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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Phenylethynyl Terminated Arylene Ether Oxadiazole and Triazole Oligomers and Their Cured Polymers

Several novel phenylethynyl terminated arylene ether oligomers containing oxadiazole and triazole rings were prepared as part of an effort to develop high performance polymers with an attractive combination of properties (e.g. processability and mechanical performance) for future NASA applications. The oligomers displayed low melt viscosities and good solubilities. Thin films cast from solutions of the oligomers and cured for one hour at 350 C in air gave good tensile properties. Titanium to titanium (6Al-4V) tensile shear specimens were readily fabricated and provided moderate strengths. The chemistry and properties of these new materials are discussed.

Thompson, C. M.↗
DOE OSTI2021

Modeling and simulation of transitional Rayleigh–Taylor flow with partially averaged Navier–Stokes equations

In this work, the partially averaged Navier–Stokes (PANS) equations are used to predict the variable-density Rayleigh–Taylor (RT) flow at Atwood number 0.5 and maximum Reynolds number 500. This is a prototypical problem of material mixing, featuring laminar, transitional, and turbulent flow, instabilities and coherent structures, density fluctuations, and production of turbulence kinetic energy by both shear and buoyancy mechanisms. These features pose numerous challenges to modeling and simulation, making the RT flow ideal to develop the validation space of the recently proposed PANS Besnard–Harlow–Rauenzahn-linear eddy viscosity model closure. The numerical simulations are conducted at different levels of physical resolution and test three approaches to set the parameters $f_\phi$ defining the range of physically resolved scales. The computations demonstrate the efficiency (accuracy vs cost) of the PANS model predicting the spatiotemporal development of the RT flow. Results comparable to large-eddy simulations and direct numerical simulations are obtained at significantly lower physical resolution without the limitations of the Reynolds-averaged Navier–Stokes equations in these transitional flows. The data also illustrate the importance of appropriate selection of the physical resolution and the resolved fraction of each dependent quantity $\phi$ of the turbulent closure, $f_\phi$. These two aspects determine the ability of the model to resolve the flow phenomena not amenable to modeling by the closure and, as such, the computations’ fidelity.

Navier Stokes equations↗
DOE OSTI2021

Electric field and turbulence in global Braginskii simulations across the ASDEX Upgrade edge and scrape-off layer

Turbulence simulations in diverted geometry across the edge and scrape-off layer (SOL) of ASDEX Upgrade are performed with the GRILLIX code (Stegmeir et al 2019 Phys. Plasmas 26 052517). The underlying global (full-f) drift-reduced Braginskii model allows to concurrently study the self-consistent dynamics of the turbulence and the background as well as the evolution of toroidal and zonal flows. Different contributions to the radial electric field are identified. The dominant contribution on closed flux surfaces comes from the ion pressure gradient, due to the diamagnetic drift in the curved magnetic field. Large deviations can be induced, in particular, by the polarization particle flux, leading to zonal flows. The latter are driven by small-scale eddies, but do not exhibit much impact on the overall transport which is driven by ballooning modes at larger scales. Ion viscosity is found to be important in damping poloidal rotation through adjusting of the parallel velocity profile, but not via direct vorticity damping. The zonal flow drive peaks at the separatrix, where a strong shear layer forms due to the sheath-induced counter-propagating SOL flow, allowing for the formation of a transport barrier. The temperature profile across the separatrix is determined by the competition between cross-field transport and outflow in the SOL, the latter being largely controlled by the parallel heat conductivity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Mixing in Low Reynolds Number Reacting Impinging Jets in Crossflow

Previous efforts to model uranyl fluoride formation in an impinging jet gas reactor underpredicted spatial mixing and overpredicted chemical conversion into particulates. The previous fluid dynamics model was based on the solution of the Reynolds Averaged Navier Stokes equations. After simulating fluid dynamics, aerosol dynamics were superimposed onto CFD-simulated gas reactant species concentrations. The current work explores the influence of complex unsteady flow features on the overall flow physics and chemistry for a low Reynolds number, opposed flow, impinging jet gas reactor where there is a low Reynolds number cross flow. The objective of this study was to assess the impact of model formulation on scalar mixing and transport. Here, transient flow simulations were performed using Scale Resolving Simulations. Large-Eddy Simulations with the dynamic Smagorinsky turbulence model were performed along with simulations which directly resolved the flow. Average and root-mean-square (RMS) velocities and species concentrations were computed along with modeled and resolved turbulence kinetic energy (TKE), modeled turbulence dissipation, and modeled turbulent viscosity. Lagrangian flow tracers were also used to quantify species concentrations along path lines emanating from the jet tips. Transient simulation data were compared to results from RANS simulations using the k-ω shear stress transport (SST) model and Reynolds Stress Model (RSM). Transient simulations showed spatial mixing patterns which were more consistent with experimental data and helped elucidate the process of particle formation observed in experiments.

42 ENGINEERING↗
DOE OSTI2021

Dynamic flow stress of pure polycrystalline aluminum: Pressure-shear plate impact experiments and extension of dislocation-based modeling to large strains

The dynamic thermo-mechanical behavior of pure aluminum has attracted renewed interest lately due to experimental observations of an anomalous increase in Hugoniot Elastic Limit (HEL) at incipient plasticity and elevated temperatures in polycrystalline pure metals. In context of current dislocation-mediated plasticity models for metals, this increase in dynamic strength is indicative of a transition in the rate controlling mechanism for dislocation glide from being thermally assisted to phonon-drag restricted due to increase in phonon viscosity at elevated temperatures. Though these studies have helped to shed light on these important mechanisms operative in FCC metals at incipient plasticity, the extent to which they contribute to flow stress, particularly at larger strains, remains unclear. Here, we address these questions through a combined experimental and modeling effort focused on investigating the evolution of dynamic flow stress in polycrystalline aluminum using experimental data gathered from a series of combined pressure-and-shear plate impact (PSPI) experiments designed to reveal the flow stress of pure aluminum at strain rates ~ 10 5 /s, plastic strains of up to 40% and temperatures ranging from room to 866 K. In all cases, the flow stress of aluminum, as inferred from the measured transverse particle velocity histories at the free surface of an elastic tungsten carbide target plate, reveals saturation with increasing plastic strains at stress levels that decrease with increasing test temperatures. Numerical simulations are performed to correlate the experimentally observed temperature and strain rate dependence of flow stress at small and large plastic strains using the Austin-McDowell dislocation-mediated plasticity model parametrized to normal plate impact experiments conducted in an earlier study by Zaretsky and Kanel (2012). Extensions to the model are made to better represent dynamic behavior of pure aluminum at larger plastic strains as observed in elevated temperature split Hopkinson Pressure bar (SPHB) experiments of Samanta (1971) and Lindholm and Yeakly (1965), and the combined pressure-and-shear plate-impact experiments conducted in the present study. The main theoretical extension to the Austin-McDowell model made in this paper is the introduction of a new rate- and temperature- dependent dynamic recovery function, which can potentially allow for an effective reduction in the rate of accumulation of dislocations at large plastic strains. The numerical predictions of the revised and re-calibrated plasticity model are brought into agreement with the experimental observations, correlating sufficiently well with dynamic yield stress at incipient plasticity and the flow stress levels at larger plastic strains, plastic strain rates in the range 10 3 – 10 6 /s, and elevated temperatures up to near melt. The model, in concert with the experimental measurements, suggests that at incipient plasticity the rate governing mechanism for plastic flow is phonon-drag restricted dislocation glide, whereas, at higher magnitudes of plastic strain, it transitions to stress-assisted thermally activated glide. The transition between these two rate governing mechanisms is controlled by the evolution of dislocations throughout the deformation process.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Superrotation planetary atmospheres: Mechanical analogy, angular momentum budget and simulation of the spin up process

Superrotation rates observed in planetary atmospheres are analyzed based on the concept of a thermally driven zonally symmetric circulation. Specifically, how this superrotation is produced and maintained against the tendency for friction to oppose differential motions between the atmosphere and the underlying planet is addressed. The time evolution of a fluid leading from corotation under uniform heating to superrotation under globally nonuniform heating is simulated using a three dimensional zonally symmetric spectral model and Laplace transformation. The increased tendency toward geostrophy combined with the increase of surface pressure toward the poles (due to meridional mass transport), induces the atmosphere to subrotate temporarily at lower altitudes. The resulting viscous shear near the surface thus permits angular momentum to flow from the planet into the atmosphere where it propagates upwards and, combined with the change in moment of inertia, produces large superrotation rates at higher viscosities.

Mayr, H. G.↗
NASA NTRS1993

A simplified Reynolds stress model for unsteady turbulent boundary layers

A simplified Reynolds stress model has been developed for the prediction of unsteady turbulent boundary layers. By assuming that the net transport of Reynolds stresses is locally proportional to the net transport of the turbulent kinetic energy, the time dependent full Reynolds stress model is reduced to a set of ordinary differential equations. These equations contain only time derivatives and can be readily integrated in a time dependent boundary layer or Navier-Stokes code. The turbulent kinetic energy and dissipation rate needed for the model are obtained by solving the k-epsilon equations. This simplified Reynolds stress turbulence model (SRSM) does not use the eddy viscosity assumption, which may not be valid for unsteady turbulent flows. The anisotropy of both the steady and the unsteady turbulent normal stresses can be captured by the SRSM model. Through proper damping of the shear stresses, the present model can be used in the near wall region of turbulent boundary layers. This model has been validated against data for steady and unsteady turbulent boundary layers, including periodic turbulent boundary layers subjected to a mean adverse pressure gradient. For the cases tested, the predicted unsteady velocity and turbulent stress components agree well with the experimental data. Comparison between the predictions from the SRSM model and a k-epsilon model is also presented.

Fan, Sixin↗
NASA NTRS2024

Characterization of NUW-LHT-5m, A Lunar Highland Simulant

A new simulant of the lunar highlands regolith, NUW-LHT-5M, was designed by NASA and manufactured by Washington Mills. The simulant was based on Apollo 16 data and is a member of the NU-LHT-series. NASA’s Marshall Space Flight Center and Johnson Space Center have already purchased 3 metric tons of the simulant for advanced engineering work. In support of engineering uses of the simulant, we provided measurements of the simulant including: mineral abundance and composition, liberation, X-ray fluorescence (XRF), ferrous iron, carbon, sulfur, 60 element inductively coupled plasma (ICP), loss on ignition, particle size, both 2D and 3D particle shape, specific surface area, shear, cohesion, internal friction, helium pycnometry, minimum index density, tap density, magnetic susceptibility, cryogenic and high temperature permittivity, visible and near-infrared (VNIR) and middle infra-red spectroscopy (MIR), differential scanning calorimetry (DSC), viscosity, thermal diffusivity, thermal conductivity, thermal gravimetric analysis (TGA), evolved gas analysis (EGA), and spark sintering. For the crystalline components the design of the simulant called for two rocks from the Stillwater Complex, Montana: 17.6 wt% norite, 37.7% anorthosite, and 4.7 wt% olivine from an unspecified commercial source. The other 40% of the simulant was a high calcium (An100), vesicular glass that Washington Mills made specifically for the simulant. Fabrication and quality control processes for both the glass and the simulant are described. Importantly, most of the graphs and tables presented herein provide values for both the new simulant and data for the older NASA mare simulant, JSC-1A. Finally, we discussed the current limitations of NUW-LT-5M and most other lunar regolith simulants to replicate the lunar material.

lunar regolith simulant↗
DOE OSTI2020

Turbulence model reduction by deep learning

A defining problem of turbulence theory is to produce a predictive model for turbulent fluxes. These have profound implications for virtually all aspects of the turbulence dynamics. In magnetic confinement devices, drift-wave turbulence produces anomalous fluxes via cross-correlations between fluctuations. In this work, we introduce an alternative, data-driven method for parametrizing these fluxes. The method uses deep supervised learning to infer a reduced mean-field model from a set of numerical simulations. We apply the method to a simple drift-wave turbulence system and find a significant new effect which couples the particle flux to the local gradient of vorticity. Notably, here, this effect is much stronger than the oft-invoked shear suppression effect. We also recover the result via a simple calculation. The vorticity gradient effect tends to modulate the density profile. In addition, our method recovers a model for spontaneous zonal flow generation by negative viscosity, stabilized by nonlinear and hyperviscous terms. We highlight the important role of symmetry to implementation of the new method.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1989

Similarity solutions of jet flows using a multiple-scale turbulence model

An accurate finite difference scheme is used to study the performance of a newly developed multiple-scale turbulence model in the similarity region of plane/radial/round jet flows. Under the assumption that molecular viscosity can be neglected, the governing equations contain a hidden eigenvalue which corresponds to the sharp boundary of the flowfield. It is found that this eigenvalue is the locus of the free boundary separating the turbulent shear flow and the irrotational ambient fluid.

Chen, C. P.↗
NASA NTRS1985

Features of a reattaching turbulent shear layer in divergent channel flow

Experimental data have been obtained in an incompressible turbulent flow over a rearward-facing step in a diverging channel flow. Mean velocities, Reynolds stresses, and triple products that were measured by a laser Doppler velocimeter are presented for two cases of tunnel wall divergence. Eddy viscosities, production, convection, turbulent diffusion, and dissipation (balance of kinetic energy equation) terms are extracted from the data. These data are compared with various eddy-viscosity turbulence models. Numerical calculations incorporating the k-epsilon and algebraic-stress turbulence models are compared with the data. When determining quantities of engineering interest, the modified algebraic-stress model (ASM) is a significant improvement over the unmodified ASM and the unmodified k-epsilon model; however, like the others, it dramatically overpredicts the experimentally determined dissipation rate.

Driver, D. M.↗
NASA NTRS1985

Experimental study of a three-dimensional, shear-driven, turbulent boundary layer using a three-dimensional laser Doppler velocimeter

Experimental data have been obtained in a three-dimensional, shear-driven, turbulent boundary layer subjected to sudden transverse strain. Measurements made with a newly developed, three-dimensional laser Doppler velocimeter include all components of mean flow, turbulent Reynolds stresses, and triple-product correlations. Eddy viscosities, production, convection, turbulent diffusion, and dissipation (balance of kinetic energy equation) are extracted from the data. It was shown experimentally that eddy viscosity is strongly direction-dependent (not a scalar), indicating a need for full Reynolds stress modeling. Turbulence models for eddy viscosity, stress diffusion, pressure rate-of-strain, and anisotropy of Reynolds stresses are tested using the data. Calculations using a Reynolds stress equation model are compared with the data.

Driver, D. M.↗
NASA NTRS1996

Axisymmetric Two-Dimensional Computation of Magnetic Field Dragging in Accretion Disks

In this paper we model a geometrically thin accretion disk interacting with an externally imposed, uniform, vertical magnetic field. The accretion flow in the disk drags and distorts field lines, amplifying the magnetic field in the process. Inside the disk the radial component of the field is sheared into a toroidal component. The aim of this work is to establish the character of the resultant magnetic field and its dependence on the disk's parameters. We concentrate on alpha-disks driven by turbulent viscosity. Axisymmetric, two-dimensional solutions are obtained without taking into account the back-reaction of the magnetic field on the structure of the disk. The character of the magnetic field depends strongly on the magnitude of the magnetic Prandtl number, P . We present two illustrative examples of viscous disks: a so-called 'standard' steady state model of a disk around a compact star (e.g., cataclysmic variable), and a steady state model of a proto-planetary disk. In both cases, P = 1, P = 10(sup -1), and P = 10(sup -2) scenarios are calculated. Significant bending and magnification of the magnetic field is possible only for disks characterized by P of the order of 10(sup -2). In such a case, the field lines are bent sufficiently to allow the development of a centrifugally driven wind. Inside the disk the field is dominated by its toroidal component. We also investigate the dragging of the magnetic field by a nonviscous protoplanetary disk described by a phenomenological model. This scenario leads to large distortion and magnification of the magnetic field.

Reyes-Ruiz, Mauricio↗
NASA NTRSDate not supplied

Surveillance for Jugular Venous Thrombosis in Long-Duration Space Flight: Findings From Twenty-Eight U.S. Astronauts

BACKGROUND: Given the high incidence of internal jugular vein (IJV) flow anomalies aboard the International Space Station and a case of thrombosis, the National Aeronautics and Space Administration (NASA) instituted an occupational surveillance program to evaluate astronauts for venous thromboembolism (VTE). Current findings of the program are presented. METHODS: NASA astronauts undergo pre- and in-flight VTE surveillance examinations using a standardized vascular ultrasound protocol, which includes evaluation for bilateral IJV compressibility, filling, flow, and spontaneous echo contrast (SEC). RESULTS: Twenty-eight NASA astronauts had terrestrial baseline examinations and at least one in-flight imaging session. The reduction of in-flight peak IJV flow speeds was significant and more pronounced on the left. Comparing the first in-flight measurement to the terrestrial baseline, peak flow speeds were reduced from 90.1±41.9 cm/s (average ±SD) to 62.1±31.6 cm/s on the right and from 76.9±41.8 cm/s to 26.8±18.2 cm/s on the left. Seven astronauts showed stagnant or retrograde flow in the left IJV. Fourteen developed appreciable SEC in the left IJV (7 greater than mild); none developed significant right-sided SEC. All IJVs were fully compressible and free from thrombi. DISCUSSION: Bilateral IJV flow speed reduction is observed in microgravity, possibly due to the multitude of available flow redistribution paths for cranial drainage. In a subset of astronauts, significant flow anomalies develop that may facilitate thrombus formation through changes in blood viscosity and speed, especially if combined with other thrombogenic factors. These findings warrant attention to the interplay between individual vascular configurations and the dynamic properties of blood as a non-Newtonian fluid in the reduced-shear flow environment of microgravity.

Ashot Sargsyan↗
DOE OSTI2025

Improved pressure-gradient sensor for the prediction of separation onset in RANS models

Here, we improve upon two key aspects of the Menter shear stress transport (SST) turbulence model: (1) We propose a more robust adverse pressure gradient sensor based on the strength of the pressure gradient in the direction of the local mean flow; (2) We propose two alternative eddy viscosity models to be used in the adverse pressure gradient regions identified by our sensor. Direct numerical simulations of the Boeing Gaussian bump are used to identify the terms in the baseline SST model that need correction, and a posteriori Reynolds-averaged Navier-Stokes calculations are used to calibrate coefficient values, leading to a model that is both physics driven and data informed. The two sensor-equipped models are applied to two thick airfoils representative of modern wind turbine applications, the FFA-W3-301 and the DU00-W-212. The proposed models improve the prediction of stall (onset of separation) with respect to the prediction of the baseline SST model.

17 WIND ENERGY↗
NASA NTRS1978

Rheology of composite solid propellants during motor casting

In a study conducted to evaluate flow parameters of uncured solid composite propellants during motor casting, two motors (1.8M-lb grain wt) were cast with a PBAN propellant exhibiting good flow characteristics in a 260-in. dia solid rocket motor. Attention is given to the effects of propellant compositional and processing variables on apparent viscosity as they pertain to rheological behavior and grain defect formation during casting. It is noted that optimized flow behavior is impaired with solid propellant loading. Non-Newtonian pseudoplastic flow is observed, which is dependent upon applied shear stress and the age of the uncured propellant.

Rogers, C. J.↗
NASA NTRS1982

Features of a reattaching turbulent shear layer subject to an adverse pressure gradient

Experimental data have been obtained in an incompressible turbulent flow over a rearward-facing step with superimposed adverse pressure gradient. Mean velocities, Reynolds stresses and triple-products measured by a laser Doppler velocimeter are presented for two cases of adverse pressure gradient. Mixing lengths, eddy viscosities, production, convection, turbulent diffusion, and dissipation terms are extracted from the data. These data are compared with various mixing length and eddy-viscosity turbulence models. Numerical calculations incorporating the k-epsilon and the algebraic-stress turbulence models are compared with the data. When determining quantities of engineering interest, the modified algebraic-stress model (ASM) is a significant improvement over the unmodified ASM and the unmodified k-epsilon model

Driver, D. M.↗
NASA NTRS1983

Measurement of the linear viscoelastic behavior of antimisting kerosene

Measurements of dynamic viscoelastic properties in very small oscillating shear deformations was made on solutions of a jet fuel, Jet A, containing an antimisting polymeric additive, FM-9. A few measurements were also made on solutions of FM-9 in a mixed solvent of mineral oil, Tetralin, and 0-terphenyl. Two samples of FM-9 had approximate number-average molecular weights of 12,000,000 and 8,100,000 as deduced from analysis of the measurements. The ranges of variables were 2.42 to 4.03 g/1 in concentration (0.3 to 0.5% by weight), 1 to 35 in temperature, 1.3 to 9.4 cp in solvent viscosity, and 103 to 6100 Hz in frequency. Measurements in the Jet A solvent were made both with and without a modifying carrier. The results were compared with the Zimm theory and the viscoelastic behavior was found to resemble rather closely that of ordinary non-polar polymers in theta solvents. The relation of the results to the antithixotropic behavior of such solutions a high shear rates is discussed in terms of intramolecular and intermolecular interactions.

Ferry, J. D.↗