Search NASA⌕ Search

SEARCH · Search NASA

Results for “outflow”

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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Flight through thunderstorm outflows

Computer simulation of aircraft landing through thunderstorm gust fronts is carried out. The 3 degree-of-freedom, nonlinear equations of aircraft motion for the longitudinal variables containing all two-dimensional wind shear terms are solved numerically. The gust front spatial wind field inputs are provided in the form of tabulated experimental data which are coupled with a computer table lookup routine to provide the required wind components and shear at any given position within an approximate 500 m x 1 km vertical plane. The aircraft is considered to enter the wind field at a specified position under trimmed conditions. Both fixed control and automatic control landings are simulated. Flight paths, as well as control inputs necessary to maintain specified trajectories, are presented and discussed for aircraft having characteristics of a DC-8, B-747, and a DHC-6.

Frost, W.↗
NASA NTRS1980

Modes of sediment transport in channelized water flows with ramifications to the erosion of the Martian outflow channels

The paper discusses application to Martian water flows of the criteria that determine which grain-size ranges are transported as bed load, suspension, and wash load. The results show nearly all sand-sized material and finer would have been transported as wash load and that basalt pebbles and even cobbles could have been transported at rapid rates of suspension. An analysis of the threshold of sediment motion on Mars further indicates that the flows would have been highly competent, the larger flows having been able to transport boulder-sized material. Comparisons with terrestrial rivers which transport hyperconcentration levels of sediments suggest that the Martian water flows could have achieved sediment concentrations up to 70% in weight. Although it is possible that flows could have picked up enough sediment to convert to pseudolaminar mud flows, they probably remained at hyperconcentration levels and fully turbulent in flow character.

Komar, P. D.↗
NASA NTRS1981

Implementation of nonreflective boundary condition at the outflow boundary

Numerical techniques for the solution of free surface flows about a disturbance on or near a free surface were developed. Any disturbance moving on or near a liquid surface generates surface waves that propagate away from the disturbance. The potential flow problems in which the evolution of free surface waves is the principal phenomenon of interest are considered. The distinct feature of these problems is that the position of the surface is also unknown and is to be determined as part of the solution. Two boundary conditions are required at the free surface since there are two unknown functions there, the free surface height and the potential function. The required boundary conditions are satisfied by the kinematic condition which states that no flow can cross the surface and the dynamic condition which matches the fluid pressure to the pressure acting on the surface through Bernoulli's equation.

Hall, D. R.↗
NASA NTRS1981

Origin of Martian outflow channels - The eolian hypothesis

It has been recognized for many years that wind injects dust into the atmosphere on Mars and moves around thin layers of surface material. An investigation is conducted regarding the rates of eolian transport on Mars in the context of eolian channel formation. A model is developed for the formation of an erosional channel by sandblasting with materials transported by wind out of chaotic terrains. This model is applied to the interpretation of topographic measurements made in the chaotic terrain source area and channel of Aromatum Vallis, a small well-preserved channel system southwest of the Chryse basin, and constraints are developed on the eolian mechanism.

Cutts, J. A.↗
NASA NTRS1981

Winds in late-type stars - Mechanisms of mass outflow

The four basic mechanisms that have been proposed for explaining the acceleration of winds in late-type stars are thermal pressure gradients, radiation pressure on circumstellar dust grains, momentum addition by Alfven waves, and momentum addition by periodic shock waves. Recent work in applying these mechanisms to stars is reviewed, with consideration given to whether these mechanisms can work, even in principle, and whether they are consistent with recent ultraviolet and X-ray data from the IUE and Einstein spacecraft. It is noted that thermally driven winds are likely important for late-type dwarfs, where the mass loss rates are small, and perhaps also in G giants and supergiants, but they cannot operate alone in the K and M giants and supergiants. It is thought that radiatively driven winds are probably unimportant for all cool stars, even the M supergiants with dusty circumstellar envelopes. In principle, Alfven waves can accelerate winds to high speeds so long as the field lines are initially open or forced open by some mechanism, but detailed calculations are needed. It is noted that, for the Miras and semiregular variable supergiants, periodic shock waves provide a simple way of producing rapid mass loss.

Linsky, J. L.↗
NASA NTRS1982

Measurements of outflow from the base of solar coronal holes

New evidence is presented that EUV emission lines formed at the levels of the base of the corona and the transition region are systematically shifted to shorter wavelengths within coronal holes relative to the rest of the solar disk, and that moreover this shift increases with height in the atmosphere. Measurements were made with a rocket-borne EUV spectrometer having high spectroscopic resolution and stability flown on July 15, 1980. Repeated measurements were made along a chord of the solar disk that crossed a compact coronal hole near sun center identified on gamma 10830 He I spectroheliograms. The maximum measured shift corresponded to a velocity of 12 km/sec in gamma 625 Mg X and 7 km/sec in gamma 629 O V. If these velocities correspond to a true mass flux, they provide important data on the acceleration of coronal plasma in open magnetic field regions. These observed Doppler displacements are a strong and significant signature of coronal holes, now measured on three rocket flights.

Rottman, G. J.↗
NASA NTRS1983

Outflow from the sun's polar corona

New observations of systematic Doppler shifts of EUV resonance lines formed both in the low corona and transition region are reported. They were made with an improved, high-resolution, stable, rocket-borne spectrometer flown on 1981 November 23. The chord of the solar disk scanned by the spectrometer crossed the north polar cap hole and its low-latitude extension, and also a compact low-latitude hole near sun center. Within both holes, the lines were systematically shifted to shorter wavelengths relative to the rest of the solar disk. These observations strengthen the association of negative Doppler shifts with coronal holes and indicate that this 'blueshift signature', previously observed only within small low-latitude holes, is also characteristic of the low-density polar corona. The mean relative blueshift measured in lambda 625 Mg X (T = 10 to the 6.15 power K) within the polar hole was about 8 km/s.

Orrall, F. Q.↗
NASA NTRS1986

An outflow acoustic boundary condition for internal duct flows

A boundary condition for the linear acoustic equation has been developed that allows the acoustic pressure waves to propagate out of the computational domain boundary, just as they would propagate in an infinitely long duct. The problem is divided into two domains: numerical and analytical. The boundary condition provides a matching of the two domains. Examples show this method works well in an acoustic panel program for a model problem (simple source in a rectangular duct with several propagating modes present). The boundary condition is described so that it can be used with various duct various duct geometries and numerical methods.

Mosher, M.↗
NASA NTRS1988

Debris flows of the Simud-Tiu outflow system of Mars

It is seen that the magnitude of geologic happenings are commonly quite different between the Earth and Mars because of differences in the makeup and breakup of their crusts. By assessing the differences, and the similarities, between planets, the geologic history of Mars can be more fully understood. The identification of debris-flow deposits in channels of Mars, for example, helps to establish which of several competing explanations for the origin of the channels actually occurred. In turn, the Earth is viewed in new, and commonly enlightening perspectives. By the way, it is fortunate that on Earth, thick sequences of impact ejected are not found that could be transformed into the monstrous debris flows that have devastated the Martian surface.

Tanaka, Kenneth L.↗
NASA NTRS1987

Forbidden line and H-alpha profiles in T Tauri star spectra - A probe of anisotropic mass outflows and circumstellar disks

The results of a high-resolution spectroscopic study of 10 T Tauri stars (TTS) and two Herbig emission stars are presented based on red echelle spectra including the lines of forbidden O I 6300 A, forbidden N II 6584 A, forbidden S II 6716, 6731 A, as well as H-alpha. The forbidden lines display a continuous progression of profile types. The velocity structure in the forbidden lines is critically examined and compared to computed line profiles for a number of different wind models. Constant velocity spherical or conical winds fail to reproduce the observed line profiles, which are better explained by a wind with a latitude-dependent velocity field. A prediction of the wind model correlating the velocity of the reversal at H-alpha and the forbidden line velocity structure as a function of the view angle to the star is explored. Estimates of the average densities and sizes for the TTS forbidden emission regions are presented, and mass-loss rates are computed. IRAS far-IR fluxes are used to estimate the disk sizes.

Edwards, Suzan↗
NASA NTRS1988

SiS in Orion-KL - Evidence for 'outflow' chemistry

The J = 6-5 and J = 5-4 rotational transitions at 91 and 109 GHz toward Orion-KL provide evidence for the presence of SiS at an LSR velocity of 7.5 km/sec and with a half-width at zero power of 36 km/sec. The estimated current density corresponds to a fractal abundance of about 4 x 10 to the -9th. The implied SiO/SiS ratio of about 60 is close to the cosmic O/S ratio of about 40 and is much less than that predicted by ion-molecule models. Other unidentified lines near 91 and 109 have been identified.

Ziurys, L. M.↗
NASA NTRS1988

Modelling of time-dependent ion outflows at high geomagnetic latitudes

The output from the NCAR Thermospheric General Circulation Model was used to simulate the time and altitude-dependent F-region ion frictional heating rate. These ion-heating profiles, computed as a functionm of UT along the locus of specific flux tubes, were used as boundary conditions in the Gombosi et al. (1985) polar wind model to simulate the plasma heating history of a flux tube traversing the cusp region. Using derived time-varying frictional heating rates such as those experienced by these flux tubes, it is shown that transverse ion heating below 500 km can provide sufficient energy to perturb the velocity distribution of the major ion species.

Cannata, R. W.↗
NASA NTRS1989

Metamorphism of cosmic dust: Processing from circumstellar outflows to the cometary regolith

Metamorphism of refractory particles continues in the interstellar medium (ISM) where the driving forces are sputtering by cosmic ray particles, annealing by high energy photons, and grain destruction in supernova generated shocks. Studies of the depletion of the elements from the gas phase of the interstellar medium tell us that if grain destruction occurs with high efficiency in the ISM, then there must be some mechanism by which grains can be formed in the ISM. Most grains in a cloud which collapses to form a star will be destroyed; many of the surviving grains will be severely processed. Grains in the outermost regions of the nebula may survive relatively unchanged by thermal processing or hydration. It is these grains which one hopes to find in comets. However, only those grains encased in ice at low temperature can be considered pristine since a considerable degree of hydrous alteration might occur in a cometary regolith if the comet enters the inner solar system. The physical, chemical and isotopic properties of a refractory grain at each stage of its life cycle will be discussed.

Nuth, Joseph A., III↗