Search NASA⌕ Search

SEARCH · Search NASA

Results for “lateral mixing”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Preparation and Characterization of Polyimide Nanocomposites

Many properties of polymeric materials can be enhanced by dispersing small quantities of clay nanocomposites throughout the polymer. Among the enhancements are increases in modulus and resistance to erosion by atomic oxygen and reductions in thermal expansivity, gas permeability, and flammability. To achieve the full extent of enhancement with these polymer-clay nanocomposites, the clay nanoparticles, which have thicknesses of only one-to-several nanometers and lengths and widths of hundreds of nanometers to micrometers, must be exfoliated one from another and then individually dispersed throughout the polymer. This dispersion is achieved only after alkali metal cations (usually Na(+)) that reside on the surfaces of the nanoparticles have been replaced by organocations (typically a quaternary amine cation). This renders the surface of the nanoparticle a more hospitable interface for the organic polymer matrix. Following the cation exchange, the organic clay is either mixed directly into the polymer or is dispersed in monomer which is later polymerized around the nanoparticle.

Orwoll, Robert A.↗
NASA NTRS1982

Programming real-time executives in higher order language

Methods by which real-time executive programs can be implemented in a higher order language are discussed, using HAL/S and Path Pascal languages as program examples. Techniques are presented by which noncyclic tasks can readily be incorporated into the executive system. Situations are shown where the executive system can fail to meet its task scheduling and yet be able to recover either by rephasing the clock or stacking the information for later processing. The concept of deadline processing is shown to enable more effective mixing of time and information synchronized systems.

Foudriat, E. C.↗
NASA NTRS1984

Lunar dark-haloed impact craters - Origin and implications for early mare volcanism

Spectral, thermal, radar, and photogeologic data were used to determine the composition and origin of lunar dark-haloed craters. Analyses of reflectance spectra (near-infrared) of dark-haloed craters on light plains indicate that in every instance these craters exposed mare basalts which had previously been covered by varying thicknesses of highlands debris. In the Schiller-Schickard region a relatively thick highlands unit was emplaced as a result of the Orientale impact event. The results of recent remote sensing photogeologic and lunar samples studies indicate that mare volcanism was a significant process during much of the pre-Imbrian epoch and may have been initiated as early as 4.2-4.3 Ga. The very early volcanic episodes contributed materials to the lunar surface which were later incorporated into the upper portion of the highlands crust by subsequent impact mixing. On the basis of the data it is concluded that current models of the extent and duration of mare volcanisms, as well as those involving the composition of thermal evolution of the lunar interior will have to be revised.

Bell, J. F.↗
NASA NTRS1993

CITE 3 meteorological highlights

Meteorological highlights from the third NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation (GTE/CITE 3) are presented. During August and September 1989, research flights were conducted from Wallops Island, Virginia, and Natal, Brazil, and included airborne sampling of air masses over adjacent regions of the Atlantic Ocean. Isentropic backward trajectory calculations, wind vector/streamline fields, rawinsonde data, and GOES and METEOSAT satellite imagery are utilized to examine the meteorological conditions for each flight and to determine the transport paths of the sampled air masses. Some aspects of the chemical signatures of the sampled air are also discussed. During the series of flights based at Wallops Island, Virginia, the flow into the experiment area was governed primarily by the position of the North Atlantic subtropical anticyclone. The large-scale tropospheric circulation switched from primarily a marine flow during flights 1-4, to a predominantly offshore mid-latitude continental flow during flights 5-10. During these later flights, the regional influences of large eastern U.S. cities along with vertical mixing by typical summertime convective activity strongly influenced the chemical characteristics of the sampled air. During the series of flights based at Natal, Brazil, the dominant synoptic feature was the South Atlantic subtropical anticyclone which generally transported air across the tropical Atlantic toward eastern Brazil. Pronounced subsidence and a well-defined trade wind inversion often characterized the lower and middle troposphere over the Natal region. Some high-altitude recirculation of air from South America was observed, as was cross-equatorial transport which had come from northern Africa. Biomass burning plumes were observed on segments of all of the flights, the source region being the central and southern savannah regions of Africa.

Shipham, Mark C.↗
NASA NTRS1960

A Study of the Combustion of Aluminum Borohydride in a Small Supersonic Wind Tunnel

The combustion of aluminum borohydride in the Mach 2 airstream of a 3.84- by 10-inch wind tunnel was studied by analyzing gas samples taken from the airstream. Gas mixture composition was determined with the aid of a vacuum apparatus and gas chromatograph. The overall combustion efficiency of the fuel was assumed to be good because the combustion efficiency of its hydrogen component was found to be high. The increase of the lateral surface area of the combustion region was dependent upon the degree of mixing of fuel and its combustion products with air. In the flame zone where there was insufficient oxygen for complete combustion, the metal components of the fuel appeared to burn preferentially to the hydrogen component.

Allen, Harrison, Jr.↗
NASA NTRS1992

High speed jet noise research at NASA Lewis

The source noise portion of the High Speed Research Program at NASA LeRC is focused on jet noise reduction. A number of jet noise reduction concepts are being investigated. These include two concepts, the Pratt & Whitney ejector suppressor nozzle and the General Electric (GE) 2D-CD mixer ejector nozzle, that rely on ejectors to entrain significant amounts of ambient air to mix with the engine exhaust to reduce the final exhaust velocity. Another concept, the GE 'Flade Nozzle' uses fan bypass air at takeoff to reduce the mixed exhaust velocity and to create a fluid shield around a mixer suppressor. Additional concepts are being investigated at Georgia Tech Research Institute and at NASA LeRC. These will be discussed in more detail in later figures. Analytical methods for jet noise prediction are also being developed. Efforts in this area include upgrades to the GE MGB jet mixing noise prediction procedure, evaluation of shock noise prediction procedures, and efforts to predict jet noise directly from the unsteady Navier-Stokes equation.

Krejsa, Eugene A.↗
NASA NTRS1986

Experiments and modeling of dilution jet flow fields

Experimental and analytical results of the mixing of single, double, and opposed rows of jets with an isothermal or variable-temperature main stream in a straight duct are presented. This study was performed to investigate flow and geometric variations typical of the complex, three-dimensional flow field in the dilution zone of gas-turbine-engine combustion chambers. The principal results, shown experimentally and analytically, were the following: (1) variations in orifice size and spacing can have a significant effect on the temperature profiles; (2) similar distributions can be obtained, independent of orifice diameter, if momentum-flux ratio and orifice spacing are coupled; (3) a first-order approximation of the mixing of jets with a variable-temperature main stream can be obtained by superimposing the main-stream and jets-in-an-isothermal-crossflow profiles; (4) the penetration of jets issuing mixing is slower and is asymmetric with respect to the jet centerplanes, which shift laterally with increasing downstream distance; (5) double rows of jets give temperature distributions similar to those from a single row of equally spaced, equal-area circular holes; (6) for opposed rows of jets, with the orifice centerlines in line, the optimum ratio of orifice spacing to duct height is one-half the optimum value for single-side injection at the same momentum-flux ratiol and (7) for opposed rows of jets, with the orifice centerlines staggered, the optimum ratio of orifice spacing to duct height is twice the optimum value for single-side injection at the same momentum-flux ratio.

Holdeman, James D.↗
NASA NTRS1956

Intensity, Scale, and Spectra of Turbulence in Mixing Region of Free Subsonic Jet

Report presents the results of the measurements of intensity of turbulence, the longitudinal and lateral correlation coefficients, and the spectra of turbulence in a 3.5-inch-diameter free jet measured with hot-wire anemometers at exit Mach numbers from 0.2 to 0.7 and Reynolds numbers from 192,000 to 725,000.

Laurence, James C↗
NASA NTRS2001

Working Toward Nanotube Composites

One of the most attractive applications of single-wall carbon nanotubes (SWNT) is found in the area of structural materials. Nanotubes have a unique combination of high strength, modulus, and elongation to failure, and therefore have potential to significantly enhance the mechanical properties of today's composites. This is especially attractive for the aerospace industry looking for any chance to save weight. This is why NASA has chosen to tackle this difficult application of SWNT. Nanotube properties differ significantly from that of conventional carbon fibers, and a whole new set of problems, including adhesion and dispersion in the adhesive polymer matrix, must be resolved in order to engineer superior composite materials. From recent work on a variety of applications it is obvious that the wide range of research in nanotubes will lead to advances in physics, chemistry, and engineering. However, the possibility of ultralightweight structures is what causes dreamers to really get excited. One of the important issues in composite engineering is aspect ratio of the fibers, since it affects load transfer in composites. Nanotube length was a gray area for years, since they are formed in bundles, making it impossible to monitor individual nanotube length. Even though bundles are observed to be tens and hundreds of microns long, they can be built of relatively short tubes weakly bound by Van der Waals forces. Nanotube length can be affected by subsequent purification and ultrasound processing, which has been necessary in order to disperse nanotubes and introduce them into a polymer matrix. Some calculations show that nanotubes with 10(exp 5) aspect ratio may be necessary to achieve good load transfer. We show here that nanotubes produced in our laser system are as much as tens of microns long and get cut into lengths of hundreds of nanometers during ultrasound processing. Nanotube length was measured by AFM on pristine nanotube specimens as well, as after sonication. In each case great care was taken to measure individual nanotubes, rather than bundles. Pristine nanotubes were collected on quartz substrates placed directly in the laser oven and exposed for 0.5 s. This results in an equal mix of bundles and individual nanotubes. Nanotube length measurements were limited practically by the lateral span of the AFM scanner, but nanotube length is certainly in excess of 20 micrometers.

Arepalli, Sivaram↗
NASA NTRSDate not supplied

Test Capabilities of the NASA Langley Direct Connect Supersonic Combustion Test Facility

In 1969 a combustion-heated direct-connect test facility was assembled at the NASA Langley Research Center and used to support NASA’s Hypersonic Research Engine program. Later, the facility was used to support NASA’s generic hypersonic program, assessing the mixing, ignition, flame holding, and combustion characteristics of ramjet and scramjet combustors. Over the years, the facility has been updated and modified to conduct increasingly complicated tests. Today, the facility is known as the Direct Connect Supersonic Combustion Test Facility (DCSCTF) and is part of the NASA Langley Scramjet Test Complex. Recently, the facility has been used by external customers to test fuel-cooled and uncooled, flight-like test articles. Tests have been conducted at nominal Mach 5 flight conditions for up to 15 minutes of continuous operation. The facility remains a viable and useful tool in the support of various Department of Defense projects.

Diego P Capriotti↗
NASA NTRS1985

Mars missions and bases - A recent look

This paper discusses some of the key options for Mars programs, missions, bases, elements, and systems. Program and mission options include Mars flyby, orbiting, and landing missions; they include near-term 'sortie' missions, and later, longer-duration Mars-base missions. Key program and mission parameters include the mix of manned/unmanned elements, the number and types of space vehicles used, types of science done, trajectory options and implications launch timing and schedules, etc. The key mission parameters strongly affect the nature, sizing, and quantity of earth-to-orbit (ETO) vehicles. On-orbit assembly of space vehicles (SVs) is also an important related consideration. The potential degree of utilization of the Space Station (SS) and other then-existing elements is a key question, and several possibilities are discussed in this paper. Several configurations of SVs are provided. Several options are identified for the Mars base infra-structure, and parametric data is shown for buildup of bases as a function of mission and vehicle type. Technologies required for the missions are also discussed.

Butler, J. M., Jr.↗
NASA NTRS1987

Analysis of the breakdown of the Antarctic circumpolar vortex using TOMS ozone data

Climatological analysis of data from the Total Ozone Mapping Spectrometer (TOMS) on the Nimbus 7 satellite has shown that the annual cycles of ozone are very different in the Arctic and Antarctic. The annual cycle in the Arctic is a relatively smooth annual sine wave; but in the Antarctic the circumpolar vortex breaks down rapidly during the Southern Hemisphere spring (September through November), producing a rapid rise in total ozone and a sawtooth-shaped annual cycle. The evolution of the Antarctic total ozone field during the vortex breakdown was studied by computing areally-integrated ozone amounts from the TOMS data. This technique avoids substantial difficulties with using zonally-averaged ozone amounts to study the asymmetric breakdown phenomenon. Variability of total ozone is found to be large both within an individual year and between different years. During the last decade monthly-mean total ozone values in the Antarctic during the springtime vortex breakdown period have decreased dramatically. The ozone-area statistics indicate that the decrease has resulted in part from changes in the timing of the vortex breakdown and resultant ozone increase, which have occurred later during recent years. Analysis of the spatial scales involved in the ozone transport and mixing that occur during the vortex breakdown is now underway. Reliable calculation of diagnostic quantities like areally-integrated ozone is possible only with the high-resolution, two-dimensional, daily coverage provided by the TOMS instrument.

Bowman, Kenneth P.↗
NASA NTRS1990

Aerodynamic parameters of High-Angle-of attack Research Vehicle (HARV) estimated from flight data

Aerodynamic parameters of the High-Angle-of-Attack Research Aircraft (HARV) were estimated from flight data at different values of the angle of attack between 10 degrees and 50 degrees. The main part of the data was obtained from small amplitude longitudinal and lateral maneuvers. A small number of large amplitude maneuvers was also used in the estimation. The measured data were first checked for their compatibility. It was found that the accuracy of air data was degraded by unexplained bias errors. Then, the data were analyzed by a stepwise regression method for obtaining a structure of aerodynamic model equations and least squares parameter estimates. Because of high data collinearity in several maneuvers, some of the longitudinal and all lateral maneuvers were reanalyzed by using two biased estimation techniques, the principal components regression and mixed estimation. The estimated parameters in the form of stability and control derivatives, and aerodynamic coefficients were plotted against the angle of attack and compared with the wind tunnel measurements. The influential parameters are, in general, estimated with acceptable accuracy and most of them are in agreement with wind tunnel results. The simulated responses of the aircraft showed good prediction capabilities of the resulting model.

Klein, Vladislav↗
NASA NTRS1991

Mixing and non-equilibrium chemical reaction in a compressible mixing layer

The effects of compressibility, chemical reaction exothermicity, and non-equilibrium chemical modeling in a reacting plane mixing layer were investigated by means of two dimensional direct numerical simulations. The chemical reaction was irreversible and second order of the type A + B yields Products + Heat. The general governing fluid equations of a compressible reacting flow field were solved by means of high order finite difference methods. Physical effects were then determined by examining the response of the mixing layer to variation of the relevant non-dimensionalized parameters. The simulations show that increased compressibility generally results in a suppressed mixing, and consequently a reduced chemical reaction conversion rate. Reaction heat release was found to enhance mixing at the initial stages of the layer growth, but had a stabilizing effect at later times. The increased stability manifested itself in the suppression or delay of the formation of large coherent structures within the flow. Calculations were performed for a constant rate chemical kinetics model and an Arrhenius type kinetic prototype. The choice of the model was shown to have an effect on the development of the flow. The Arrhenius model caused a greater temperature increase due to reaction than the constant kinetic model. This had the same effect as increasing the exothermicity of the reaction. Localized flame quenching was also observed when the Zeldovich number was relatively large.

Steinberger, Craig J.↗
NASA NTRS1991

Hydrodynamical instabilities and mixing in SN 1987A - Two-dimensional simulations of the first 3 months

Results are presented from numerical simulations of the early stages of the explosion of SN 1987A. Using a two-dimensional cylindrical geometry version of a smooth particle hydrodynamics code, the explosion is followed for three months to investigate both the early hydrodynamical instabilities and the effect of the subsequent radioactive decay of Ni-56 and Co-56 with half-lives of 6.1 and 77.8 days, respectively. It is shown that the mixing induced by hydrodynamical instabilities occurring during the first few hours is substantially modified at later time by the radioactive decay of Ni-56 and Co-56. The inner cavity of the expanding supernova remnant fills up with nickel, its decay products thus forming a giant 'nickel bubble'. The peak velocity of the nickel increases by approximately 30 percent after the decays. While these results adequately model the core of the observed Fe line profiles, they fail to reproduce the high velocity wings of the spectra.

Herant, Marc↗
NASA NTRS1992

Thermonuclear runaways in nova outbursts

Results of exploratory, two-dimensional numerical calculations of a local thermonuclear runaway on the surface of a white dwarf are reported. It is found that the energy released by the runaway can induce a significant amount of vorticity near the burning region. Such mass motions account naturally for mixing of core matter into the envelope during the explosion. A new mechanism for the lateral spread of nuclear burning is also discussed.

Shankar, Anurag↗
NASA NTRS2020

Face- and Cell-Averaged Nodal-Gradient Approach to Cell-Centered Finite-Volume Method on Mixed Grids

In this paper, the averaged nodal-gradient approach previously developed for triangular grids is extended to mixed triangular-quadrilateral grids. It is shown that the face- averaged approach leads to deteriorated iterative convergence on quadrilateral grids. To develop a convergent solver, we consider cell-averaging instead of face-averaging for quadri- lateral cells. We show that the cell-averaged approach leads to a convergent solver and can be efficiently combined with the face-averaged approach on mixed grids. The method is demonstrated for various inviscid and viscous problems from low to high Mach numbers on two-dimensional mixed grids.

Nishikawa, Hiroaki↗
NASA NTRS1974

Multiringed basins - Illustrated by Orientale and associated features

Geologic mapping and photographs of the Orientale multiring basin are studied as to origin, size, and nature and distribution of ejecta. Six facies of ejecta are observed around the Cordillera Mountains: concentric, radial, smooth plains, grooved, secondary impact craters, and fissured. Transport of these ejecta occurred by block gliding, landsliding, debris flow, and possibly by base surge, viscous flow, and ballistic ejection. The ejecta are mainly clastic types, but melts and annealed breccias are expected to be abundant. Mixing of ejecta and substrate materials must have occurred; compositions of the ejecta are probably zoned laterally and vertically.

Moore, H. J.↗