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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Hydrogenolysis of n -eicosane over Ru-based catalysts in a continuous flow reactor

The hydrogenolysis of n-eicosane (C 20 H 42 ) was studied under differential conditions over Ru-based catalysts including Ru/SiO 2 , Ru/TiO 2 , and Ru/SBA-15, using a continuous flow reactor that was specially designed for large hydrocarbon reactants that are solids at room temperature. Similar rates and product distributions were obtained for Ru/SiO 2 and Ru/SBA-15 at 433 K, with the most abundant products being C 1 and C 19 hydrocarbons and smaller amounts of C 8 to C 18 also being produced. The higher yield of C 1 and C 19 indicates that cleavage of the terminal C-C bond is somewhat more facile than an internal C-C bond. At 473 K the product distribution shifted to mostly C 1 suggesting that, at this temperature, the adsorbed alkyl fragments undergo complete C-C bond scission prior to desorbing. Here, the conversion was also found to be inversely proportional to the H 2 pressure. Similar results were obtained for Ru/TiO 2 except this catalyst was found to be less active than both Ru/SiO 2 and Ru/SBA-15.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Preconditioners for multiphase poromechanics with strong capillarity

This paper aims to enhance the performance of Newton–Krylov solvers for coupled poromechanical problems with two-phase flow. In particular, we investigate the impact of capillary pressure on preconditioning strategies. Capillarity complicates the coupling between the solid deformation and fluid pressure degrees of freedom, as well as increases the nonlinearity of the system. Depending on the capillary pressure relation used in the constitutive formulation, the flow equations may exhibit a spectrum of advection-dominated to diffusion-dominated behavior. We propose preconditioning approaches that account for this behavior and lead to robust numerical performance within a broad range of regimes.

42 ENGINEERING↗
NASA NTRS2010

Progress on a Rayleigh Scattering Mass Flux Measurement Technique

A Rayleigh scattering diagnostic has been developed to provide mass flux measurements in wind tunnel flows. Spectroscopic molecular Rayleigh scattering is an established flow diagnostic tool that has the ability to provide simultaneous density and velocity measurements in gaseous flows. Rayleigh scattered light from a focused 10 Watt continuous-wave laser beam is collected and fiber-optically transmitted to a solid Fabry-Perot etalon for spectral analysis. The circular interference pattern that contains the spectral information that is needed to determine the flow properties is imaged onto a CCD detector. Baseline measurements of density and velocity in the test section of the 15 cm x 15 cm Supersonic Wind Tunnel at NASA Glenn Research Center are presented as well as velocity measurements within a supersonic combustion ramjet engine isolator model installed in the tunnel test section.

Mielke-Fagan, Amy F.↗
NASA NTRS1995

SRM Internal Flow Tests and Computational Fluid Dynamic Analysis: Titan, ASRM, and Subscale Motor Analyses - Volume 3

A computational fluid dynamics (CFD) analysis has been performed on the aft slot region of the Titan 4 Solid Rocket Motor Upgrade (SRMU). This analysis was performed in conjunction with MSFC structural modeling of the propellant grain to determine if the flow field induced stresses would adversely alter the propellant geometry to the extent of causing motor failure. The results of the coupled CFD/stress analysis have shown that there is a continual increase of flow field resistance at the aft slot due to the aft segment propellant grain being progressively moved radially toward the centerline of the motor port. This 'bootstrapping' effect between grain radial movement and internal flow resistance is conducive to causing a rapid motor failure.

Source record↗
NASA NTRS1974

Liquefaction dynamics of n-octadecane in cylindrical coordinates

The study presents one method of mathematically modeling the effects of gravity-induced free convection upon the melting phenomena of a finite paraffin slab. The theoretical model is based on the numerical computer solution of the solid phase and liquid phase energy equations, coupled with an imposed ideal-viscous flow approximation. An implicit alternating-direction technique is used as the finite-difference approximation for the basic energy equations in the numerical solution. The theoretical predictions are compared to experimental data from an annular test cell, in which n-octadecane, C18H38, was used as the test material. The results show that the model is a good first approximation to the solution of solid-liquid phase change involving gravity-induced free convection.

Bain, R. L.↗
NASA NTRS2014

Development of Naphthalene PLIF for Visualizing Ablation Products From a Space Capsule Heat Shield

The Orion Multi-Purpose Crew Vehicle (MPCV) will use an ablative heat shield. To better design this heat shield and others that will undergo planetary entry, an improved understanding of the ablation process would be beneficial. Here, a technique developed at The University of Texas at Austin that uses planar laser-induced fluorescence (PLIF) of a low-temperature sublimating ablator (naphthalene) to enable visualization of the ablation products in a hypersonic flow is applied. Although high-temperature ablation is difficult and expensive to recreate in a laboratory environment, low-temperature sublimation creates a limited physics problem that can be used to explore ablation-product transport in a hypersonic flow-field. In the current work, a subscale capsule reentry vehicle model with a solid naphthalene heat shield has been tested in a Mach 5 wind tunnel. The PLIF technique provides images of the spatial distribution of sublimated naphthalene in the heat-shield boundary layer, separated shear layer, and backshell recirculation region. Visualizations of the capsule shear layer using both naphthalene PLIF and Schlieren imaging compared favorably. PLIF images have shown high concentrations of naphthalene in the capsule separated flow region, intermittent turbulent structures on the heat shield surface, and interesting details of the capsule shear layer structure. It was shown that, in general, the capsule shear layer appears to be more unsteady at lower angels of attack. The PLIF images demonstrated that during a wind tunnel run, as the model heated up, the rate of naphthalene ablation increased, since the PLIF signal increased steadily over the course of a run. Additionally, the shear layer became increasingly unsteady over the course of a wind tunnel run, likely because of increased surface roughness but also possibly because of the increased blowing. Regions with a relatively low concentration of naphthalene were also identified in the capsule backshell recirculation region and are most likely the result of cross-flow-induced vortices on the capsule afterbody.

Combs, C. S.↗
NASA NTRS1980

Numerical simulation of three-dimensional boattail afterbody flow fields

The thin shear layer approximations of the three-dimensional, compressible Navier-Stokes equations are solved for subsonic, transonic, and supersonic flow over axisymmetric boattail bodies at moderate angles of attack. The plume is modeled by a solid body configuration identical to those used in experimental tests. An implicit algorithm of second-order accuracy is used to solve the equations on the ILLIAC IV computer. The turbulence is expressed by an algebraic model applicable to three-dimensional flow fields with moderate separation. The computed results compare favorably with three different sets of experimental data reported by Reubush, Shrewsbury, and Benek, respectively

Deiwert, G. S.↗
NASA NTRS1981

Dynamics of solid dispersions in oil during the lubrication of point of contacts. Part 2: Molybdenum disulfide

A Hertzian contact consisting of a steel ball in contact with a glass disk is lubricated with MoS2 dispersions and observed by optical microscopy at various slide/roll conditions. In general the behavior of MoS2 and graphite are similar. That is, the solids tend to enter the contact and form a film on the contacting surfaces whenever a rolling component of motion is used, but solid particles seldom enter the contact during pure sliding. The MoS2 has more pronounced plastic flow behavior than graphite. However, the polished steel ball is more readily scratched by MoS2 than by graphite. Under the conditions of these studies, lower friction and wear are observed with pure oil rather than with the dispersions. However under other conditions (such as different contact geometry or rougher surfaces) the solid lubricant dispersions might be beneficial.

Cusano, C.↗
DOE OSTI2023

Operational and scaling-up barriers of SOEC and mitigation strategies to boost H 2 production- a comprehensive review

Solid oxide electrolysis cells (SOECs) proffer a flexible and environmentally friendly solution to reduce CO 2 emissions and/or produce H 2 fuel for various applications. Here, the integration of this technology with renewable energy systems makes them even more promising in realizing a near-perpetual green energy infrastructure in the near future. SOEC technology has achieved stupendous improvement in recent years, and some of the limiting factors to the commercialization of this technology have been explored. It is, therefore, necessary to have a succinct outlook of the different factors that contribute to the recent developments in SOEC technology. The current work presents a comprehensive review of the state-of-the-art SOEC component materials and their degradation mechanisms, SOEC modeling essentials and efficiencies, and the scalability of SOECs. Although SOEC is considered a highly promising technology and sufficient multifaceted research has been done, yet not been widely commercialized. Despite the improvement to mitigate degradation of the SOEC materials, a large share of the degradation concerns sprang from charge transfer reaction at the triple-phase boundaries of the H 2 -electrode. Part of which can be improved by microkinetic modeling of these materials supported by their characterization to give insight into their development. Some other directions for the future in advancing this technology toward the commercialization stage are thoroughly addressed.

08 HYDROGEN↗
NASA NTRS1999

Investigation of Diffusion Flame Tip Thermodiffusive and Hydrodynamic Instability under Microgravity Conditions

We employ the opposed flow flame-spread configuration in order to examine flame-front instability of diffusion flames near cold, solid boundaries. The thermo-diffusive and hydrodynamic instabilities can transform an initially planar flame front into an irregularly curved, corrugated, possibly fragmented front. Under ordinary 1-g conditions, the buoyancy-induced flow masks the thermo-diffusive and hydrodynamic instabilities and produces planar flames. Such stable spreading flames have been observed for decades in laboratory experiments. Experiments in zero gravity are necessary to produce unstable flame fronts. The thermo-diffusive/hydrodynamic microgravity instability appears in diffusion flames such as, for example: the candle flame oscillations observed by Dietrich et al.; smolder instabilities on a recent Space Shuttle flight. Drs. T. Kashiwagi and S. Olson have attributed the latter to a lowered oxygen transport rate to the hot, reactive surface. Consider a burning surface near the flame extinction limit. The flow, or stretch, induced by the diffusion flame is weak, hence buoyancy plays a small role, thereby enabling previously secondary mechanisms, such as differential thermo-diffusion, to become the most important mechanisms. The flame leading edge becomes unstable; and diffusion flame breakup, oscillation, and rejoining all occur at a measurable frequency of approximately O(1 Hz). This project has only begun in January of this year, 1999. To date, there have been no flight experiments on flame spread instabilities. However, we have made numerous experiments in the NASA 2.2 and 5 second drop towers on flame spread over very thin cellulosic fuels. We have been very fortunate through a combination of factors, to be explained, to obtain some interesting, perhaps even compelling, results on diffusion flame instability in the presence of heat losses to cold surfaces.

Wichman, I. S.↗
NASA NTRS1973

Logic-controlled solid state switchgear for 270 volts dc

A feasibility study to design and demonstrate solid state switchgear in the form of circuit breakers and a power transfer switch is described. The switchgear operates on a nominal 270 V dc circuit and controls power to a load of up to 15 amperes. One circuit breaker may be interconnected to a second breaker to form a power transfer switch. On-off and transfer functions of the breakers or the transfer switch are remotely controlled. A number of reclosures with variable time delay between tripout and reclosure are programmed and controlled by integrated analog and COSMOS logic circuits. A unique commutation circuit, that generates only minimal transient disturbance to either source or load, was developed to interrupt current flow through the main SCR switching element. Laboratory tests demonstrated performance of the solid state circuit breakers over specified voltage and temperature ranges.

Sundberg, G. R.↗
NASA NTRS1987

Investigation of turbulent flow in highly curved ducts with application to turbomachinery components

Numerical predictions were performed using a semi-elliptic calculation procedure for the case of turbulent flow in passage through a 90 deg bend of square cross section. Two versions of the isotropic turbulent viscosity two equation k-epsilon model were used. The first, the wall function model (WFM), employs the logarithmic law-of-the-wall relation and the notion of equilibrium flow to set all the necessary boundary conditions at the first grid point adjacent to a solid wall. The second model, the Van Driest model (VDM), employs Prandtl's original mixing length formulation, in conjunction with Van Driest's semi-empirical relation for the mixing length, to calculate the turbulent viscosity in the near wall regions of the flow. In this case, boundary conditions for k and epsilon, required to calculate these quantities in the core of the flow, are obtained by matching the mixing length and Reynolds number model formulations in an overlapping region of the flow near the walls. In both cases the results obtained show an improvement over earlier calculations using an elliptic numerical procedure. This is attributed to the finer grids possible in the present work. Of the two models, the VDM formulation shows better overall conformity with the mean flow measurements. Neither model reproduces well the details of the stress distribution as a result of the implied isotropic turbulent viscosity.

Humphrey, J. A. C.↗
NASA NTRS1999

Study of Magnetic Damping Effect on Convection and Solidification Under G-Jitter Conditions

As shown by NASA resources dedicated to measuring residual gravity (SAMS and OARE systems), g-jitter is a critical issue affecting space experiments on solidification processing of materials. This study aims to provide, through extensive numerical simulations and ground based experiments, an assessment of the use of magnetic fields in combination with microgravity to reduce the g-jitter induced convective flows in space processing systems. We have so far completed asymptotic analyses based on the analytical solutions for g-jitter driven flow and magnetic field damping effects for a simple one-dimensional parallel plate configuration, and developed both 2-D and 3-D numerical models for g-jitter driven flows in simple solidification systems with and without presence of an applied magnetic field. Numerical models have been checked with the analytical solutions and have been applied to simulate the convective flows and mass transfer using both synthetic g-jitter functions and the g-jitter data taken from space flight. Some useful findings have been obtained from the analyses and the modeling results. Some key points may be summarized as follows: (1) the amplitude of the oscillating velocity decreases at a rate inversely proportional to the g-jitter frequency and with an increase in the applied magnetic field; (2) the induced flow approximately oscillates at the same frequency as the affecting g-jitter, but out of a phase angle; (3) the phase angle is a complicated function of geometry, applied magnetic field, temperature gradient and frequency; (4) g-jitter driven flows exhibit a complex fluid flow pattern evolving in time; (5) the damping effect is more effective for low frequency flows; and (6) the applied magnetic field helps to reduce the variation of solutal distribution along the solid-liquid interface. Work in progress includes numerical simulations and ground-based measurements. Both 2-D and 3-D numerical simulations are being continued to obtain further information on g-jitter driven flows and magnetic field effects. A physical model for ground-based measurements is completed and some measurements of the oscillating convection are being taken on the physical model. The comparison of the measurements with numerical simulations is in progress. Additional work planned in the project will also involve extending the 2-D numerical model to include the solidification phenomena with the presence of both g-jitter and magnetic fields.

Li, Ben Q.↗
DOE OSTI2023

Material flow behavior and microstructural refinement of AA6061 alloy during friction extrusion

In this work we used friction extrusion (FE), a solid phase processing technique, to produce dense, fully consolidated 5?mm rods of aluminum alloy 6061 (AA6061). The combination of large shear stresses and high temperatures at the tool-billet interface during extrusion produced equiaxed, dynamically recrystallized grains and finely distributed precipitates. Texture and microstructure evolution during extrusion was investigated in detail using scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. Smoothed particle hydrodynamics simulation was performed to study complex material flow during extrusion. Simulation results suggest spiral material flow during extrusion which corroborated experimental results. Advantages of friction extruded microstructure over conventionally extruded counterparts are also explored using flash annealing for solution treatment followed by artificial aging. Mechanical properties of the as-friction extruded, and the artificially aged specimens were evaluated using tensile testing and compared with conventional extruded material properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2019

Observations of Surface Mass Balance on Pine Island Glacier, West Antarctica, and the Effect of Strain History in Fast-Flowing Sections

Surface mass balance (SMB) is the net input of mass on a glacier's upper surface, composed of snow deposition, melt and erosion processes, and is a major contributor to the overall mass balance. Pine Island Glacier (PIG) in West Antarctica has been dynamically imbalanced since the early 1990s, indicating that discharge of solid ice into the oceans exceeds snow deposition. However, observations of the SMB pattern on the fast flowing regions are scarce, and are potentially affected by the firn's strain history. Here, we present new observations from radar-derived stratigraphy and a relatively dense network of firn cores, collected along a ~900 km traverse of PIG. Between 1986 and 2014, the SMB along the traverse was 0.505 m w.e. a−1 on average with a gradient of higher snow deposition in the South-West compared with the North-East of the catchment. We show that along ~80% of the traverse the strain history amounts to a misestimation of SMB below the nominal uncertainty, but can exceed it by a factor 5 in places, making it a significant correction to the SMB estimate locally. We find that the strain correction changes the basin-wide SMB by ~0.7 Gt a−1 and thus forms a negligible (1%) correction to the glacier's total SMB.

ice core↗
NASA NTRS2007

Tandem Cylinder Noise Predictions

In an effort to better understand landing-gear noise sources, we have been examining a simplified configuration that still maintains some of the salient features of landing-gear flow fields. In particular, tandem cylinders have been studied because they model a variety of component level interactions. The present effort is directed at the case of two identical cylinders spatially separated in the streamwise direction by 3.7 diameters. Experimental measurements from the Basic Aerodynamic Research Tunnel (BART) and Quiet Flow Facility (QFF) at NASA Langley Research Center (LaRC) have provided steady surface pressures, detailed off-surface measurements of the flow field using Particle Image Velocimetry (PIV), hot-wire measurements in the wake of the rear cylinder, unsteady surface pressure data, and the radiated noise. The experiments were conducted at a Reynolds number of 166 105 based on the cylinder diameter. A trip was used on the upstream cylinder to insure a fully turbulent shedding process and simulate the effects of a high Reynolds number flow. The parallel computational effort uses the three-dimensional Navier-Stokes solver CFL3D with a hybrid, zonal turbulence model that turns off the turbulence production term everywhere except in a narrow ring surrounding solid surfaces. The current calculations further explore the influence of the grid resolution and spanwise extent on the flow and associated radiated noise. Extensive comparisons with the experimental data are used to assess the ability of the computations to simulate the details of the flow. The results show that the pressure fluctuations on the upstream cylinder, caused by vortex shedding, are smaller than those generated on the downstream cylinder by wake interaction. Consequently, the downstream cylinder dominates the noise radiation, producing an overall directivity pattern that is similar to that of an isolated cylinder. Only calculations based on the full length of the model span were able to capture the complete decay in the spanwise correlation, thereby producing reasonable noise radiation levels.

Lockard, David P.↗
NASA NTRS2006

Comprehensive Report of Fan Performance From Duct Rake Instrumentation on 1.294 Pressure Ratio, 806 ft/sec Tip Speed Turbofan Simulator Models

A large scale model representative of an advanced ducted propulsor-type, low-noise, very high bypass ratio turbofan engine was tested for acoustics, aerodynamic performance, and off-design operability in the NASA Glenn 9- by 15-Foot Low-Speed Wind Tunnel. The test was part of NASA s Advanced Subsonic Technology Noise Reduction Program. The low tip speed fan, nacelle, and un-powered core passage were simulated. As might be expected, the effect of stall management casing treatment was a performance penalty. Reducing the recirculating flow at the fan tip reduced the penalty while still providing sufficient stall margin. Two fans were tested with the same aerodynamic design; one with graphite composite material, and the other with solid titanium. There were surprising performance differences between the two fans, though both blades showed some indication of transitional flow near the tips. Though the pressure and temperature ratios were low for this fan design, the techniques used to improve thermocouple measurement accuracy gave repeatable data with adiabatic efficiencies agreeing within 1 percent. The measured fan adiabatic efficiency at simulated takeoff conditions was 93.7 percent and matched the design intent.

Jeracki, Robert J.↗
NASA NTRS2016

Correlation of Normal Gravity Mixed Convection Blowoff Limits with Microgravity Forced Flow Blowoff Limits

The axisymmetric rod geometry in upward axial stagnation flow provides a simple way to measure normal gravity blowoff limits to compare with microgravity Burning and Suppression of Solids - II (BASS-II) results recently obtained aboard the International Space Station. This testing utilized the same BASS-II concurrent rod geometry, but with the addition of normal gravity buoyant flow. Cast polymethylmethacrylate (PMMA) rods of diameters ranging from 0.635 cm to 3.81 cm were burned at oxygen concentrations ranging from 14 to 18% by volume. The forced flow velocity where blowoff occurred was determined for each rod size and oxygen concentration. These blowoff limits compare favorably with the BASS-II results when the buoyant stretch is included and the flow is corrected by considering the blockage factor of the fuel. From these results, the normal gravity blowoff boundary for this axisymmetric rod geometry is determined to be linear, with oxygen concentration directly proportional to flow speed. We describe a new normal gravity 'upward flame spread test' method which extrapolates the linear blowoff boundary to the zero stretch limit in order to resolve microgravity flammability limits-something current methods cannot do. This new test method can improve spacecraft fire safety for future exploration missions by providing a tractable way to obtain good estimates of material flammability in low gravity.

microgravity↗