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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

SimUAM: A Comprehensive Microsimulation Toolchain to Evaluate the Impact of Urban Air Mobility in Metropolitan Areas

Over the past several years, Urban Air Mobility (UAM) has galvanized enthusiasm from investors and researchers, marrying expertise in aircraft design, transportation, logistics, artificial intelligence, battery chemistry, and broader policymaking. However, two significant questions remain unexplored: (1) What is the value of UAM in a region’s transportation network? and (2) How can UAM be effectively deployed to realize and maximize this value to all stakeholders, including riders and local economies? To adequately understand the value proposition of UAM for metropolitan areas, the authors develop a holistic multi-modal toolchain, SimUAM, to model and simulate UAM and its impacts on travel behavior. This toolchain has several components: (1) Microsimulation Analysis for Network Traffic Assignment (MANTA): A fast, high-fidelity regional-scale traffic microsimulator, (2) VertiSim: Agranular, discrete-event vertiport and pedestrian simulator, (3) Flexible Engine for Fast-time Evaluation of Flight Environments (Fe3): A high-fidelity, trajectory-based aerial microsimulation. SimUAM, rooted in granular, GPU-based microsimulation, models millions of trips and their movements in the street network and in the air, producing interpretable and actionable performance metrics for UAM designs and deployments. Once the ground-air interface is modeled, the authors find that the market for UAM decreases across all network designs relative to models with static assumptions about transfer times. However, significant improvements can be made to balance the demand and optimize the networks for transfer time, likely increasing the number of benefited trips. The modularity, extensibility, and speed of the platform will allow for rapid scenario planning and sensitivity analysis, effectively acting as a detailed performance assessment tool.

urban air mobility↗
NASA NTRS1992

Heat transfer characteristics of hypersonic waveriders with an emphasis on the leading edge effects

The heat transfer characteristics in surface radiative equilibrium and the aerodynamic performance of blunted hypersonic waveriders are studied along two constant dynamic pressure trajectories for four different Mach numbers. The inviscid leading edge drag was found to be a small (4 to 8 percent) but not negligible fraction of the inviscid drag of the vehicle. Although the viscous drag at the leading edge can be neglected, the presence of the leading edge will influence the transition pattern of the upper and the lower surfaces and therefore affect the viscous drag of the entire vehicle. For an application similar to the National Aerospace Plane (NASP), the present study demonstrates that the waverider remains a valuable concept at high Mach numbers if a state-of-the-art active cooling device is used along the leading edge. At low Mach number (less than 5), the study shows the surface radiative cooling might be sufficient. In all cases, radiative cooling is sufficient for the upper and lower surfaces of the vehicle if ceramic composites are used as thermal protection.

Vanmol, Denis O.↗
DOE OSTI2024

Dynamic density functional theory of polymers with salt in electric fields

Here we present a dynamic density functional theory for modeling the effects of applied electric fields on the local structure of polymers with added salt (polymer electrolytes). Time-dependent equations for the local electrostatic potential and volume fractions of polymer, cation, and anion of added salt are developed using the principles of linear irreversible thermodynamics. For such a development, a field theoretic description of the free energy of polymer melts doped with salts is used, which captures the effects of local variations in the dielectric function. Connections of the dynamic density functional theory with experiments are established by relating the three phenomenological Onsager’s transport coefficients of the theory to the mutual diffusion of electrolyte, ionic conductivity, and transference number of one of the ions. The theory is connected with a statistical mechanical model developed by Bearman and Kirkwood [J. Chem. Phys. 28, 136 (1958)] after relating the three transport coefficients to friction coefficients. The steady-state limit of the dynamic density functional theory is used to understand the effects of dielectric inhomogeneity on the phase separation in polymer electrolytes. The theory developed here provides not only a way to connect with experiments but also to develop multi-scale models for studying connections between local structure and ion transport in polymer electrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

Nongray gas analyses for reflecting walls utilizing a flux technique

A flux formulation for a planar slab of molecular gas radiation bounded by diffuse reflecting walls is developed. While this formulation is limited to the planar geometry, it is useful for studying approximations necessary in modeling nongray radiative heat transfer. The governing equations are derived by considering the history of multiple reflections between the walls. Accurate solutions are obtained by explicitly accounting for a finite number of reflections and approximating the spectral effects of the remaining reflections. Four approximate methods are presented and compared using a single absorption band of H2O. All four methods reduce to an identical zeroth-order formulation, which accounts for all reflections approximately but does handle nonreflected radiation correctly. A single absorption band of CO2 is also considered using the best-behaved approximation for higher orders. A zeroth-order formulation is sufficient to predict the radiative transfer accurately for many cases considered. For highly reflecting walls, higher order solutions are necessary for better accuracy. Including all the important bands of H2O, the radiative source distributions are also obtained for two different temperature and concentration profiles.

Menart, J. A.↗
NASA NTRS1973

An analysis of a charring ablator with thermal nonequilibrium, chemical kinetics, and mass transfer

The differential equations governing the transient response of a one-dimensional ablative thermal protection system are presented for thermal nonequilibrium between the pyrolysis gases and the char layer and with finite rate chemical reactions occurring. The system consists of three layers (the char layer, the uncharred layer, and an optical insulation layer) with concentrated heat sinks at the back surface and between the second and third layers. The equations are solved numerically by using a modified implicit finite difference scheme to obtain solutions for the thickness of the charred and uncharred layers, surface recession and pyrolysis rates, solid temperatures, porosity profiles, and profiles of pyrolysis-gas temperature, pressure, composition, and flow rate. Good agreement is obtained between numerical results and exact solutions for a number of simplified cases. The complete numerical analysis is used to obtain solutions for an ablative system subjected to a constant heating environment. Effects of thermal, chemical, and mass transfer processes are shown.

Clark, R. K.↗
NASA NTRS2004

Modeling Compressibility Effects in High-Speed Turbulent Flows

Man has strived to make objects fly faster, first from subsonic to supersonic and then to hypersonic speeds. Spacecraft and high-speed missiles routinely fly at hypersonic Mach numbers, M greater than 5. In defense applications, aircraft reach hypersonic speeds at high altitude and so may civilian aircraft in the future. Hypersonic flight, while presenting opportunities, has formidable challenges that have spurred vigorous research and development, mainly by NASA and the Air Force in the USA. Although NASP, the premier hypersonic concept of the eighties and early nineties, did not lead to flight demonstration, much basic research and technology development was possible. There is renewed interest in supersonic and hypersonic flight with the HyTech program of the Air Force and the Hyper-X program at NASA being examples of current thrusts in the field. At high-subsonic to supersonic speeds, fluid compressibility becomes increasingly important in the turbulent boundary layers and shear layers associated with the flow around aerospace vehicles. Changes in thermodynamic variables: density, temperature and pressure, interact strongly with the underlying vortical, turbulent flow. The ensuing changes to the flow may be qualitative such as shocks which have no incompressible counterpart, or quantitative such as the reduction of skin friction with Mach number, large heat transfer rates due to viscous heating, and the dramatic reduction of fuel/oxidant mixing at high convective Mach number. The peculiarities of compressible turbulence, so-called compressibility effects, have been reviewed by Fernholz and Finley. Predictions of aerodynamic performance in high-speed applications require accurate computational modeling of these "compressibility effects" on turbulence. During the course of the project we have made fundamental advances in modeling the pressure-strain correlation and developed a code to evaluate alternate turbulence models in the compressible shear layer.

Sarkar, S.↗
DOE OSTI2024

Polyamide-Based Ion Exchange Membranes: Cation-Selective Transport through Water Purification Membranes

Ion-selective membranes are necessary components of many electrochemical systems including fuel cells, electrolyzers, redox flow batteries, and electrodialyzers. Perfluorinated sulfonated membranes (PFSMs) dominate these applications due to their excellent combination of fast ion transport, stability, and processability. However, perfluorinated cation exchange membranes (CEMs) are expensive, and their production process involves chemistry that generates toxic perfluorinated chemicals. The development of affordable, nonfluorinated membranes with a competitive combination of high ion selectivity, transport, and stability could help enable the widespread use of the technologies listed above while hastening the development of emerging electrochemical systems, including aqueous alkaline CO 2 sorbent regeneration. To this end, we pursue the use of thin-film composite polyamide (PA-TFCs) membranes–those that typically find application in reverse osmosis and nanofiltration desalination–as cation-selective exchange membranes. Given their negative surface charge under neutral-to-alkaline conditions, PA-TFCs can serve as effective CEMs in these pH regimes. We prepared a series of PA-TFCs from traditional monomers (trimesoyl chloride and piperazine) and compared their thicknesses, charge densities, water transport properties, ion transport properties, and long-term stability in a high pH environment to traditional CEMs (Nafion and FKE) and commercial nanofiltration and reverse osmosis membranes. We find that some of the best-performing PA-TFC membranes have similar resistances and Na + transference numbers compared to Nafion 117 in Na 2 SO 4 and NaHCO 3 -containing solutions. This proof-of-principle study suggests that further optimization of PA-TFCs could enable cost-effective ion exchange membrane alternatives to PFSMs.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Analysis and prediction of reaction kinetics using the degree of rate control

“Degree of rate control” (DRC) analysis provides a quantitative approach for analysing the kinetics of multi-step reaction mechanisms that has been widely applied to both heterogeneous and homogeneous catalysis research, as well as electrocatalysis. The DRC of any given transition state or intermediate is defined as a partial derivative such that it approximately equals the fractional increase in net rate to the product of interest per differential decrease in its standard-state free energy for that species (÷RT), holding constant the standard-state free energies of all other transition states and intermediates. Even very complex mechanisms usually have only a few species with non-zero DRCs and are thus the species whose interactions with the catalyst most strongly affect the net rate. These key DRC values thus offer a simple and intuitive route to optimize catalyst materials, especially with the assistance of computational methods like density functional theory (DFT). These high-DRC species are also the species whose energetics must be most accurately measured or calculated to achieve an accurate kinetic model for any reaction mechanism. In simple cases with a single “rate-determining step”, the DRC for its transition state (TS) is + 1. Catalyst-bound intermediates, on the other hand, often have negative DRCs equal to a small integer times their fractional occupancy of catalyst sites. The apparent activation energy equals a weighted average of the standard-state enthalpies (relative to reactants) of all the species (intermediates, transition states and products) in the reaction mechanism, each weighted by its DRC (+RT). It has been shown that the apparent transfer coefficient in electrocatalysis, an inverted form of the Tafel slope, is a weighted average of the number of electrons transferred to generate each intermediate or product species in the mechanism, weighted again by the DRC. Quantitative analysis of kinetic isotope effects (KIEs, or the ratio of net rates for different reactant isotopes) in complex mechanisms has shown that the logarithm of the KIE equals the weighted average over all species in the mechanism of the difference between the two isotopes in their standard-state free energies (÷RT), again weighted by the DRC. The reaction orders with respect to fluid-phase concentrations of reactants, products and intermediates have also been proven to be directly related to DRCs. Thus, there are numerous experimental observables which equate to short linear combinations of DRCs, so that combinations of experimental measurements might provide access to DRC values. Since its invention for transition states in 1994 and its generalization to include intermediates in 2009, the DRC has thus far mainly been calculated for microkinetic models based either entirely on DFT or on DFT with the key energies (i.e., those for high-DRC species) being fine-tuned to match experiments. The relationships summarized in this work provide new opportunities for using experiments earlier in the development and optimization of microkinetic models that require input from computational catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Modulating physicochemical interfaces enables li-rich oxides based ceramic solid-state li batteries under ambient conditions

Li-rich layered oxides exhibit promising potential applications in high-energy-density solid-state lithium metal batteries. Nevertheless, the strong oxidative oxygen species generate at high voltage, which poses great challenges to positive electrode-side interface stability. Herein, a robust in-situ polymerization gel polymer electrolyte with bifunctional additives is designed for interface modification. These additives, include lithium difluoro(oxalate) borate and LiPO 2 F 2 , regulate the Li + chemical environment in gel polymer electrolyte to enhance crosslink density without residual oligomer, which reduce gas generation and suppress contact loss, thus avoiding interfacial impedance divergence. Concurrently, the designed gel polymer electrolyte enables a wide electrochemical stability window (up to 4.7 V) and a high Li + transference number (0.82). Additionally, the additives induced F- and B-rich inorganic cathode-electrolyte interphase inhibits side reactions and oxygen/transition metal loss effectively, stabilizing the chemical interface. The as-constructed Li-rich layered oxides-based ceramic solid-state lithium metal batteries with gel polymer electrolyte interface modification exert a high discharge capacity of 276.5 mAh g -1 at 30 °C without external pressure, delivering a retention of 81.7% after 100 cycles at 25 mA g -1 during 2.0-4.7 V. This work provides a guideline for developing high-voltage solid-state lithium metal batteries via interfacial design.

Hu, Xinchao [Xiamen University (China)]↗
NASA NTRS1993

Hypersonic flow past open cavities

The hypersonic flow over a cavity is investigated. The time-dependent compressible Navier-Stokes equations, in terms of mass averaged variables, are numerically solved. An implicit algorithm, with a subiteration procedure to recover time-accuracy, is used to perform the time-accurate computations. The objective of the study is to investigate the effects of Reynolds number and cavity dimensions. The comparison of the computations with available experimental data, in terms of time mean static pressure, heat transfer, and Mach number show good agreement. In the computations large vortex structures, which adversely affect the cavity flow characteristics, are observed at the rear of the cavity. A self-sustained oscillatory motion occurs within the cavity over a range of Reynolds number and cavity dimensions. The frequency spectra of the oscillations show good agreement with a modified semi-empirical relation.

Morgenstern, Alagacyr, Jr.↗
NASA NTRS1994

Hypersonic flow past open cavities

The hypersonic flow over a cavity is investigated. The time-dependent compressible Navier-Stokes equations are numerically solved. An implicit algorithm, with a subiteration procedure to recover time accuracy, is used to perform the time-accurate computations. The objective of the study is to investigate the effects of Reynolds number and cavity dimensions. The comparsion of the computations with available experimental data, in terms of time mean static pressure, heat transfer, and Mach number, show good agreement. In the computations large vortex structures, which adversely affect the cavity flow characteristics, are observed at the rear of the cavity. A self-sustained oscillatory motion occurs within the cavity over a range of Reynolds number and cavity dimensions. The frequency spectra of the oscillations show good agreement with a modified semiempirical relation.

Morgenstern, Algacyr, Jr.↗
NASA NTRS2005

Single-Chip FPGA Azimuth Pre-Filter for SAR

A field-programmable gate array (FPGA) on a single lightweight, low-power integrated-circuit chip has been developed to implement an azimuth pre-filter (AzPF) for a synthetic-aperture radar (SAR) system. The AzPF is needed to enable more efficient use of data-transmission and data-processing resources: In broad terms, the AzPF reduces the volume of SAR data by effectively reducing the azimuth resolution, without loss of range resolution, during times when end users are willing to accept lower azimuth resolution as the price of rapid access to SAR imagery. The data-reduction factor is selectable at a decimation factor, M, of 2, 4, 8, 16, or 32 so that users can trade resolution against processing and transmission delays. In principle, azimuth filtering could be performed in the frequency domain by use of fast-Fourier-transform processors. However, in the AzPF, azimuth filtering is performed in the time domain by use of finite-impulse-response filters. The reason for choosing the time-domain approach over the frequency-domain approach is that the time-domain approach demands less memory and a lower memory-access rate. The AzPF operates on the raw digitized SAR data. The AzPF includes a digital in-phase/quadrature (I/Q) demodulator. In general, an I/Q demodulator effects a complex down-conversion of its input signal followed by low-pass filtering, which eliminates undesired sidebands. In the AzPF case, the I/Q demodulator takes offset video range echo data to the complex baseband domain, ensuring preservation of signal phase through the azimuth pre-filtering process. In general, in an SAR I/Q demodulator, the intermediate frequency (fI) is chosen to be a quarter of the range-sampling frequency and the pulse-repetition frequency (fPR) is chosen to be a multiple of fI. The AzPF also includes a polyphase spatial-domain pre-filter comprising four weighted integrate-and-dump filters with programmable decimation factors and overlapping phases. To prevent aliasing of signals, the bandwidth of the AzPF is made 80 percent of fPR/M. The choice of four as the number of overlapping phases is justified by prior research in which it was shown that a filter of length 4M can effect an acceptable transfer function. The figure depicts prototype hardware comprising the AzPF and ancillary electronic circuits. The hardware was found to satisfy performance requirements in real-time tests at a sampling rate of 100 MHz.

Gudim, Mimi↗
NASA NTRS2005

Effect of Tube Geometry on Regenerative Cooling Performance

The flowfield characteristics in a rocket engine coolant channels are analyzed by use of a commercial CFD and multiphysics software developed by the CFD Research Corp. called CFD-ACE+. The channels are characterized by high Reynolds number flow, varying aspect ratio, varying curvature, asymmetric and symmetric heating. The supercritical hydrogen coolant introduces large property variations that have a strong influence on the developing flow and the resulting heat transfer. This paper only shows the effect of aspect ratio and curvature for constant properties.

Parris, Daniel K.↗
NASA NTRS2011

Assessment of CFD Hypersonic Turbulent Heating Rates for Space Shuttle Orbiter

Turbulent CFD codes are assessed for the prediction of convective heat transfer rates at turbulent, hypersonic conditions. Algebraic turbulence models are used within the DPLR and LAURA CFD codes. The benchmark heat transfer rates are derived from thermocouple measurements of the Space Shuttle orbiter Discovery windward tiles during the STS-119 and STS-128 entries. The thermocouples were located underneath the reaction-cured glass coating on the thermal protection tiles. Boundary layer transition flight experiments conducted during both of those entries promoted turbulent flow at unusually high Mach numbers, with the present analysis considering Mach 10{15. Similar prior comparisons of CFD predictions directly to the flight temperature measurements were unsatisfactory, showing diverging trends between prediction and measurement for Mach numbers greater than 11. In the prior work, surface temperatures and convective heat transfer rates had been assumed to be in radiative equilibrium. The present work employs a one-dimensional time-accurate conduction analysis to relate measured temperatures to surface heat transfer rates, removing heat soak lag from the flight data, in order to better assess the predictive accuracy of the numerical models. The turbulent CFD shows good agreement for turbulent fuselage flow up to Mach 13. But on the wing in the wake of the boundary layer trip, the inclusion of tile conduction effects does not explain the prior observed discrepancy in trends between simulation and experiment; the flight heat transfer measurements are roughly constant over Mach 11-15, versus an increasing trend with Mach number from the CFD.

Wood, William A.↗
NASA NTRS2004

Effects of Freestream Turbulence on Turbine Blade Heat Transfer

Experiments have shown that moderate turbulence levels can nearly double turbine blade stagnation region heat transfer. Data have also shown that heat transfer is strongly affected by the scale of turbulence as well as its level. In addition to the stagnation region, turbulence is often seen to increase pressure surface heat transfer. This is especially evident at low to moderate Reynolds numbers. Vane and rotor stagnation region, and vane pressure surface heat transfer augmentation is often seen in a pre-transition environment. Accurate predictions of transition and relaminarization are critical to accurately predicting blade surface heat transfer. An approach is described which incorporates the effects of both turbulence level and scale into a CFD analysis. The model is derived from experimental data for cylindrical and elliptical leadng edges. Results using this model are compared to experimental data for both vane and rotor geometries. The comparisons are made to illustrate that using a model which includes the effects of turbulence length scale improves agreement with data, and to illustrate where improvements in the modeling are needed.

Boyle, Robert J.↗
NASA NTRS1982

Jet array impingement flow distributions and heat transfer characteristics. Effects of initial crossflow and nonuniform array geometry

Two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate are considered. The jet flow, after impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the heat transfer surface. The configurations considered are intended to model those of interest in current and contemplated gas turbine airfoil midchord cooling applications. The effects of an initial crossflow which approaches the array through an upstream extension of the channel are considered. Flow distributions as well as heat transfer coefficients and adiabatic wall temperatures resolved to one streamwise hole spacing were measured as a function of the initial crossflow rate and temperature relative to the jet flow rate and temperature. Both Nusselt number profiles and dimensionless adiabatic wall temperature (effectiveness) profiles are presented and discussed. Special test results which show a significant reduction of jet orifice discharge coefficients owing to the effect of a confined crossflow are also presented, along with a flow distribution model which incorporates those effects. A nonuniform array flow distribution model is developed and validated.

Florschuetz, L. W.↗
NASA NTRS1985

Analysis of buoyancy effect on fully developed laminar heat transfer in a rotating tube

Laminar heat transfer is analyzed in a tube rotating about an axis perpendicular to the tube axis. The solution applies for flow that is either radially outward from the axis of rotation, or radially inward toward the axis of rotation. The conditions are fully developed, and there is uniform heat addition at the tube wall. The analysis is performed by expanding velocities and temperature in power series using the Taylor number as a perturbation parameter. Coriolis and buoyancy forces caused by tube rotation are included, and the solution is calculated through second-order terms. The secondary flow induced by the Coriolis terms always tends to increase the heat transfer coefficient; this effect can dominate for small wall heating. For radial inflow, buoyancy also tends to improve heat transfer. For radial outflow, however, buoyancy tends to reduce heat transfer; for large wall heating this effect can dominate, and there is a net reduction in heat transfer coefficient.

Siegel, R.↗
NASA NTRS1961

Effects of Cone Angle, Mach Number, and Nose Blunting on Transition at Supersonic Speeds

An investigation has been made to determine the transition characteristics of a group of blunt cones which varied in included apex angle from 27 deg to 60 deg over a Mach number range from 1.61 to 2.20 and a range of tunnel Reynolds number per foot from about 1.5 x 10(exp 6) to 8.0 x 10(exp 6). The tests were made at zero angle of attack and with zero heat transfer. The results indicate that the general level of transition Reynolds number based on boundary-layer momentum thickness and local flow conditions just outside the boundary layer varied between 600 and 1,100. Changes in Mach number had little effect on transition distance and transition Reynolds number for the near-sharp or very small bluntnesses. The effect of Mach number variation on the larger hemispherical bluntnesses was much stronger, with the strongest Mach number effect occurring for Mach numbers between 1.61 and 1.82. With an increase in nose radius, there was a strong decrease in transition distance and transition Reynolds number at the lower Mach numbers. This adverse effect tended to become weaker with increase in Mach number. An increase in cone angle at a constant Mach number caused a reduction in transition distance and transition Reynolds number for the blunt configurations which had approximately the same values of nose radius.

Czarnecki, K. R.↗