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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,513 records · Page 84

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NASA NTRS1991

A study of blade-vortex interaction sound generation and directionality

The directionality and strength of blade-vortex interactions (BVI) is explained through the radiation cone concept. BVI acoustic radiation is primarily the result of two sound mechanisms: the tip effect, and the radiation cone effect. The radiation cone effect is a highly directional mechanism which results when a lift distribution moves supersonically with respect to the fluid. After a physical explanation of the BVI mechanisms, sample cases using translating and rotating blades interacting with a straight line vortex are shown. The radiation cone concept is then applied to specific rotorcraft cases where it helps to explain zones of intense sound pressure level found in experimental results for the XV-15 tiltrotor and for a BO-105 helicopter scale model.

Ringler, Todd D.↗

DOE OSTI2022

The Role of Process-Directing Agents on Enamel Lesion Remineralization: Fluoride Boosters

The aim of this study was to investigate the effects of two process-directing agents (polyaspartic acid and osteopontin) used in a polymer-induced liquid-precursor (PILP) process on the remineralization of bacteria-induced enamel demineralization. Enamel demineralization lesions (depths of about 180–200 µm) were created and exposed to Streptococcus mutans, cultured with a 10% sucrose solution for 21 days, and remineralized using a PILP process (pH = 7.4, 14 days) with a calcium phosphate solution containing either polyaspartic acid or osteopontin in the presence or absence of fluoride (0.5 ppm). The specimens were examined under scanning electron microscopy. The fluoride was successfully incorporated into the PILP remineralization process for both polyaspartic acid and osteopontin. When the fluoride was added to the PILP remineralization solution, there was more uniform remineralization throughout the lesion than with either polyaspartic acid or osteopontin alone. However, in the absence of these process-directing agents, fluoride alone showed less remineralization with the formation of a predominantly surface-only layer. The PILP remineralization process relies on the ability of process-directing agents to stabilize calcium phosphate ions and holds promise for enamel lesion remineralization, and these agents, in the presence of fluoride, seem to play an important role as a booster or supplement in the continuation of remineralization by reducing the mineral gains at the surface layer.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2025

Sliding dynamics of skyrmion molecular crystals

Using both atomistic and particle-based simulations, we investigate the current-driven dynamics of skyrmions on two-dimensional periodic substrates when there are multiple skyrmions per substrate minimum. At zero drive, the system forms pinned skyrmion molecular crystal states consisting of dimers, trimers, or dimer-trimer mixtures that have both positional and orientational order. On a square substrate lattice, the motion above depinning occurs via a running soliton that travels completely transverse to the applied current. This motion is generated by a torque from the Magnus force, which rotates the n-mer states perpendicular to the applied current. At higher drives, the flow becomes disordered while the Hall angle diminishes and gradually approaches the intrinsic value. In some cases, we also find directional locking where the Hall angle becomes locked to certain symmetry directions of the substrate over a range of currents. The transitions into and out of directionally locked states are accompanied by negative differential mobility in which the net velocity decreases as the drive increases. In conclusion, on a triangular substrate, we find no transverse mobility effects, but still observe directionally locked motion.

36 MATERIALS SCIENCE↗

NASA NTRS1986

The influrence of an optical receiving system on statistical characteristics of a lidar signal

The effects connected with correlation of direct and backward waves propagating through the same randomly inhomogeneous media can be observed along the path with refection in a turbulent atmosphere. In particular, the mean intensity of the reflected wave can increase in comparison with the wave propagating in the forward direction at a doubled distance; the intensity fluctuations can become stronger. These effects depend on the strength of optical turbulence, as well as on the diffraction sizes of the exit apertures of the source and the reflector. However, the focusing of radiation reflected with a receiving telescope leads, in some cases, to the fact that the dependence of amplification effects on the parameters becomes essentially different. This should be taken into account when alayzing the lidar signals. The effect of backscattering amplification and amplification of the intensity fluctuations is discussed.

Zuev, A. E.↗

NASA NTRS1986

Comparison of two propeller source models for aircraft interior noise studies

The sensitivity of the predicted synchrophasing (SP) effectiveness trends to the propeller source model issued is investigated with reference to the development of advanced turboprop engines for transport aircraft. SP effectiveness is shown to be sensitive to the type of source model used. For the virtually rotating dipole source model, the SP effectiveness is sensitive to the direction of rotation at some frequencies but not at others. The SP effectiveness obtained from the virtually rotating dipole model is not very sensitive to the radial location of the source distribution within reasonable limits. Finally, the predicted SP effectiveness is shown to be more sensitive to the details of the source model used for the case of corotation than for the case of counterrotation.

Mahan, J. R.↗

NASA NTRS2003

Investigation of Aerodynamics Scale Effects for a Generic Fighter Configuration in the National Transonic Facility (Invited)

Two wind tunnel tests of a generic fighter configuration have been completed in the National Transonic Facility. The primary purpose of the tests was to assess Reynolds number scale effects on a thin-wing, fighter-type configuration up to full-scale flight conditions (that is, Reynolds numbers of the order of 60 million). The tests included longitudinal and lateral/directional studies at subsonic and transonic conditions across a range of Reynolds numbers from that available in conventional wind tunnels to flight conditions. Results are presented for three Mach numbers (0.6, 0.8, and 0.9) and three configurations: 1) Fuselage / Wing, 2) Fuselage / Wing / Centerline Vertical Tail / Horizontal Tail, and 3) Fuselage / Wing / Trailing-Edge Extension / Twin Vertical Tails. Reynolds number effects on the lateral-directional aerodynamic characteristics are presented herein, along with longitudinal data demonstrating the effects of fixing the boundary layer transition location for low Reynolds number conditions. In addition, an improved model videogrammetry system and results are discussed.

Tomek, W. G.↗

DOE OSTI2022

Decomposition of PVDF to delaminate cathode materials from end-of-life lithium-ion battery cathodes

The growing demand of electric vehicles and rapid consumption of rechargeable lithium-ion batteries (LIBs) require recycling of spent cathode active materials (CAMs) to reduce hazardous wastes and supply raw materials to LIB production. To separate CAMs from the cathode, direct calcination of polyvinylidene fluoride (PVDF) binder is widely applied, which leads to high energy consumption and release of toxic hydrogen fluoride. It is desirable to have an environmentally friendly and effective alternative to traditional direct calcination. In this study, five lithium salts, LiOAc (lithium acetate), LiNO 3 , LiCl, Li 2 CO 3 , and Li 2 SO 4 , were deployed and compared for their performance in recycling CAMs. A peel-off efficiency of up to 98.5% was achieved at a LiOAc to LiNO 3 molar ratio of 3:2, salt to cathode mass ratio of 10:1, and temperature of 300 °C at a holding time of 30 min. This system avoids corrosive chemicals and minimizes particle agglomeration of recycled products. Compared with sodium salt systems (NaOAc-NaNO 3 ) or direct calcination, the LiOAc-LiNO 3 system prevented high reaction temperature or further lithium loss and minimized crystal structure and morphological changes. In conclusion, a decomposition mechanism of PVDF through adsorption of HF and fluorine substitution was proposed.

25 ENERGY STORAGE↗

NASA NTRSDate not supplied

Comparison of Two Community Noise Models Applied to a NASA Urban Air Mobility Concept Vehicle

Predictions of community noise exposure from a NASA urban air mobility (UAM) concept vehicle have been conducted for representative operations using the FAA Aviation Environmental Design Tool (AEDT) in order to demonstrate modeling tool interoperability and assess applicability, capabilities and limitations of integrated noise modeling tools. To both quantify limitations and highlight other capabilities, a comparative analysis is performed using a time-domain simulation method, in particular, using the Volpe Advanced Acoustic Model (AAM). Using the same source noise model, the 3D directivity of a UAM concept vehicle is predicted in terms of aeroacoustic pressure time histories at a sphere of observer positions near the vehicle. In addition to distilling those data to a set of noise-power-distance data for input to AEDT, the data are processed preserving spectral directivity, into one-third and one-twelfth octave bands for input to AAM. Results from AEDT and AAM modeling are provided for a variety of metrics to demonstrate the effect that source noise directivity and propagation modeling fidelity have on predicted results at receptors over a study area.

urban air mobility↗

NASA NTRSDate not supplied

Comparison of Two Community Noise Models Applied to a NASA Urban Air Mobility Concept Vehicle

urban air mobility↗

NASA NTRS1975

Effects of geometric variables on the performance of a probe for direct measurement of free-steam stagnation pressure in supersonic flow

An investigation was conducted at Mach numbers of 1.41, 1.83, and 2.20 to determine the effects of parametric variations in the height of the pitot-tube center line from the probe surface and in the radius of the surface curvature on the pressure recovery of a probe designed to measure the free-stream stagnation pressure. The probe consists of a pitot tube mounted on the surface of a curved cylinder of circular cross section. The pitot tube senses the pressure of the stream tube which has been slowed by isentropic compression along the curved surface. Pressure recovery, greater than or equal to 99.8 percent of the free-stream stagnation pressure, was obtained for a wide range both of angle of attack and of yaw for probes satisfying the predetermined optimum design criteria.

Couch, L. M.↗

NASA NTRS1987

Convection and segregation in directional solidification of dilute and non-dilute binary alloys - Effects of ampoule and furnace design

A Petrov-Galerkin/finite-element method is used to analyze the effect of furnace configuration and ampoule design on the temperature field, the convection in the melt, the shape of the melt-solid interface, and the segregation of solute in the crystal, in the directional solidification of several dilute and nondilute binary semiconductor alloys. The vertical Bridgman-Stockbarger system leads to a two-cell flow structure, and the constant gradient furnace has only a single cell near the interface. Radial temperature gradients interact with the solute field to cause the previously predicted sideways diffusive instability, and addition of a solute that is less dense than the bulk melt and that is incorporated upon solidification decreases the intensity of the flow near the interface by increasing the melt density there. The present results have application to understanding of the effects on solute segregation of microgavity solidification and of applied magnetic fields.

Adornato, Peter M.↗

DOE OSTI2026

U-net architected deep material network training with microstructure local field information

The Deep Material Network (DMN) has recently emerged as a powerful reduced-order modeling framework for simulating the mechanical response of heterogeneous materials such as composites. Unlike most data-driven approaches that directly learn a material’s response under prescribed loading, the DMN acts as a homogenization operator, learning the kinematic constraints and mechanical interactions of the underlying microstructure. However, traditional DMN training relies exclusively on homogenized effective properties derived from Direct Numerical Simulations (DNS), discarding the rich local field data that govern microstructural interactions. In this work, we extend the DMN framework to incorporate such local field information into the offline training process. Utilizing a U-Net architecture, we augment the DMN training objective to include the first and second statistical moments of the local stress fields obtained from linear DNS. This ensures that the learned network topology not only fits the effective stiffness but also accurately reflects the internal local stress and strain partitioning of the microstructure. The results confirm that supervising the localization process during training yields a superior surrogate model, reducing local prediction errors by an order of magnitude and significantly improving generalization to unseen nonlinear constitutive behaviors compared to traditional DMNs.

36 MATERIALS SCIENCE↗

NASA NTRS2004

Solar Arrays for Direct-Drive Electric Propulsion: Arcing at High Voltages

The results from an experimental investigation to assess arcing during operation of high voltage solar arrays in a plasma environment are presented. The experiments were part of an effort to develop systems that would allow safe operation of Hall-Effect Thrustefls) in direct-drive mode. Arc discharges are generated when the array is biased negative with respect to the plasma. If sustained for long periods of time between adjacent solar cells, arcs may severely damage a solar array, thus significantly shortening its lifetime. Most often sustained arcs are triggered by plasma produced during short-duration discharge arcs (approximately 20 microseconds). These trigger arcs are sparked between the semiconducting cell and the covering dielectric. Both trigger and sustained (greater than 1 millisecond) arcs have been captured during the tests. Current and voltage waveforms associated with the different arc events are presented. The test results have defined operational limits (thresholds) for the various array concepts studied that minimize the likelihood of damage from sustained arcs. Experimental trends regarding the effect of the solar array substrate on arc duration are also presented.

Schneider, Todd A.↗

NASA NTRS2002

Effects of Microalloying on the Microstructures and Mechanical Properties of Directionally Solidified Ni-33(at.%)Al-31Cr-3Mo Eutectic Alloys Investigated

Despite nickel aluminide (NiAl) alloys' attractive combination of oxidation and thermophysical properties, their development as replacements for superalloy airfoils in gas turbine engines has been largely limited by difficulties in developing alloys with an optimum combination of elevated-temperature creep resistance and room-temperature fracture toughness. Alternatively, research has focused on developing directionally solidified NiAl-based in situ eutectic composites composed of NiAl and (Cr,Mo) phases in order to obtain a desirable combination of properties a systematic investigation was undertaken at the NASA Glenn Research Center to examine the effects of small additions of 11 alloying elements (Co, Cu, Fe, Hf, Mn, Nb, Re, Si, Ta, Ti, and Zr) in amounts varying from 0.25 to 1.0 at.% on the elevated-temperature strength and room-temperature fracture toughness of directionally solidified Ni-33Al-31Cr-3Mo eutectic alloy. The alloys were grown at 12.7 mm/hr, where the unalloyed eutectic base alloy exhibited a planar eutectic microstructure. The different microstructures that formed because of these fifth-element additions are included in the table. The additions of these elements even in small amounts resulted in the formation of cellular microstructures, and in some cases, dendrites and third phases were observed. Most of these elemental additions did not improve either the elevated-temperature strength or the room-temperature fracture toughness over that of the base alloy. However, small improvements in the compression strength were observed between 1200 and 1400 K when 0.5 at.% Hf and 0.25 at.% Ti were added to the base alloy. The results of this study suggest that the microalloying of Ni-33Al-31Cr-3Mo will not significantly improve either its elevatedtemperature strength or its room-temperature fracture toughness. Thus, any improvements in these properties must be acquired by changing the processing conditions.

Whittenberger, J. Daniel↗

DOE OSTI2023

High fidelity model of directed energy deposition: Laser-powder-melt pool interaction and effect of laser beam profile on solidification microstructure

Metal additive manufacturing technologies keep receiving a great deal of interest as well as strong requests to develop methods to link the process science to printed parts performance and understand how to overcome inherent limitations. Here, a high-fidelity model based on the multiphysics ALE3D code was developed to reproduce the directed energy deposition process down to the powder scale. This includes resolving the laser-powder-melt pool interactions (powder impingement and incorporation into melt pool, hydrodynamics flow condition and laser absorption inefficiencies) as well as the resulting solidification microstructure. This micrometer scale digital twin captured the effect of powder incorporation process and powder flow rate on porosity. Furthermore, it was used to explore how a ring laser beam profile instead of the standard Gaussian laser profile could decrease the thermal gradient along the solidification front in the melt pool, which in turn can increase propensity for more desirable equiaxed grains.

36 MATERIALS SCIENCE↗

NASA NTRS1999

Effects of Gravity on the Double-Diffusive Convection during Directional Solidification of a Non-Dilute Alloy with Application to the HgCdTe

General 2-D and 3-D finite element model of non-dilute alloy solidification was used to simulate growth of HgCdTe in terrestrial and microgravity conditions. Parametric research was undertaken to investigate effects of gravity level, gravity vector orientation and growth velocity on the pattern of melt convection, shape of crystal/melt interface and radial thermal gradient. Verification of the model was undertaken by comparison with previously published results. For low growth velocities plane front solidification occurs. The location and the shape of the interface was determined using melting temperatures obtained from the HgCdTe liquidus curve. The low thermal conductivity of the solid HgCdTe causes thermal short circuit through the ampoule walls, resulting in curved isotherms in the vicinity of the interface. Double-diffusive convection in the melt is caused by radial temperature gradients and by material density inversion with temperature. Cooling from below and the rejection at the solid-melt interface of the heavier HgTe-rich solute each tend to reduce convection. Because of these complicating factors dimensional rather then non-dimensional modeling was performed. For gravity levels higher then 10(exp -7) of terrestrial one it was found that the maximum convection velocity is extremely sensitive to gravity vector orientation and can be reduced at least by 50% by choosing proper orientation of the ampoule. The predicted interface shape is in agreement with one obtained experimentally by quenching.

Bune, Andris↗

NASA NTRS2010

Space Life Sciences Directorate's Position on the Physiological Effects of Exposing the Crewmemeber to Low-Voltage Electrical Hazards During Extravehicular Activity

The models predict that, for low voltage exposures in the space suit, physiologically active current could be conducted across the crew member causing catastrophic hazards. Future work with Naval Health Research Center Detachment Directed Energy Bio-effects Laboratory is being proposed to analyze additional current paths across the human torso and upper limbs. These models may need to be verified with human studies.

Hamilton, Douglas↗

NASA NTRS2008

Jet Penetration into a Scaled Microfabricated Stirling Cycle Regenerator

The cooler and heater adjacent to the regenerator of a Stirling cycle engine have tubes or channels which form jets that pass into the regenerator while diffusing within the matrix. An inactive part of the matrix, beyond the cores of these jets, does not participate fully in the heat transfer between the flow of working fluid and the regenerator matrix material, weakening the regenerator s ability to exchange heat with the working fluid. The objective of the present program is to document this effect on the performance of the regenerator and to develop a model for generalizing the results. However, the small scales of actual Stirling regenerator matrices (on the order of tens of microns) make direct measurements of this effect very difficult. As a result, jet spreading within a regenerator matrix has not been characterized well and is poorly understood. Also, modeling is lacking experimental verification. To address this, a large-scale mockup of thirty times actual scale was constructed and operated under conditions that are dynamically similar to the engine operation. Jet penetration with round jets and slot jets into the microfabricated regenerator geometry are then measured by conventional means. The results are compared with those from a study of spreading of round jets within woven screen regenerator for further documentation of the comparative performance of the microfabricated regenerator geometry.

Sun, Liyong↗