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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
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↗
NASA NTRS1985

A numerical study of global axisymmetric states and their stability to quasi-geostrophic disturbances

A steady, axisymmetric model of the general circulation is developed as a basis for climate stability studies. The model includes the effects of heating, rotation, and internal friction, but neglects topography. It is assumed that the axisymmetric flow may be modeled by making the Boussinesq and deep convection approximations. The hydrostatic assumption is not made, thus permitting the advective terms to be included in the vertical equation of motion. The initial set of five primitive equations is reduced to three equations in terms of the zonal velocity, meridional streamfunction, and the potential temperature perturbation. The application of the Boussinesq, deep convection, and quasi-geostrophic assumptions limits the ranges of the heating and rotation rates. For values not too far from typical atmospheric values, the model produces a stability boundary separating Hadley from Rossby flow. The boundary is characterized by a particular value of vertical wind shear, which suggests that baroclinic instability is the primary mechanism for the loss of stability. The initial growth rates are largest for longitudinal waves 4-7, also in agreement with studies of baroclinic instability.

Henderson, H. W.↗
NASA NTRS1987

The wind-disk interaction in X-ray burst sources. II - Collimation by thick accretion disks

The wind-disk interaction model in type I cosmic X-ray bursts is here examined in the case where the accretion disk surrounding the neutron star is geometrically thick. The funnel structure along the rotation axis of such a system may collimate the radiatively driven wind following a thermonuclear flash in the star's surface layers, and could thereby enhance the radiative flux (diffusive plus advective) along the beam direction. It is shown that for plausible conditions, this mechanism can account for the super-Eddington fluxes observed in some bursts. The overall time scale for variability, the color temperature, and the spectral shape in this picture are consistent with the observed properties of type I X-ray bursts.

Melia, Fulvio↗
NASA NTRS2020

Fast Responses on Pre-Industrial Climate from Present-Day Aerosols in A CMIP6 Multi-Model Study

In this work, we use Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations from 10 Earth system models (ESMs) and general circulation models (GCMs) to study the fast climate responses on pre-industrial climate, due to present-day aerosols. All models carried out two sets of simulations: a control experiment with all forcings set to the year 1850 and a perturbation experiment with all forcings identical to the control, except for aerosols with precursor emissions set to the year 2014. In response to the pattern of all aerosols effective radiative forcing (ERF), the fast temperature responses are characterized by cooling over the continental areas, especially in the Northern Hemisphere, with the largest cooling over East Asia and India, sulfate being the dominant aerosol surface temperature driver for present-day emissions. In the Arctic there is a warming signal for winter in the ensemble mean of fast temperature responses, but the model-to-model variability is large, and it is presumably linked to aerosol-induced circulation changes. The largest fast precipitation responses are seen in the tropical belt regions, generally characterized by a reduction over continental regions and presumably a southward shift of the tropical rain belt. This is a characteristic and robust feature among most models in this study, associated with weakening of the monsoon systems around the globe (Asia, Africa and America) in response to hemispherically asymmetric cooling from a Northern Hemisphere aerosol perturbation, forcing possibly the Intertropical Convergence Zone (ITCZ) and tropical precipitation to shift away from the cooled hemisphere despite that aerosols' effects on temperature and precipitation are only partly realized in these simulations as the sea surface temperatures are kept fixed. An interesting feature in aerosol-induced circulation changes is a characteristic dipole pattern with intensification of the Icelandic Low and an anticyclonic anomaly over southeastern Europe, inducing warm air advection towards the northern polar latitudes in winter.

Pre-industrial climate↗
NASA NTRS1977

Computational design of the basic dynamical processes of the UCLA general circulation model

The 12-layer UCLA general circulation model encompassing troposphere and stratosphere (and superjacent 'sponge layer') is described. Prognostic variables are: surface pressure, horizontal velocity, temperature, water vapor and ozone in each layer, planetary boundary layer (PBL) depth, temperature, moisture and momentum discontinuities at PBL top, ground temperature and water storage, and mass of snow on ground. Selection of space finite-difference schemes for homogeneous incompressible flow, with/without a free surface, nonlinear two-dimensional nondivergent flow, enstrophy conserving schemes, momentum advection schemes, vertical and horizontal difference schemes, and time differencing schemes are discussed.

Arakawa, A.↗
NASA NTRS1982

Mature thunderstorm cloud top structure - Three-dimensional numerical simulation versus satellite observations

Preliminary results of four runs with a three-dimensional model of the effects of vertical wind shear on cloud top height/temperature structure and the internal properties of isolate midlatitude thunderstorms are reported. The model is being developed as an aid to analyses of GEO remote sensing satellite data. The grid is a 27 x 27 x 20 mesh with 2 km horizontal resolution and 0.9 vertical resolution. The total grid is 54 km on a side and 18 km deep. A second-order Crowley scheme for advecting momentum is extended with a third-order correction for spatial truncation error, and the earth-relative horizontal surface wind components are decreased to 50 percent of their values at 0.45 km. A temperature increase with height is included, together with an initial impulse consisting of a nonrotating cylindrical weak buoyant updraft 10 km in radius. The results of the runs are discussed in terms of the time variation of the vertical velocity extrema, the effects of strong and weak shear on a storm, the cloud top height, the Lagrangian dynamics of a thermal couplet, and data from a real storm.

Schlesinger, R. E.↗
NASA NTRS1996

The 5-6 December 1991 FIRE IFO 2 Jet Stream Cirrus Case Study: Possible Influences of Volcanic Aerosols

In presenting an overview of the cirrus clouds comprehensively studied by ground based and airborne sensors from Coffeyville, Kansas, during the 5-6 December 1992 First ISCCP Regional Experiment (FIRE) intensive field observation (IFO) case study period, evidence is provided that volcanic aerosols from the June 1991 Pinatubo eruptions may have significantly influenced the formation and maintenance of the cirrus. Following the local appearance of a spur of stratospheric volcanic debris from the subtropics, a series of jet streaks subsequently conditioned the troposphere through tropopause foldings with sulfur based particles that became effective cloud forming nuclei in cirrus clouds. Aerosol and ozone measurements suggest a complicated history of stratospheric-tropospheric exchanges embedded with the upper level flow, and cirrus cloud formation was noted to occur locally at the boundaries of stratospheric aerosol enriched layers that became humidified through diffusion, precipitation, or advective processes. Apparent cirrus cloud alterations include abnormally high ice crystal concentrations (up to approximately 600 L(exp. 1)), complex radial ice crystal types, and relatively large haze particles in cirrus uncinus cell heads at temperatures between -40 and -50 degrees C. Implications for volcanic-cirrus cloud climate effects and unusual (nonvolcanic) aerosol jet stream cirrus cloud formation are discussed.

Sassen, Kenneth↗
DOE OSTI2024

Recent Advanced Reactor Multiphysics Model Highlights in the Virtual Test Bed (VTB)

The Virtual Test Bed (VTB) host over 30 distinct simulations that showcase state-of-the art capabilities across the national lab complex. An update on the status of models on the VTB is summarized here, along with a more detailed overview of select recent new capabilities to showcase. All of the major advanced reactor types are represented in the VTB. The first example consists of a multiphysics simulation to track the transport of species in Molten Salt Reactors using depletion, advection, and thermochemical calculations. The second consists of a coupled neutronic and thermal hydraulic simulation to validate a gas cooled reactor. The third consist of pebble-bed equilibrium model for a fluoride high-temperature reactor. The fourth is a high-fidelity neutronic and thermal hydraulic model of a liquid metal reactor assembly. And lastly the fifth consists of transient multiphysics simulations of heat pipe microreactors.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS2006

Modeling the Observed QBO and Inter-Annual Variations of the Diurnal Tide in the Mesosphere

In the current version of the Numerical Spectral Model (NSM), the Quasi-biennial Oscillation (QBO) is generated primarily by small-scale gravity waves (GW) from Hines' Doppler Spread Parameterization (DSP). The model does not have topography, and the planetary waves are solely generated by instabilities. We discuss a 3D modeling study that describes the QBO extending from the stratosphere into the upper mesosphere, where the oscillation produces significant inter-annual variations in the diurnal tide. The numerical results are compared with temperature measurements from the SABER (TIMED) and MLS (UARS) instruments obtained by Huang et al. (2006). With a GW source that peaks at the Equator and is taken to be isotropic and independent of season, the NSM generates a QBO with variable periods around 26 months and zonal wind amplitudes of almost 25 m/s at 30 km. As reported earlier, the NSM reproduces the observed equinoctial maxima in the diurnal tide at altitudes around 95 km. The modeled QBO modulates the tide such that the seasonal amplitude maxima can vary from one year to another by as much as 30%. To shed light on the underlying mechanisms, the relative importance of the advection terms are discussed, and they are shown to be important in the stratosphere. At altitudes above 80 km, however, the QBO-related inter-annual variations of the tide are generated primarily by GW momentum deposition. In qualitative agreement with the SABER measurements, the model generates distinct zonal-mean QBO temperature variations in the stratosphere and mesosphere. In the stratosphere, the computed amplitudes are not much smaller than those observed, and the rate of downward propagation at the Equator is reproduced. The modeled temperature amplitudes in the mesosphere, however, are much smaller than those observed. The observed and computed temperature variations of the QBO peak at the Equator but extend with phase reversals to high latitudes, in contrast to the zonal winds that are confined to equatorial latitudes. Hemispherical asymmetries also appear in both the model results and the observations. The temperature amplitudes outside the equatorial region however tend to occur at lower latitudes in the model results. While there is qualitative agreement between the TIMED measurements and the model prediction, there are some areas of significant disagreement that require us to reexamine the present version of the NSM. The numerical results critically depend on the chosen parameters that determine the wave forcing, and there are a number of avenues to improve the performance of the model that had not been tuned to fit the observations. The GW spectrum and its latitude dependence in the troposphere are not well known, and numerical experiments are discussed that describe the related model response. While it appears that eastward propagating Kelvin waves and westward propagating Rossby gravity waves are not the primary source to generate the QBO, the GW forcing can seed the oscillation and act as a catalyst to enhance effectiveness of these planetary waves.

Mayr, Hans G.↗
DOE OSTI2021

NRC Multiphysics Analysis Capability Deployment FY21: Part 3

This report details the progress and activities of Idaho National Laboratory (INL) on the Nuclear Regulatory Commission (NRC) project “Development and Modeling Support for Advanced Non-Light Water Reactors.” The deliverables completed for this report are: Deliverable 1c: the capability to model gas mixtures was added to Pronghorn. A test problem mimicking the conditions achieved in a depressurized loss of forced cooling (DLOFC) event was solved with both RELAP-5 and Pronghorn. Pronghorn employed a finite vol ume method with the Kurganov-Tadmor discretization. The comparison between the mass fraction spatial profiles computed with RELAP-5 and Pronghorn clearly shows the presence of numerical artifacts (i.e., overly diffusive behavior at low Mach numbers). We confirmed that the problem disappears at higher Mach numbers. We recommend future work on the implementation of a low Mach finite volume formulation to better treat low Mach number problems. Deliverable 2a: we demonstrated two approaches to model the radiation/conduction/natural convection heat transfer across a stagnant gas for the PBMR-400 design using Pronghorn. The first approach is based on the net radiation method, which relies on the computation of view factors with the Multiphysics Object-Oriented Simulation Environment (MOOSE) ray tracing capability. The second method is a traditional thermal resistance approach. The test problems include both 2D and 3D geometries. In all cases, the results show very good agreement during a DLOFC transient. This confirms that the faster thermal resistance method produces solutions that are equivalent to the net radiation method for this geometry. Deliverable 3d: we demonstrated the use of the advection kernel for the delayed neutron precursor equation in Griffin with a 2D MSFR model. The results appear physical but further verification is recommended. We also recommend the addition of conjugate heat transfer to compute the temperatures and model the thermomechanic behavior of the reflectors and other structures. Significant memory and performance issues were encountered in the 3D axisymmetric model. Future work is recommended in this area. Task 8g: this task allows multidimensional MOOSE applications to be coupled to system codes (RELAP-7 and SAM). We implemented a faster multiphysics iteration coupling algorithm, which provides an overall 6× acceleration of the 3D-1D coupling of the core multidi- mensional fluid flow solver and the 1D primary and secondary loop model.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1986

Meridional distribution of stratospheric trace constituents

Vertically stratified tracers such as methane and nitrous oxide tend to have constant mixing ratio surfaces that slope downward toward the poles in the meridional plane. The equilibrium tracer slope results from the competition between the slope steepening effects of advection by the diabatic circulation and the slope flattening effects of quasi-isentropic eddy transport and photochemical loss. The diabatic circulation iself is, however, driven primarily by eddy transports, which maintain the departure of stratospheric temperatures from radiative equilibrium. If the eddy transports are weak, the diabatic circulation is also weak and the slope is small. Using a simple beta-plane channel model and an eddy diffusion parameterization for the eddy potential vorticity and tracer transports, it is shown that the slope is a maximum for a value of eddy diffusion such that the dynamical time scale lies between the radiative and chemical time scales.

Holton, J. R.↗
NASA NTRS1986

Mathematical model for the Bridgman-Stockbarger crystal growing system

In a major technical breakthrough, a computer model for Bridgman-Stockbarger crystal growth was developed. The model includes melt convection, solute effects, thermal conduction in the ampule, melt, and crystal, and the determination of the curved moving crystal-melt interface. The key to the numerical method is the use of a nonuniform computational mesh which moves with the interface, so that the interface is a mesh surface. In addition, implicit methods are used for advection and diffusion of heat, concentration, and vorticity, for interface movement, and for internal gracity waves. This allows large time-steps without loss of stability or accuracy. Numerical results are presented for the interface shape, temperature distribution, and concentration distribution, in steady-state crystl growth. Solutions are presented for two test cases using water, with two different salts in solution. The two diffusivities differ by a factor of ten, and the concentrations differ by a factor of twenty.

Roberts, G. O.↗
NASA NTRS1994

Effect of lightning on the concentration of odd nitrogen species in the lower stratosphere: An update

Revised model estimates of the effect of lightning on the lower stratospheric NOy are presented. Several changes in the Atmospheric and Environmental Research Incorporated model were made since the last evaluation of the impact of lightning. Improvements were made in the model circulation and location of tropopause in the tropics, which is now calculated from the National Meteorological Center temperature data. Changes in model circulation reduced the mass flux from the troposphere to the tropical stratosphere. The calculated mass fluxes are found to agree better with some recent estimates. The circulation changes also reduced the advective mass flux from the tropical lower stratosphere to the midlatitudes. The change in circulation and the change in the tropopause height lead to increases in the calculated concentration of N2O, O3 and NOy in the tropical lower stratosphere. The effect of lightning is to increase the calculated concentration of NOy around 64 mbar by a factor of 2, compared to a factor of 10 enhancement in the previous calculations. Comparison with the Stratosphere Troposphere Exchange Project 1987 data indicates that the inclusion of a lightning source brings the model results in closer agreement with the observations.

Kotamarthi, V. R.↗
DOE OSTI2024

Dissolution zone model of the oxide structure in additively manufactured dispersion-strengthened alloys

The structural evolution of oxides in dispersion-strengthened superalloys during laser-powder bed fusion is considered in detail. Alloy chemistry and process parameter effects on oxide structure are assessed through a parameter study on the model alloy Ni-20Cr, doped with varying concentrations of Y 2 O 3 and Al. Small angle neutron scattering measurements of the dispersoid size distribution show the dispersoid size increases with higher laser power, slower scan speed, and increasing Y 2 O 3 and Al content. Complementary electron microscopy measurements reveal reactions between Y 2 O 3 and Al, even in nanoscale dispersoids, and the presence of micron-scale oxide slag inclusions in select specimens. A scaling analysis of mass and momentum transport within the melt pool, presented here, establishes that diffusional structural evolution mechanisms dominate for nanoscale dispersoids, while fluid forces and advection become significant for larger slag inclusions. These findings are developed into a theory of dispersoid structural evolution, integrating quantitative models of diffusional processes – dispersoid dissolution, nucleation, growth, coarsening – with a reduced order model of time-temperature trajectories of fluid parcels within the melt pool. Calculations of the dispersoid size in single-pass melting reveal a zone in the center of the melt track in which the oxide feedstock fully dissolves. Within this zone the final Y 2 O 3 size is independent of feedstock size and determined by nucleation and growth kinetics. If the dissolution zones of adjacent melt tracks overlap sufficiently with each other to dissolve large oxides, formed during printing or present in the powder feedstock, then the dispersoid structure throughout the build volume is homogeneous and matches that from a single pass within the dissolution zone. Gaps between adjacent dissolution zones result in oxide accumulation into larger slag inclusions. Predictions of final dispersoid size and slag formation using this dissolution zone model match the present experimental data and explain process-structure linkages speculated in the open literature.

36 MATERIALS SCIENCE↗
NASA NTRS1993

The 5-6 December 1991 FIRE IFO 2 jet stream cirrus case study: The influence of volcanic aerosols

In presenting an overview of the cirrus clouds comprehensively studied by ground-based and airborne sensors from Coffeyville, KS, during the 5-6 Dec. 1992 Project FIRE (First International Satellite Cloud Climatology Project Regional Experiment) IFO II case study period, evidence is provided that volcanic aerosols from the June 1991 Pinatubo eruptions significantly influenced the formation and maintenance of the cirrus. Following the local appearance of a spur of stratospheric volcanic debris from the subtropics, a series of jet streaks subsequently conditioned the troposphere through tropopause foldings with sulfur-based particles that became effective cirrus cloud-forming nuclei. Aerosol and ozone measurements suggest a complicated history of stratospheric-tropospheric exchanges embedded within the upper level flow, and cirrus cloud formation was noted to occur locally at the boundaries of stratospheric aerosol-enriched layers that became humidified through diffusion, precipitation, or advective processes. Apparent cirrus cloud alterations include abnormally high ice crystal concentrations (up to approximately 600 l(sup -1), small but complex radial ice crystal types, and relatively large haze particles in cirrus uncinus cell heads at temperatures between -40 to -50 C. Implications for volcanic-cirrus cloud climate effects, and usual (non-volcanic aerosol) jet stream cirrus cloud formation are discussed.

Sassen, Kenneth↗
NASA NTRS1995

GOES weather satellite observations and measurements of the May 18, 1980, Mount St. Helens eruption

We demonstrate the use of Geostationary Operational Environmental Satellite (GOES) images of the May 18, 1980, Mount St. Helens volcanic plume in providing details of the dynamics and changing character of this major explosive eruption. Visible and thermal infrared (IR) data from a sequence of images at 30-min intervals from 0850 to 1720 Local Time (LT) give information on dispersal and plume top temperature. Initial visible and IR images at 0850 show the top of a spreading co-ignimbrite-like umbrella plume and an overshooting column emerging from it, both rising off the ground-hugging pyroclastic gravity flow generated by the opening directed blast. The overshooting column had a minimum temperature significantly colder than local ambient atmosphere, indicating substantial undercooling, and a maximum altitude of 31 +/- 2 km at 0920. This large plume system then formed a high-velocity, radially spreading, gravitationally driven current before becoming advected in the wind field at an average downwind velocity of 29 m/s. Reflectance values from visible GOES data change from lower to higher during periods of transition from darker toned Plinian to lighter toned co-ignimbrite plumes indicating that in this case satellite data resolved changes in eruptive style from plumes with a coarser to a finer dominant particle size.

Holasek, R. E.↗
DOE OSTI2022

Water‐Induced Diamond Formation at Earth's Core‐Mantle Boundary

Abstract The carbon and water cycles in the Earth's interior are linked to key planetary processes, such as mantle melting, degassing, chemical differentiation, and advection. However, the role of water in the carbon exchange between the mantle and core is not well known. Here, we show experimental results of a reaction between Fe 3 C and H 2 O at pressures and temperatures of the deep mantle and core‐mantle boundary (CMB). The reaction produces diamond, FeO, and FeH x , suggesting that water can liberate carbon from the core in the form of diamond (“core carbon extraction”) while the core gains hydrogen, if subducted water reaches to the CMB. Therefore, Earth's deep water and carbon cycles can be linked. The extracted core carbon can explain a significant amount of the present‐day mantle carbon. Also, if diamond can be collected by mantle flow in the region, it can result in unusually high seismic‐velocity structures.

Ko, Byeongkwan↗
NASA NTRS1993

Seasonal variability of bio-optical and physical properties in the Sargasso Sea

The seasonal variability of bio-optical and physical properties within the upper ocean at a site in the Sargasso Sea has been observed in multivariable moored systems during a 9-month period. In addition, complementary meteorological data, sea surface height and sea surface temperature maps, and expendable bathythermograph and shipboard profile data have been utilized for interpretation. The observations during March are characteristic of late wintertime conditions of a deep isothermal layer, but with intervening periods of warming due to the advection of warm outbreak waters associated with Gulf Stream meanders. The mixed layer depth shoals from greater than 160 m to about 25 m in late March (spring transition). Phytoplankton blooms follow the mixed layer shoaling. A succession of phytoplankton populations occurs during this transitional interval. The mixed layer remains near 25 m for the summer and deepens in mid-September. A relatively intense subsurface maximum in chlorophyll develops at about 75 m following the spring transition. The maximum persists, but weakens in mid-summer.

Dickey, T.↗