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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Rapid flow fractionation of particles combining liquid and particulate dielectrophoresis

Rapid, size-based, deposition of particles from liquid suspension is accomplished using a nonuniform electric field created by coplanar microelectrode strips patterned on an insulating substrate. The scheme uses the dielectrophoretic force both to distribute aqueous liquid containing particles and, simultaneously, to separate the particles. Size-based separation is found within nanoliter droplets formed along the structure after voltage removal. Bioparticles or macromolecules of similar size can also be separated based on subtle differences in dielectric property, by controlling the frequency of the AC current supplied to the electrodes.

King, Michael R.↗
NASA NTRSDate not supplied

Going With the Flow: Using a Particle Dispersion Model to Reveal Links Between Ocean Ecosystems and Marine Aerosols

Marine biogenic particle contributions to atmospheric aerosol concentrations are not well understood though they are important for determining cloud optical and cloud nucleating properties. Here we examine the relationship between marine aerosol measurements with satellite and model fields of ocean biology and meteorological variables during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES). NAAMES consisted of four field campaigns between November 2015 and April 2018 that aligned with the four major phases of the annual phytoplankton bloom cycle. The FLEXPART Lagrangian particle dispersion model is used to connect these variables spatiotemporally to ship-based aerosol. We find that correlations between some aerosol measurements with satellite measured and modelled variables increase with increasing trajectory length. This indicates biological and meteorological processes over the air mass history are influential to measured particle properties. For example, results show organic aerosol mass is driven by biogenic volatile organic compound (VOC) emissions from photosynthesis by phytoplankton stocks during advection into the region. In contrast, primary marine aerosol (PMA) concentrations showed better correlations to variables weighted with shorter air mass residence times, which reflects their localized origin as primary emissions. Evidence also suggest variability in PMA concentrations likely play an important role in VOC emission removal. The removal of VOCs lessen their impact on particle number and mass concentrations. The sensitivity of marine aerosols to the main ecosystem-atmosphere drivers and its dependence on air mass history are to be further discussed.

Kevin J Sanchez↗
NASA NTRS1977

Nonlinear Alfven waves in high-speed solar wind streams

A nonlinear proton distribution function that is an exact stationary solution of the nonlinear Vlasov equation and Maxwell's equations and which supports a single nonlinear transverse Alfven (ion cyclotron) wave that is circularly polarized and nondispersive is proposed for most of the observations during high-speed solar wind streams. This nonlinear distribution removes the strong Alfven wave instability, inconsistent with the persistence of the observed proton distribution functions in high-speed streams, found by the linear stability analysis. Model temperature anisotropies and drift velocities of the two spatially inhomogeneous bi-Maxwellian components are consistent with typical proton velocity distributions measured in high-speed streams at 1 AU. Two derived relations for each of the wave number and the phase velocity of the wave are obeyed within experimental uncertainties by two typical proton measurements. Our model also predicts that the alpha particle bulk flow velocity exceeds the proton particle bulk flow velocity, as is observed.

Abraham-Shrauner, B.↗
NASA NTRS1986

Cloud particle effects on laminar flow in the NASA LEFT program - Preliminary results

Laminar flow offers the promise of significant fuel savings on future commercial transport aircraft, but laminar flow can be lost while encountering clouds or haze at cruise conditions. To quantify the effect of cloud particles on laminar flow during typical airline operating conditions, and evaluate candidate cloud particle detection instrument concepts for future laminar flow aircraft, two types of cloud particle detectors are being flown aboard a NASA JetStar aircraft in the Leading Edge Flight Test (LEFT) program. The instrumentation is described, and preliminary results and conclusions are presented.

Davis, R. E.↗
NASA NTRS1993

Flow instability in particle-bed nuclear reactors

The particle-bed core offers mitigation of some of the problems of solid-core nuclear rocket reactors. Dividing the fuel elements into small spherical particles contained in a cylindrical bed through which the propellant flows radially, may reduce the thermal stress in the fuel elements, allowing higher propellant temperatures to be reached. The high temperature regions of the reactor are confined to the interior of cylindrical fuel assemblies, so most of the reactor can be relatively cool. This enables the use of structural and moderating materials which reduce the minimum critical size and mass of the reactor. One of the unresolved questions about this concept is whether the flow through the particle-bed will be well behaved, or will be subject to destructive flow instabilities. Most of the recent analyses of the stability of the particle-bed reactor have been extensions of the approach of Bussard and Delauer, where the bed is essentially treated as an array of parallel passages, so that the mass flow is continuous from inlet to outlet through any one passage. A more general three dimensional model of the bed is adopted, in which the fluid has mobility in three dimensions. Comparison of results of the earlier approach to the present one shows that the former does not accurately represent the stability at low Re. The more complete model presented should be capable of meeting this deficiency while accurately representing the effects of the cold and hot frits, and of heat conduction and radiation in the particle-bed. It can be extended to apply to the cylindrical geometry of particle-bed reactors without difficulty. From the exemplary calculations which were carried out, it can be concluded that a particle-bed without a cold frit would be subject to instability if operated at the high temperatures desired for nuclear rockets, and at power densities below about 4 megawatts per liter. Since the desired power density is about 40 megawatts per liter, it can be concluded that operation at design exit temperature but at reduced power could be hazardous for such a reactor. But the calculations also show that an appropriate cold frit could very likely cure the instability. More definite conclusions must await calculations for specific designs.

Kerrebrock, Jack L.↗
NASA NTRS1992

Simulation of particle mixing by turbulent convective flows on the connection machine

Mixing of particles by chaotic flow fields was simulated on the Connection Machine. Each cell was assigned to the processor, and the coordinates of particles residing on the cell were kept in the local memory of the processor. This approach implies the exchange between the local memories, when a particle moves from one cell to another. Approximately 10 exp 5 particles were injected into a time-dependent flow field obtained by solving the nonlinear system of partial differential equations describing turbulent thermal convection. The flow field was calculated on a CRAY, and data were transferred to a CM-200 through a high-speed HIPPI channel.

Malevsky, A. V.↗
DOE OSTI2024

Direct numerical simulation of open-channel flow over a heterogeneous particle bed at low relative submergence

In this article, this study investigates turbulent open-channel flows over beds of irregularly arranged particles, using direct numerical simulations at a friction Reynolds number of Re T = 300⁠. Two distinct cases are examined: a polydisperse bed (P800) composed of multiple layers of randomly distributed spheres of varying sizes, and a monodisperse bed (M1015) formed by a random distribution of uniform sized spheres, with a bottommost single layer of varied-sized particles to introduce realistic randomness. Our investigation unveils a rich network of low- and high-speed streaks within the flow field, exhibiting distinctive behaviors in different bed configurations. The P800 case presents a poorly organized flow pattern induced by the varied particle sizes and arrangements, while the M1015 case shows a more regular flow pattern, marked by larger streaks. We also observe that total wall shear stress is substantially influenced by surface roughness-induced drag, extending beyond the effects documented in existing studies of open-channel flows. The present study reveals intricate secondary flow patterns over irregular particle beds. Large-scale circulations are discerned around particle crests in the P800 case and localized circulations with increased turbulence in the M1015 case. Furthermore, analysis of Reynolds stress tensor components indicates that roughness disrupts coherent turbulent eddies, consequently mitigating peak stress. We quantify correlations between drag force and local fluid velocity fluctuations. Notably, a larger deviation in drag is observed in the P800 case compared to M1015, accentuating the influence of particle size and distribution on fluid–particle interactions.

42 ENGINEERING↗
NASA NTRS1999

Application of PIV to the Measurement of High Speed Jet Flows

The Particle Image Velocimetry, PIV, has been implemented for the investigation of high-speed jet flows at the NASA Langley Research Center. In this approach the velocity (displacement) is found as the location of a peak in the correlation map of particle images acquired in quick succession. In the study, the technique for the correct seeding of the flow field were developed and implemented and the operational parameters influencing the accuracy of the measurement have been optimized.

Lourenco, L.↗
DOE OSTI2024

An improved stochastic weighted particle method for boundary driven flows

Here, the stochastic weighted particle method (SWPM) is a generalization of the Direct Simulation Monte Carlo (DSMC) method where particle weights are variable and dynamic. SWPM is backed by a strong theoretical foundation but has not been critically evaluated for problems of practical interest. A thorough assessment of SWPM for boundary-driven flows reveals significant numerical artifacts near the boundary, notably a diverging heat flux. To correct the boundary heat flux, two modifications to SWPM are proposed: separated grouping and a spatially-dependent weight transfer function. To gauge the relative efficiency of SWPM in comparison to DSMC, a high-Mach-number wheel flow which forms a strong density gradient is also simulated.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1986

Calculation of confined gas-particle two-phase turbulent flows

Numerical calculations have been carried out for gas-particle confined turbulent flows using a recently developed two-phase turbulence closure model. The present modeling scheme utilizes Eulerian formulations of the transport equations and accounts for the combined effects of interphase slip and turbulent dispersion of particles. A multiple-scale turbulence model is used for the turbulent field modeling of the underlying fluid flow. For the particle size and particle loading considered in this study, the fluid turbulence transport equations must be modified to include the damping effects of particles. Predictions and comparisons are made in the fully developed gas-solid pipe flow and the confined particle-laden jet. Numerical results are in reasonably good agreement with the published experimental information.

Chen, C. P.↗
NASA NTRS1975

Drag coefficient equations for small particles in high speed flows

The paper determines the effect of various available drag coefficient equations on particle velocity calculations for typical two phase flows encountered in supersonic and turbulent laser velocimeter applications. The predictions of the particle drag coefficient equations are compared with experimental sphere drag data. For the laser velocimeter applications, the relative Mach number less than 2 and the relative Reynolds number less than 200 are of particular importance.

Walsh, M. J.↗
DOE OSTI2024

Debris-induced consequences on turbulence and vorticity in solar photovoltaic module-generated array wakes

Particle-laden flows in solar photovoltaic (PV) systems are inevitable, where wind-swept debris in open environments are carried by high winds and turbulence, coating panel surfaces or damaging structures. Particle deposition, or soiling, is a well-known issue for large-scale plants which rely on uninhibited solar rays for optimal production. But understanding the mechanisms leading to soiling requires a physical and fluid dynamics-centered focus, since turbulence dominates PV panel wakes and is also known to alter particle concentration and trajectories. This study presents an experimental campaign toward consequences of particle-laden flow between two model PV panels using time-resolved particle image velocimetry. The model array was subjected to varied particle volume fractions, including a tracer particle case and a water droplet case. Characterization of mean velocity, turbulence statistics, and mean kinetic energy within the single phase and, separately, particle phase flows showed modified features due to particle inertia. Images captured at a frequency of 1 kHz in the near wake of the upstream panel allow for a first experimental look at vorticity and convective velocity of vortex structures for single-phase and particle-phase flows which are crucial to debris transport and soiling in PV environments.

Energy & Fuels↗
NASA NTRS2015

Launch Environment Water Flow Simulations Using Smoothed Particle Hydrodynamics

This paper describes the use of Smoothed Particle Hydrodynamics (SPH) to simulate the water flow from the rainbird nozzle system used in the sound suppression system during pad abort and nominal launch. The simulations help determine if water from rainbird nozzles will impinge on the rocket nozzles and other sensitive ground support elements.

Smoothed Particle Hyrodynamics↗
DOE OSTI2024

Effects of particle size and AQDS on the flow of electron equivalents between magnetite and aqueous Fe2+

Magnetite can occur naturally in nano- to micro-size regimes and widely coexists with aqueous Fe2+ (Fe2+ (aq)) in natural environments. However, the effects of magnetite particle size on its interaction with Fe2+ (aq) in anoxic subsurface environments, particularly with redox-active organics, remain unclear. In this study, the interactions of Fe2+ (aq) with magnetite particles of 12 nm versus 109 nm (Mag-12 vs. Mag-109), with/without anthraquinone- 2,6-disulfonate (AQDS), were studied based on equilibrium Fe2+ (aq) concentrations, kinetics of AQDS reduction, and structural versus surface-localized Fe(II)/Fe(III) ratios (xstru and xsurf) of magnetite. In the absence of AQDS, Mag-12 tends to release Fe2+ (aq) at pH 7 but sorb Fe2+ (aq) at pH 8, while Fe2+ (aq) uptake by Mag-109 is observed at both pH 7 and 8. The amounts of Fe2+ (aq) adsorbed per unit area of Mag-109 is higher than that of Mag-12, due to the higher electron-accepting capacity of Mag-109 that facilitates interfacial electron transfer (IET) from surfaceassociated Fe(II) to structural Fe(III). The increases of xstru and xsurf in Mag-109 after reaction with Fe2+ (aq) at pH 7 and 8 suggest Fe2+ (aq) incorporation or electron injection into the structure of Mag-109. The presence of AQDS promotes Fe2+ (aq) uptake by both Mag-12 and Mag-109. However, AQDS reduction by Fe2+-amended Mag-12 results in the decrease of xstru and inhibits Fe2+ (aq) incorporation or electron injection into the structure. On the contrary, the increase of xstru observed in Fe2+-amended Mag-109 after reaction with AQDS suggests that Fe2+ (aq) incorporation or electron injection into the surface structure and then consequently into the interiors is more favorable for magnetite with larger particle sizes. The different flow directions of electron equivalents across the solid-solution interfaces can be attributed to the relatively higher electron-accepting capacity, i.e. redox potential, of Mag-109 than Mag-12; larger particle sizes facilitate IET from surface-associated Fe(II) to structural Fe(III) and promotes further Fe2+ (aq) uptake, culminating in the pronounced changes of redox potentials in magnetitebearing solutions. The results demonstrate that particle size and redox-active organics are important factors to affect reductive activity of Fe2+-magnetite system in redox-oscillating environments.

Peng, Huan↗
NASA NTRS1988

Performance of laser Doppler velocimeter with polydisperse seed particles in high speed flows

The flowfield behind an oblique shock wave, where the LDV measured velocities are seed particle size dependent, was used to investigate the effects of LDV system parameters on the range of detectable polydisperse seed particles. The parameters included frequency shifting, laser power, scattered signal amplification level, and number of required fringe crossings. The results showed that with polydisperse seed particles ranging from 0.1 to 4.0 microns available in the flow, the average diameter of the detected particles could change from 0.2 to 3.0 microns by changing different LDV system parameters. The effects of this shift in the range of detectable particles on the frequency response of LDV was discussed.

Samimy, M.↗
NASA NTRS2002

Particle Size Effects on Flow Properties of PS304 Plasma Spray Feedstock Powder Blend

The effects of BaF2-CaF2 particle size and size distribution on PS304 feedstock powder flowability have been investigated. Angular BaF2-CaF2 eutectic powders were produced by comminution and classified by screening to obtain 38 to 45 microns 45 to 106 microns, 63 to 106 microns, 45 to 53 microns, 63 to 75 microns, and 90 to 106 microns particle size distributions. The fluorides were added incrementally from 0 to 10 wt% to the other powder constituents of the PS304 feedstock: nichrome, chromia, and silver powders. The flow rate of the powder blends decreased linearly with increasing concentration of the fluorides. Flow was degraded with decreasing BaF2-CaF2 particle size and with increasing BaF2-CaF2 particle size distribution. A semiempirical relationship is offered to describe the PS304 powder blend flow behavior. The Hausner Ratio confirmed the funnel flow test results, but was slightly less sensitive to differences in BaF2-CaF2 particle size and size distribution. These findings may have applicability to other powders that do not flow easily, such as ceramic powders.

Stanford, Malcolm K.↗
NASA NTRS1983

Particle-sampling statistics in laser anemometers Sample-and-hold systems and saturable systems

The effect of the data-processing system on the particle statistics obtained with laser anemometry of flows containing suspended particles is examined. Attention is given to the sample and hold processor, a pseudo-analog device which retains the last measurement until a new measurement is made, followed by time-averaging of the data. The second system considered features a dead time, i.e., a saturable system with a significant reset time with storage in a data buffer. It is noted that the saturable system operates independent of the particle arrival rate. The probabilities of a particle arrival in a given time period are calculated for both processing systems. It is shown that the system outputs are dependent on the mean particle flow rate, the flow correlation time, and the flow statistics, indicating that the particle density affects both systems. The results are significant for instances of good correlation between the particle density and velocity, such as occurs near the edge of a jet.

Edwards, R. V.↗