lateral fire growth shows similar trends with FIRETEC between topographies but does not capture the increase in spread due to a diagonal interface between grassland and forested fuel region of the domain. These results suggest that there are three algorithms within QUIC-Fire that could use improvement: how flame tilt angle is accounted for, the incorporation of non-local drag effects, and the inclusion of the wake-eddy parameterizations that are used in QUIC-URB. Lastly, the third chapter describes a modification to the initial guess used for the calculation of the QUIC-URB mass-conserved wind solution during fire simulations. The modification is aimed at improving fire-fire interactions in QUIC-Fire simulations. The modification consists of using the solution from the previous timestep as the starting point for the calculation of the solution for the next timestep. Fire-fire interactions is greatly improved by the change but a new source of error is introduced. Due to how plumes are modelled in QUIC-Fire the new solution contains errors where gaps in the plume structure are present. However, these errors are mostly limited to the upper atmosphere, where they do not affect fire behavior at the surface, and their magnitude isn’t significant enough to discount the amount of new fire phenomenology now captured in QUIC-Fire with the change.

58 GEOSCIENCES↗
DOE OSTI2021

Global and local texture development during initial plastic deformation of cold-pilgered Zircaloy-4 tubing

In this work we present a thorough characterization of the texture development during the initial step of a cold pilgering process of a Zircaloy-4 TREX tube, on which the axial cross section is reduced by 80% over a 40cm length with an overall Q-ratio of 2.34, followed by a recrystallization thermal treatment. Texture across a tapered specimen representing this working zone was characterized by neutron diffraction and high energy synchrotron x-ray diffraction at 28 positions (4 locations along its length and 7 locations across its thickness with 0.3 mm spatial resolution), and on the deformed end after the thermal treatment. Results show that the starting material (TREX tube) presents a texture gradient through its wall thickness, with the c poles aligned to the hoop direction at the outer surface (with radial and hoop Kearns factors: f R =0.36, f H = 0.50), and gradually rotating around the axial direction to become a quasi-radial orientation (~35 o out of the radial direction) at the inner surface ( f R =0.43, f H =0.35). The overall texture becomes more radial due to the cold pilgering, but the texture gradient remains during the whole deformation process, being always more radial at the inner surface, ( f R =0.53, f H =0.37 at 80%) than at the outer surface ( f R =0.41, f H =0.50at 80%). The most remarkable changes in texture produced by the rolling process is a 30 o rotation of the grains around their c-axis, producing a marked increase of the <11 2 ¯ 0> // axial fiber texture at expenses of the original <10 1 ¯ 0> // axial fiber texture observed in the TREX tube. The observed changes in texture during deformation were correctly explained by visco-plastic self-consistent (VPSC) modelling. This was achieved after the inclusion of the basal <a> slip system, which plays a central role to explain the 30 o rotation around the c-axis during deformation. The texture evolution was correctly described after the inclusion of a drag effect to grain rotation due to the interaction with neighbouring grains. The through thickness texture differences are greatly reduced by the recrystallization thermal treatment, with similar Kearns factors at the inner surface ( f R =0.50, f H =0.28) and the outer surface ( f R =0.48, f H =0.39). The predominance of the <10 1 ¯ 0> // axial fiber texture is recovered after recrystallization.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Colossal Nernst power factor in topological semimetal NbSb 2

Today solid-state cooling technologies below liquid nitrogen boiling temperature (77 K), crucial to quantum information technology and probing quantum state of matter, are greatly limited due to the lack of good thermoelectric and/or thermomagnetic materials. Here, we report the discovery of colossal Nernst power factor of 3800 × 10 -4 W m -1 K -2 under 5 T at 25 K and high Nernst figure-of-merit of 71 × 10 -4 K -1 under 5 T at 20 K in topological semimetal NbSb 2 single crystals. The observed high thermomagnetic performance is attributed to large Nernst thermopower and longitudinal electrical conductivity, and relatively low transverse thermal conductivity. The large and unsaturated Nernst thermopower is the result of the combination of highly desirable electronic structures of NbSb 2 having compensated high mobility electrons and holes near Fermi level and strong phonon-drag effect. This discovery opens an avenue for exploring material option for the solid-state heat pumping below liquid nitrogen temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Dynamic substrate reactions during room temperature heavy ion irradiation of CoCrCuFeNi high entropy alloy thin films

Abstract High entropy alloys (HEAs) are promising materials for various applications including nuclear reactor environments. Thus, understanding their behavior under irradiation and exposure to different environments is important. Here, two sets of near-equiatomic CoCrCuFeNi thin films grown on either SiO 2 /Si or Si substrates were irradiated at room temperature with 11.5 MeV Au ions, providing similar behavior to exposure to inert versus corrosion environments. The film grown on SiO 2 had relatively minimal change up to peak damage levels above 500 dpa, while the film grown on Si began intermixing at the substrate–film interface at peak doses of 0.1 dpa before transforming into a multi-silicide film at higher doses, all at room temperature with minimal thermal diffusion. The primary mechanism is radiation-enhanced diffusion via the inverse Kirkendall and solute drag effects. The results highlight how composition and environmental exposure affect the stability of HEAs under radiation and give insights into controlling these behaviors.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Magnetically dependent photovoltages in permalloy films and gratings

Significant photoinduced voltages observed in permalloy structures consist of two contributions with different origins, which depend on illumination conditions, structure geometry and magnetic field in distinct ways. The first component is the plasmon drag effect voltage closely associated with plasmon propagation. The second contribution is magnetically dependent and can be related to photoinduced gradients in the sample temperature and spin polarization. Possible mechanisms of the effect are discussed

36 MATERIALS SCIENCE↗