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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Conditional sampling technique to test the applicability of the Taylor hypothesis for the large-scale coherent structures

Comparisons of the distributions of large scale structures in turbulent flow with distributions based on time dependent signals from stationary probes and the Taylor hypothesis are presented. The study investigated an area in the near field of a 7.62 cm circular air jet at a Re of 32,000, specifically having coherent structures through small-amplitude controlled excitation and stable vortex pairing in the jet column mode. Hot-wire and X-wire anemometry were employed to establish phase averaged spatial distributions of longitudinal and lateral velocities, coherent Reynolds stress and vorticity, background turbulent intensities, streamlines and pseudo-stream functions. The Taylor hypothesis was used to calculate spatial distributions of the phase-averaged properties, with results indicating that the usage of the local time-average velocity or streamwise velocity produces large distortions.

Hussain, A. K. M. F.↗
NASA NTRS2019

Automatically Finding Ship-Tracks to Enable Large-Scale Analysis of Aerosol-Cloud Interactions

Ship tracks appear as long winding linear features in satellite images and are produced by aerosols from ship exhausts changing low cloud properties. They are one of the best examples of aerosol‐cloud interaction experiments. However, manually finding ship tracks from satellite data on a large scale is prohibitively costly while a large number of samples are required to improve our understanding. Here we train a deep neural network to automate finding ship tracks. The neural network model generalizes well as it not only finds ship tracks labeled by human experts but also detects those that are occasionally missed by humans. It finds more ship tracks than all previous studies combined and produces a map of ship track distributions off the California coast that matches well with known shipping traffic. Our technique will enable studying aerosol effects on low clouds using ship tracks on a large scale, which will potentially narrow the uncertainty of the aerosol‐cloud interactions.

aerosol cloud interactions↗
NASA NTRS1990

Local gravity and large-scale structure

The magnitude and direction of the observed dipole anisotropy of the galaxy distribution can in principle constrain the amount of large-scale power present in the spectrum of primordial density fluctuations. This paper confronts the data, provided by a recent redshift survey of galaxies detected by the IRAS satellite, with the predictions of two cosmological models with very different levels of large-scale power: the biased Cold Dark Matter dominated model (CDM) and a baryon-dominated model (BDM) with isocurvature initial conditions. Model predictions are investigated for the Local Group peculiar velocity, v(R), induced by mass inhomogeneities distributed out to a given radius, R, for R less than about 10,000 km/s. Several convergence measures for v(R) are developed, which can become powerful cosmological tests when deep enough samples become available. For the present data sets, the CDM and BDM predictions are indistinguishable at the 2 sigma level and both are consistent with observations. A promising discriminant between cosmological models is the misalignment angle between v(R) and the apex of the dipole anisotropy of the microwave background.

Juszkiewicz, Roman↗
NASA NTRS1972

The large-scale structure of the solar wind

The large-scale structure of the solar wind is reviewed on the basis of experimental space measurements acquired over approximately the last decade. The observations cover the fading portion of the last solar cycle up through the maximum of the present cycle. The character of the interplanetary medium is considered from the viewpoint of the temporal behavior of the solar wind over increasingly longer time intervals, the average properties of the various solar wind parameters and their interrelationships. Interplanetary-terrestrial relationships and the expected effects of heliographic lattitude and radial distance are briefly discussed.

Wolfe, J. H.↗
NASA NTRS1973

Large-scale variations in the obliquity of Mars.

Large-scale variations in the obliquity of the planet Mars are produced by a coupling between the motion of its orbit plane due to the gravitational perturbations of the other planets and the precession of its spin axis which results from the solar torque exerted on the equatorial bulge of the planet. The obliquity oscillates on a time scale of approximately 120,000 years. The amplitude of this oscillation itself varies periodically on a time scale of 1,200,000 years. The present-day obliquity is approximately 25.1 deg. The maximum possible variation is from about 14.9 to 35.5 deg. Significant climatic effects must be associated with the phenomenon.

Ward, W. R.↗
NASA NTRS1984

A large-scale investigation of V/STOL ground effects

A large-scale ground-effects test of a single jet in hover was conducted as a first-case study for future tests to provide the V/STOL community with an improved data base. The objectives for this single-jet hover test were to (1) document the jet characteristics and then (2) gather the associated force data. These data are then compared with results obtained from existing prediction methods. A conically convergent nozzle was mounted to a turbojet engine, and an 8-ft-diam suckdown-plate model measured the lift-loss forces in ground effect. Jet-exit characteristics (pressure profile, temperature, turbulence, etc.) are documented for several nozzle pressure ratios. Characteristics that may give rise to scale effects are discussed. Results from this first study indicate that small-scale tests, and current prediction methods, will lead to significant errors in the lift-loss estimation of a single-jet configured aircraft, hovering in ground effect.

Christiansen, R. S.↗
NASA NTRS1987

Gravitational lenses and large scale structure

Four possible statistical tests of the large scale distribution of cosmic material are described. Each is based on gravitational lensing effects. The current observational status of these tests is also summarized.

Turner, Edwin L.↗
NASA NTRS1988

A case study of large-scale structure in a 'hot' model universe

Large-scale structure is studied in an Omega(0) = 1 model universe filled with 'hot' dark matter. A particle mesh computer code is used to calculate the development of gravitational instabilities in 64-cubed mass clouds on a 64-cubed three-dimensional grid over an expansion factor of about 1000. The present epoch is identified by matching the slope of the model particle-particle two-point correlation function with that obtained from observations of galaxies, and the model then corresponds to a cubical sample of the universe of about 105/h Mpc on a side. Properties of the simulated universe are investigated by casting the model quantities into observer's coordinates and comparing the results with observations of the spatial and velocity distributions of luminous matter. It is concluded based on simple arguments that current limits on the time of galaxy formation do not rule out 'hot' dark matter.

Centrella, Joan M.↗
NASA NTRS1993

Upper limit on periodicity in the three-dimensional large-scale distribution of matter

A search for large-scale periodicity in the 3D distribution of 268 Mg II QSO absorption systems which are distributed over 60 percent of the sky, at redshifts 0.1-2.0 is presented. The scalar 3D comoving separations of all pairs of absorption systems are calculated, and peaks in the power spectrum of the distribution of those separations are searched for. The present 95-percent confidence upper limit on the amplitude of a possible periodic fluctuation in the density of galaxies is between one-fourth and three-fourths of the amplitude implied by the data of Broadhurst et al. (1990), depending on the extent to which the wavelength varies and the phase of the signal drifts down lines of sight. A description is presented of how QSO absorption systems sample the 3D population of absorbers and how 3D positions can be represented by their scalar separations.

Tytler, David↗
NASA NTRS2011

Experimental Investigation of a Large-Scale Low-Boom Inlet Concept

A large-scale low-boom inlet concept was tested in the NASA Glenn Research Center 8- x 6- foot Supersonic Wind Tunnel. The purpose of this test was to assess inlet performance, stability and operability at various Mach numbers and angles of attack. During this effort, two models were tested: a dual stream inlet designed to mimic potential aircraft flight hardware integrating a high-flow bypass stream; and a single stream inlet designed to study a configuration with a zero-degree external cowl angle and to permit surface visualization of the vortex generator flow on the internal centerbody surface. During the course of the test, the low-boom inlet concept was demonstrated to have high recovery, excellent buzz margin, and high operability. This paper will provide an overview of the setup, show a brief comparison of the dual stream and single stream inlet results, and examine the dual stream inlet characteristics.

Hirt, Stefanie M.↗
NASA NTRS2002

Large Scale Deformation of the Western U.S. Cordillera

The overall objective of the work that was conducted was to understand the present-day large-scale deformations of the crust throughout the western United States and in so doing to improve our ability to assess the potential for seismic hazards in this region. To address this problem, we used a large collection of Global Positioning System (GPS) networks which spans the region to precisely quantify present-day large-scale crustal deformations in a single uniform reference frame. Our results can roughly be divided into an analysis of the GPS observations to infer the deformation field across and within the entire plate boundary zone and an investigation of the implications of this deformation field regarding plate boundary dynamics.

Bennett, Richard A.↗
NASA NTRS1973

Public attitudes toward programs of large-scale technological changes: Some reflections and policy prescriptions, appendix E

The question of how ready the public is for the implementation of large-scale programs of technological change is considered. Four vital aspects of the issue are discussed which include: (1) the ways in which the public mis-perceives the change process, (2) the ways in which recent history impacts on public attitudes, (3) the ways in which the public divides among itself, and (4) the fundamentals of public attitudes towards change. It is concluded that nothing is so critical in the 1970's to securing public approval for large-scale planned change projects as is securing the approval by change-agents of the public.

Shostak, A. B.↗
NASA NTRS2003

Computation of Large-Scale Structure Jet Noise Sources With Weak Nonlinear Effects Using Linear Euler

An approximate technique is presented for the prediction of the large-scale turbulent structure sound source in a supersonic jet. A linearized Euler equations code is used to solve for the flow disturbances within and near a jet with a given mean flow. Assuming a normal mode composition for the wave-like disturbances, the linear radial profiles are used in an integration of the Navier-Stokes equations. This results in a set of ordinary differential equations representing the weakly nonlinear self-interactions of the modes along with their interaction with the mean flow. Solutions are then used to correct the amplitude of the disturbances that represent the source of large-scale turbulent structure sound in the jet.

Dahl, Milo D.↗
NASA NTRS1993

Average effects of large-scale convection on helioseismic line widths and frequencies

The formalism of Lavely and Ritzwoller (1992) is here applied to the model of stationary large-scale solar convection developed by Glatzmaier (1984) in order to determine a characteristic giant-cell convection signature in helioseismic data. Frequency and line-width measurements are presented on spatially filtered spectra, so that references to azimuthal orders apply to the m-value of the spatial filter's spherical harmonic. Attention is given to the 'Q-bowl' pattern of large-scale convection, a systematic, apparent line-broadening.

Lavely, Eugene M.↗
NASA NTRS1992

Constraints on the power spectrum of the primordial density field from large-scale data - Microwave background and predictions of inflation

It is shown here that, by using galaxy catalog correlation data as input, measurements of microwave background radiation (MBR) anisotropies should soon be able to test two of the inflationary scenario's most basic predictions: (1) that the primordial density fluctuations produced were scale-invariant and (2) that the universe is flat. They should also be able to detect anisotropies of large-scale structure formed by gravitational evolution of density fluctuations present at the last scattering epoch. Computations of MBR anisotropies corresponding to the minimum of the large-scale variance of the MBR anisotropy are presented which favor an open universe with P(k) significantly different from the Harrison-Zeldovich spectrum predicted by most inflationary models.

Kashlinsky, A.↗