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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 NTRS1983

Large- and small-scale spatial evolution of digitally processed ocean wave spectra from Seasat synthetic aperture radar

The threshold behavior of the azimuth response falloff in Seasat SAR imagery and its implications with respect to existing wave imaging theories is examined. The large-scale spatial evolution of a set of eight SAR image spectra with adjacent spacing of about 100 km, spanning about 700 km along the satellite orbit is considered. The small-scale evolution of a sequence of 23 spectra with adjacent spacing of about 2.2 km, spanning only about 48 km but experiencing depth changes from 200 to 35 m as well as unknown currents in the vicinity of the continental shelf is studied. The large-scale spatial evolution of the spectrum is generally consistent with the location of wave-generating sources, even when multiple wave systems are present. On a more local scale, the nearshore wave number spectrum responds to local depth changes but is too noisy to respond reliably to local current changes.

Beal, R. C.↗
NASA NTRS1973

Numerical simulation of small-scale thermal convection in the atmosphere

A Boussinesq system is integrated numerically in three dimensions and time in a study of nonhydrostatic convection in the atmosphere. Simulation of cloud convection is achieved by the inclusion of parametrized effects of latent heat and small-scale turbulence. The results are compared with the cell structure observed in Rayleigh-Benard laboratory conversion experiments in air. At a Rayleigh number of 4000, the numerical model adequately simulates the experimentally observed evolution, including some prominent transients of a flow from a randomly perturbed initial conductive state into the final state of steady large-amplitude two-dimensional rolls. At Rayleigh number 9000, the model reproduces the experimentally observed unsteady equilibrium of vertically coherent oscillatory waves superimposed on rolls.

Somerville, R. C. J.↗
NASA NTRS1998

A Theoretical and Observational Study of Large and Small-Scale Dynamics in the Mesosphere and Lower Thermosphere in Support of TIMED

The long-term objectives of this IDS component of the TIMED mission are to define, through a combination of modeling and data analysis efforts, the influences of large- and small-scale waves (tidal, planetary, and gravity waves) on the circulation, structure, composition, and variability of the mesosphere and lower thermosphere. Particular emphasis is aimed at the TIMED core science objectives of defining the structure and energetics of the TIMED core region, approx. 60 to 180 km. To do so, however, it is also essential to understand the dynamical influences and contributions because of their considerable direct and indirect influences on structure and energetics. To accomplish these goals, we anticipate two parallel modeling efforts and a significant data analysis effort following TIMED launch. The modeling efforts will address both: the residual circulation response to mean and variable wave forcing of the MLT through development of a spherical model addressing balanced flow dynamics and transience and a more comprehensive effort addressing gravity wave propagation, interactions, nonlinearity, and spectral evolution and transports in canonical and realistic environments. The data analysis effort is envisioned to involve application of ground-based measurements and TIMED data analyses to a quantification of gravity wave forcing and effects at one or more sites with comprehensive measurement suites and extension of the inferred forcing globally, based on distributed ground-based measurements. Research results and publications resulting from the research are included.

Fritts, David C.↗
NASA NTRS2016

Transient, Small-Scale Field-Aligned Currents in the Plasma Sheet Boundary Layer During Storm Time Substorms

We report on field-aligned current observations by the four Magnetospheric Multiscale (MMS) spacecraft near the plasma sheet boundary layer (PSBL) during two major substorms on 23 June 2015. Small-scale field-aligned currents were found embedded in fluctuating PSBL flux tubes near the Separatrix region. We resolve, for the first time, short-lived earthward (downward) intense field-aligned current sheets with thicknesses of a few tens of kilometers, which are well below the ion scale, on flux tubes moving equatorward earth ward during outward plasma sheet expansion. They coincide with upward field-aligned electron beams with energies of a few hundred eV. These electrons are most likely due to acceleration associated with a reconnection jet or high-energy ion beam-produced disturbances. The observations highlight coupling of multiscale processes in PSBL as a consequence of magnetotail reconnection.

Nakamura, R.↗
NASA NTRS1993

Small-scale density irregularities in the nightside Venus ionosphere - Comparison of theory and observations

The theory of the lower-hybrid-drift instability is compared with observations of plasma density irregularities. Marginal stability boundaries (gamma = 0) for the lower-hybrid-drift instability and the occurrence of small-scale density fluctuations are presented as a function of magnetic field B and density n. For plasma density gradient scale lengths in the range 2-10 km, 80-85 percent of the density fluctuations lie in the unstable B/n parameter regime (gamma greater than 0). Stability boundaries for the onset of instability at a wavelength for which the Pioneer Venus Orbiter could measure a Doppler-shifted frequency of 100 Hz are presented. The conditions on B and n for instability in this situation are more stringent than those for marginal stability, especially at low densities (n less than or equal to 5000/cu cm). In general, the instability is most likely to be active in regions of low beta: high magnetic field strength and low density, as found in ionospheric holes or troughs.

Huba, J. D.↗
NASA NTRS1994

Small-scale behavior in distorted turbulent boundary layers at low Reynolds number

During the last three years we have conducted high- and low-Reynolds-number experiments, including hot-wire measurements of the velocity fluctuations, in the test-section-ceiling boundary layer of the 80- by 120-foot Full-Scale Aerodynamics Facility at NASA Ames Research Center, to test the local-isotropy predictions of Kolmogorov's universal equilibrium theory. This hypothesis, which states that at sufficiently high Reynolds numbers the small-scale structures of turbulent motions are independent of large-scale structures and mean deformations, has been used in theoretical studies of turbulence and computational methods such as large-eddy simulation; however, its range of validity in shear flows has been a subject of controversy. The present experiments were planned to enhance our understanding of the local-isotropy hypothesis. Our experiments were divided into two sets. First, measurements were taken at different Reynolds numbers in a plane boundary layer, which is a 'simple' shear flow. Second, experiments were designed to address this question: will our criteria for the existence of local isotropy hold for 'complex' nonequilibrium flows in which extra rates of mean strain are added to the basic mean shear?

Saddoughi, Seyed G.↗
NASA NTRSDate not supplied

CFD Modeling of Phase Change and Pressure Drop during Violent Sloshing of Cryogenic Fluid in a Small-Scale Tank

This paper presents the development of a two-phase CFD model that is used to study sloshing of a cryogenic fluid (LN2) undergoing phase change generated by lateral acceleration and its effects on the ensuing heat and mass transfer and pressure drop in a small-scale tank. In this model the interface is captured using the volume-of-fluid (VOF) method [1]. Kinetic-theory based Schrage relation [2] is used for calculating phase change mass transfer at the liquid-vapor interface. Computational results are compared to the data provided by a non-isothermal sloshing experiment with phase change conducted by the University of Tokyo and JAXA in 2018 using liquid Nitrogen in a transparent tank. The effect of different thicknesses of a liquid temperature stratification layer created at the interface on the pressure drop during sloshing was studied experimentally. CFD results for interface movement and tank pressure are presented and compared in this paper to experimental data for the cases with the smallest and largest liquid temperature stratification thickness.

phase change↗
NASA NTRS1990

Analysis of small-scale rotor hover performance data

Rotor hover-performance data from a 1/6-scale helicopter rotor are analyzed and the data sets compared for the effects of ambient wind, test stand configuration, differing test facilities, and scaling. The data are also compared to full scale hover data. The data exhibited high scatter, not entirely due to ambient wind conditions. Effects of download on the test stand proved to be the most significant influence on the measured data. Small-scale data correlated resonably well with full scale data; the correlation did not improve with Reynolds number corrections.

Kitaplioglu, Cahit↗
NASA NTRS1992

An estimate of the relative magnitude of small-scale tracer fluxes

The wind and constituent measurements from the polar aircraft data are used to compute the flux spectra. Although there is variation from flight to flight, the flux spectra generally fit a -2 to -1.5 power law as expected theoretically. This result suggests that tracer fluxes from small scale features do not substantially contribute to the overall tracer budget relative to the fluxes from the larger scales.

Bacmeister, Julio T.↗
NASA NTRS1973

Man made culture interpretation and culture revision of small scale maps

The author has identified the following significant results. A major interstate highway added to the Wilmington, Del., quadrangle by another revision method was determined by the ERTS-1 data to have been misplotted from its true position. In addition to the experiment, where ERTS-1 data is available and small-scale revision is in progress, the ERTS-1 data is routinely being used to make additions and deletions of hydrographic features.

Kosco, W. J.↗
NASA NTRS2011

Small Scale Turbopump Manufacturing Technology and Material Processes

As part of an internal research and development project, NASA Marshall Space Flight Center (MSFC) has been developing a high specific impulse 9,000-lbf LOX/LH2 pump-fed engine testbed with the capability to throttle 10:1. A Fuel Turbopump (FTP) with the ability to operate across a speed range of 30,000-rpm to 100,000-rpm was developed and analyzed. This small size and flight-like Fuel Turbopump has completed the design and analysis phase and is currently in the manufacturing phase. This paper highlights the manufacturing and processes efforts to fabricate an approximately 20-lb turbopump with small flow passages, intricately bladed components and approximately 3-in diameter impellers. As a result of the small scale and tight tolerances of the hardware on this turbopump, several unique manufacturing and material challenges were encountered. Some of the technologies highlighted in this paper include the use of powder metallurgy technology to manufacture small impellers, electron beam welding of a turbine blisk shroud, and casting challenges. The use of risk reduction efforts such as non-destructive testing (NDT) and evaluation (NDE), fractography, material testing, and component spin testing are also discussed in this paper.

Alvarez, Erika↗
NASA NTRS1989

A small-scale plasmoid formed during the May 13, 1985, AMPTE magnetotail barium release

Plasmoids are closed magnetic-loop structures with entrained hot plasma which are inferred to occur on large spatial scales in space plasma systems. A model is proposed here to explain the brightening and rapid tailward movement of the barium cloud released by the AMPTE IRM spacecraft on May 13, 1985. The model suggests that a small-scale plasmoid was formed due to a predicted development of heavy-ion-induced tearing in the thinned near-tail plasma sheet. Thus, a plasmoid may actually have been imaged due to the emissions of the entrained plasma ions within the plasma bubble.

Baker, D. N.↗
NASA NTRS1975

Classification of wetlands vegetation using small scale color infrared imagery

A classification system for Chesapeake Bay wetlands was derived from the correlation of film density classes and actual vegetation classes. The data processing programs used were developed by the Laboratory for the Applications of Remote Sensing. These programs were tested for their value in classifying natural vegetation, using digitized data from small scale aerial photography. Existing imagery and the vegetation map of Farm Creek Marsh were used to determine the optimal number of classes, and to aid in determining if the computer maps were a believable product.

Williamson, F. S. L.↗
NASA NTRS1976

A methodology for small scale rural land use mapping in semi-arid developing countries using orbital imagery. Part 4: Review of land use surveys using orbital imagery outside of the USA

The author has identified the following significant results. Outside the U.S., various attempts were made to investigate the feasibility of utilizing orbital MSS imagery in the production of small scale land use maps. Overall, these studies are not as elaborate or extensive in their scope as the U.S. ones, and generally the non-U.S. investigators have employed nonsophisticated and less expensive techniques. A representative range of studies is presented to demonstrate the approaches and trends dealing with reprocessing, interpretation, classification, sampling, and ground truth procedures.

Vangenderen, J. L.↗
NASA NTRS1972

Small scale analogs of the Cayley Formation and Descarts Mountains in impact associated deposits, part C

The exploration of the Cayley Formation and material of the Descartes Mountains and an understanding of the origin and evolution of these units were primary objectives of the Apollo 16 lunar mission. This section examines several areas associated with impact crater deposits that show small-scale features similar in morphology to the regional characteristics of the Cayley and Descartes units shown in the Apollo 16 photography.

Head, J. W.↗
NASA NTRS1985

Hover and forward flight acoustics and performance of a small-scale helicopter rotor system

A 2.1-m diam., 1/6-scale model helicopter main rotor was tested in hover in the test section of the NASA Ames 40- by 80- Foot Wind Tunnel. Subsequently, it was tested in forward flight in the Ames 7- by 10-Foot Wind Tunnel. The primary objective of the tests was to obtain performance and noise data on a small-scale rotor at various thrust coefficients, tip Mach numbers, and, in the later case, various advance ratios, for comparisons with similar existing data on full-scale helicopter rotors. This comparison yielded a preliminary evaluation of the scaling of helicopter rotor performance and acoustic radiation in hover and in forward flight. Correlation between model-scale and full-scale performance and acoustics was quite good in hover. In forward flight, however, there were significant differences in both performance and acoustic characteristics. A secondary objective was to contribute to a data base that will permit the estimation of facility effects on acoustic testing.

Kitaplioglu, C.↗
NASA NTRS1974

Small scale photo probability sampling and vegetation classification in southeast Arizona as an ecological base for resource inventory

The author has identified the following significant results. The broad scale vegetation classification was developed for a 3,200 sq mile area in southeastern Arizona. The 31 vegetation types were derived from association tables which contained information taken at about 500 ground sites. The classification provided an information base that was suitable for use with small scale photography. A procedure was developed and tested for objectively comparing photo images. The procedure consisted of two parts, image groupability testing and image complexity testing. The Apollo and ERTS photos were compared for relative suitability as first stage stratification bases in two stage proportional probability sampling. High altitude photography was used in common at the second stage.

Johnson, J. R.↗