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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Preliminary simulations of the large-scale environment during the FIRE cirrus IFO

Large scale forcing (scales greater than 500 km) is the dominant factor in the generation, maintenance, and dissipation of cirrus cloud systems. However, the analyses of data acquired during the first Cirrus IFO have highlighted the importance of mesoscale processes (scales of 20 to 500 km) to the development of cirrus cloud systems. Unfortunately, Starr and Wylie found that the temporal and spatial resolution of the standard and supplemental rawinsonde data were insufficient to allow an explanation of all of the mesoscale cloud features that were present on the 27 to 28 Oct. 1986. It is described how dynamic initialization, or 4-D data assimilation (FDDA) can provide a method to address this problem. The first steps towards application of FDDA to FIRE are also described.

Westphal, Douglas L.↗
NASA NTRS1999

Design and Use of a Large-Scale Liquid Helium Conversion System

A large-scale liquid helium (LHe) to high-pressure (HP) gas conversion system has been implemented at the John F. Kennedy Space Center (KSC). Helium is used by the Space Shuttle, Titan, Atlas, and Delta programs for prelaunch processing, during launch count-down, and for postlaunch securing. The first phase of modifications to the Compressor Converter Facility (CCF), operational in April 1998, allowed the facility to accept bulk liquid helium from tanker containers and to off-load the helium at super-critical pressures. The second phase of modifications, planned to be operational by January 2001, will implement a 227-cubic-meter (m(sup 3)) on-site liquid helium storage system. This paper describes the design and operation of the current system and discusses the design and implementation for the second phase system.

Knudsen, P. N.↗
NASA NTRS2011

Status of the Combined-Cycle Engine Large-Scale Inlet Mode Transition Experiment

The Large-Scale Inlet Mode Transition (LIMX) experiment is currently being conducted in the 10x10 foot supersonic wind tunnel at the NASA Glenn Research Center. The experiment has involved the efforts of a team for over four years to get to the first phase of testing, which is examining the aerodynamic characteristics of the inlet. The LIMX inlet involves dual flowpaths: one to provide flow to a turbine engine and one to provide flow to a dual-mode ramjet/scramjet. A rotating splitter cowl can close off the turbine flowpath, which would occur as the propulsion system transitions from turbine power to ramjet/scramjet power at Mach 4. The first phase of the experiment will simulate the turbine and ramjet/scramjet flows using cold pipes with flow rates controlled by mass-flow plugs. Much of the testing will characterize the performance of the turbine flowpath (total pressure recovery and distortion at the engine face location) as factors such as bleed rates and configuration and vortex generators are varied during the inlet mode transition. The performance of the inlet will also be examined at off-design Mach numbers (2.5-3.0) and at angle-of-attack.

Slater, John W.↗
NASA NTRS2018

Icing Simulation Research Supporting the Ice-Accretion Testing of Large-Scale Swept-Wing Models

The work summarized in this report is a continuation of NASA's Large-Scale, Swept-Wing Test Articles Fabrication; Research and Test Support for NASA IRT contract (NNC10BA05 -NNC14TA36T) performed by Boeing under the NASA Research and Technology for Aerospace Propulsion Systems (RTAPS) contract. In the study conducted under RTAPS, a series of icing tests in the Icing Research Tunnel (IRT) have been conducted to characterize ice formations on large-scale swept wings representative of modern commercial transport airplanes. The outcome of that campaign was a large database of ice-accretion geometries that can be used for subsequent aerodynamic evaluation in other experimental facilities and for validation of ice-accretion prediction codes.

Aerodynamics↗
NASA NTRS1991

Large-scale structure in a texture-seeded cold dark matter cosmogony

This paper studies the formation of large-scale structure by global texture in a flat universe dominated by cold dark matter. A code for evolution of the texture fields was combined with an N-body code for evolving the dark matter. The results indicate some promising aspects: with only one free parameter, the observed galaxy-galaxy correlation function is reproduced, clusters of galaxies are found to be significantly clustered on a scale of 20-50/h Mpc, and coherent structures of over 50/h Mpc in the galaxy distribution were found. The large-scale streaming motions observed are in good agreement with the observations: the average magnitude of the velocity field smoothed over 30/h Mpc is 430 km/sec. Global texture produces a cosmic Mach number that is compatible with observation. Also, significant evolution of clusters at low redshift was seen. Possible problems for the theory include too high velocity dispersions in clusters, and voids which are not as empty as those observed.

Park, Changbom↗
NASA NTRS1992

Fractals and cosmological large-scale structure

Observations of galaxy-galaxy and cluster-cluster correlations as well as other large-scale structure can be fit with a 'limited' fractal with dimension D of about 1.2. This is not a 'pure' fractal out to the horizon: the distribution shifts from power law to random behavior at some large scale. If the observed patterns and structures are formed through an aggregation growth process, the fractal dimension D can serve as an interesting constraint on the properties of the stochastic motion responsible for limiting the fractal structure. In particular, it is found that the observed fractal should have grown from two-dimensional sheetlike objects such as pancakes, domain walls, or string wakes. This result is generic and does not depend on the details of the growth process.

Luo, Xiaochun↗
NASA NTRS1979

Large-scale turbulent structures in jets and in flows over cavities and their relationship to entrainment and mixing

Large scale structures in jets and in flows over cavities were investigated experimentally to determine their role in entrainment, mixing, and noise production. The presence of these structures resulted in growth of the shear layer and entrainment. Merging of adjacent large scale structures caused the near field pressure signal in excited flows. It is believed that both the entrained fluid as well as its eventual mixing with the jet flow can be controlled by introducing pulsation in the jet flow at a frequency for which the flow is most unstable.

Sarohia, V.↗
NASA NTRS1993

The large-scale morphology of IRAS galaxies

At present, visual inspection is the only method for comparing the large-scale morphologies in the distribution of galaxies to those in model universes generated by N-body simulations. To remedy the situation, we have developed a set of three structure functions (S1, S2, S3) that quantify the degree of large-scale prolateness, oblateness, and sphericity/uniformity of a 3-D particle distribution and have applied them to a volume-limited (less than = 4000 km/s) sample of 699 IRAS galaxies with f sub 60 greater than 1.2 Jy. To determine the structure functions, we randomly select 500 galaxies as origins of spherical windows of radius R sub w, locate the centroid of the galaxies in the window (assuming all galaxies have equal mass) and then, compute the principal moments of inertia (I sub 1, I sub 2, I sub 3) about the centroid. Each S sub i is a function of (I sub 2)/(I sub 1) and (I sub 3)/I sub 1). S1, S2, and S3 tend to unity for highly prolate, oblate, and uniform distributions, respectively and tend to zero otherwise. The resulting 500 values of S sub i at each scale R sub w are used to construct a histogram.

Babul, Arif↗
NASA NTRS1974

Experimental feasibility study of the application of magnetic suspension techniques to large-scale aerodynamic test facilities

Based on the premises that (1) magnetic suspension techniques can play a useful role in large-scale aerodynamic testing and (2) superconductor technology offers the only practical hope for building large-scale magnetic suspensions, an all-superconductor three-component magnetic suspension and balance facility was built as a prototype and was tested successfully. Quantitative extrapolations of design and performance characteristics of this prototype system to larger systems compatible with existing and planned high Reynolds number facilities have been made and show that this experimental technique should be particularly attractive when used in conjunction with large cryogenic wind tunnels.

Zapata, R. N.↗
NASA NTRS1994

The global climate of December 1992-February 1993. Part 2: Large-scale variability across the tropical western Pacific during TOGA COARE

Recently, scientists from more than a dozen countries carried out the field phase of a project called the Coupled-Atmosphere Response Experiment (COARE), devoted to describing the ocean-atmosphere system of the western Pacific near-equatorial warm pool. The project was conceived, organized, and funded under the auspices of the International Tropical Ocean Global Atmosphere (TOGA) Program. Although COARE consisted of several field phases, including a year-long atmospheric enhanced monitoring period (1 July 1992 -- 30 June 1993), the heart of COARE was its four-month Intensive Observation Period (IOP) extending from 1 Nov. 1992 through 28 Feb. 1993. An overview of large-scale variability during COARE is presented. The weather and climate observed in the IOP is placed into context with regard to large-scale, low-frequency fluctuations of the ocean-atmosphere system. Aspects of tropical variability beginning in Aug. 1992 and extending through Mar. 1993, with some sounding data for Apr. 1993 are considered. Variability over the large-scale sounding array (LSA) and the intensive flux array (IFA) is emphasized.

Gutzler, D. S.↗
NASA NTRS2010

Sectors and Large-Scale Magnetic Field Strength Fluctuations in the Heliosheath Near 110 AU: Voyager 1,2009

This paper describes observations of daily averages of the magnetic field strength B and the magnetic polarity measured by Voyager 1 (V1) in the heliosheath during 2009 between 108.5 and 112.1 AU and at heliographic latitude 34. . 4. A negative magnetic polarity sector was observed during 2009 DOY 43.255. A positive polarity sector was observed during 2009 DOY 256.365. We offer the hypothesis that the existence of the two sectors is the result of the displacement of the wavy heliospheric current sheet to the position of V1 as a result of northward flow in the heliosheath. The large size of the sectors is caused by the slow radial motion of the flow observed by V1 in the heliosheath. The distribution of B during 2009 was lognormal, in contrast to the Gaussian distributions observed by V1 in the heliosheath prior to 2009. The large-scale fluctuations of B, described by the distribution of increments of daily averages of B, have a Tsallis distribution with q = 1.6. The large-scale fluctuations of B observed by V1 during 2009 have a multifractal spectrum with the same parameters that V1 observed during 2005 close to the termination shock at 94 AU. These results suggest that the large-scale magnetic fluctuations of B are in a metastable equilibrium state in the heliosheath between 94 AU and 112.1 AU.

Burlaga, L. F.↗
NASA NTRS1987

The topology of large-scale structure. I - Topology and the random phase hypothesis

Many models for the formation of galaxies and large-scale structure assume a spectrum of random phase (Gaussian), small-amplitude density fluctuations as initial conditions. In such scenarios, the topology of the galaxy distribution on large scales relates directly to the topology of the initial density fluctuations. Here a quantitative measure of topology - the genus of contours in a smoothed density distribution - is described and applied to numerical simulations of galaxy clustering, to a variety of three-dimensional toy models, and to a volume-limited sample of the CfA redshift survey. For random phase distributions the genus of density contours exhibits a universal dependence on threshold density. The clustering simulations show that a smoothing length of 2-3 times the mass correlation length is sufficient to recover the topology of the initial fluctuations from the evolved galaxy distribution. Cold dark matter and white noise models retain a random phase topology at shorter smoothing lengths, but massive neutrino models develop a cellular topology.

Weinberg, David H.↗
NASA NTRS2011

Large-Scale Low-Boom Inlet Test Overview

This presentation provides a high level overview of the Large-Scale Low-Boom Inlet Test and was presented at the Fundamental Aeronautics 2011 Technical Conference. In October 2010 a low-boom supersonic inlet concept with flow control was tested in the 8'x6' supersonic wind tunnel at NASA Glenn Research Center (GRC). The primary objectives of the test were to evaluate the inlet stability and operability of a large-scale low-boom supersonic inlet concept by acquiring performance and flowfield validation data, as well as evaluate simple, passive, bleedless inlet boundary layer control options. During this effort two models were tested: a dual stream inlet intended to model potential flight hardware and a single stream design to study a zero-degree external cowl angle and to permit surface flow visualization of the vortex generator flow control on the internal centerbody surface. The tests were conducted by a team of researchers from NASA GRC, Gulfstream Aerospace Corporation, University of Illinois at Urbana-Champaign, and the University of Virginia

Hirt, Stefanie↗
NASA NTRS1978

Coronal hole evolution by sudden large scale changes

Sudden shifts in coronal-hole boundaries observed by the S-054 X-ray telescope on Skylab between May and November, 1973, within 1 day of CMP of the holes, at latitudes not exceeding 40 deg, are compared with the long-term evolution of coronal-hole area. It is found that large-scale shifts in boundary locations can account for most if not all of the evolution of coronal holes. The temporal and spatial scales of these large-scale changes imply that they are the results of a physical process occurring in the corona. It is concluded that coronal holes evolve by magnetic-field lines' opening when the holes are growing, and by fields' closing as the holes shrink.

Nolte, J. T.↗
NASA NTRS1994

Contribution of peculiar shear motions to large-scale structure

Self-gravitating shear flow instability simulations in a cold dark matter-dominated expanding Einstein-de Sitter universe have been performed. When the shear flow speed exceeds a certain threshold, self-gravitating Kelvin-Helmoholtz instability occurs, forming density voids and excesses along the shear flow layer which serve as seeds for large-scale structure formation. A possible mechanism for generating shear peculiar motions are velocity fluctuations induced by the density perturbations of the postinflation era. In this scenario, short scales grow earlier than large scales. A model of this kind may contribute to the cellular structure of the luminous mass distribution in the universe.

Mueler, Hans-Reinhard↗
NASA NTRS1994

Episodic large-scale overturn of two-layer mantles in terrestrial planets

It is usually assumed that the upper and lower mantles of a chemically stratified planet are arranged so that the upper mantle is chemically less dense and that these layers convect separately. Possible buoyant overturn of the two mantle layers has not previously been considered. Such overturn would initially occur when thermal expansion of a chemically denser lower mantle more than offsets the compositional density difference between the layers, reversing the relative sense of buoyancy. Once overturn has occurred, the chemically denser, but thermally less dense upper mantle cools more efficiently than the lower mantle and loses its relative thermal buoyancy. If mixing is slow, this leads to repeated overturns that result in thermal histories that differ radically from those obtained without this large-scale overturning. Thermal evolution calculations, for a two-layer mantle over a wide range of parameter space, show that large-scale overturn occurs cyclically with a well-defined period. This period depends most strongly on the viscosity of the lower mantle, to which it is approximately proportional. Geologically interesting overturn periods on the order of 10(exp 7) to 10(exp 9) years result for lower mantle viscosities of 10(exp 22) to 10(exp 24) Pa s for the Earth and Venus, and 10(exp 21) to 10(exp 23) Pa s for Mars. The mantles of Mercury and the Moon are too thin to permit two-layer convection, and therefore the model is not appropriate for them. Overturn cannot occur on Earth or Venus if the compositional density difference between the layers exceeds about 4%, or on Mars if it exceeds about 2%. Large-scale mantle overturn could have significant tectonic consequences such as the initiation of a new plate tectonic cycle on the Earth or a major resurfacing event on Mars or Venus. Such episodic events in the evolution of a planet are not easily explained by whole mantle thermal convection.

Herrick, David L.↗
NASA NTRS1974

Assessment of the technology required to develop photovoltaic power system for large scale national energy applications

A technical assessment of a program to develop photovoltaic power system technology for large-scale national energy applications was made by analyzing and judging the alternative candidate photovoltaic systems and development tasks. A program plan was constructed based on achieving the 10 year objective of a program to establish the practicability of large-scale terrestrial power installations using photovoltaic conversion arrays costing less than $0.50/peak W. Guidelines for the tasks of a 5 year program were derived from a set of 5 year objectives deduced from the 10 year objective. This report indicates the need for an early emphasis on the development of the single-crystal Si photovoltaic system for commercial utilization; a production goal of 5 x 10 to the 8th power peak W/year of $0.50 cells was projected for the year 1985. The developments of other photovoltaic conversion systems were assigned to longer range development roles. The status of the technology developments and the applicability of solar arrays in particular power installations, ranging from houses to central power plants, was scheduled to be verified in a series of demonstration projects. The budget recommended for the first 5 year phase of the program is $268.5M.

Lutwack, R.↗
NASA NTRS1987

Formation of large-scale structure from cosmic-string loops and cold dark matter

Some results from a numerical simulation of the formation of large-scale structure from cosmic-string loops are presented. It is found that even though G x mu is required to be lower than 2 x 10 to the -6th (where mu is the mass per unit length of the string) to give a low enough autocorrelation amplitude, there is excessive power on smaller scales, so that galaxies would be more dense than observed. The large-scale structure does not include a filamentary or connected appearance and shares with more conventional models based on Gaussian perturbations the lack of cluster-cluster correlation at the mean cluster separation scale as well as excessively small bulk velocities at these scales.

Melott, Adrian L.↗