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At least 757 records · Page 42

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NASA NTRS1982

The influence of solar active region evolution on solar wind streams, coronal hole boundaries and geomagnetic storms

Solar and interplanetary data are examined, taking into account the identification of the heliographic longitudes of the coronal source regions of high speed solar wind (SW) streams by Nolte and Roelof (1973). Nolte and Roelof have 'mapped' the velocities measured near earth back to the sun using the approximation of constant radial velocity. The 'Carrington carpet' for rotations 1597-1616 is shown in a graph. Coronal sources of high speed streams appear in the form of solid black areas. The contours of the stream sources are laid on 'evolutionary charts' of solar active region histories for the Southern and Northern Hemispheres. Questions regarding the interplay of active regions and solar wind are investigated, giving attention to developments during the years 1973, 1974, and 1975.

Gold, R. E.↗

NASA NTRS1982

Field-aligned ion streams in the earth's midnight region

Plasma measurements from the University of California at San Diego auroral particles experiment on the geosynchronous Applied Technology Satellite 6 in the midnight region show that the low-energy ion fluxes (1-100 eV) are field aligned and are well characterized as thermal populations (1-10 eV) with a streaming velocity of 30-100 km/s along the magnetic field line. The lowest energies are found prior to injections, on quiet days, with an increase of the streaming velocity evident when an injection occurs near the satellite. Multiple peaks in the ion distribution functions are attributed to the presence of different ions species (H/+/, He/+/, O/+/, O/2+/) streaming at similar velocities, both during quiet times and as the plasma velocity increases in response to an injection.

Olsen, R. C.↗

NASA NTRS1983

Inlet free-stream turbulence effects on diffuser performance

The performance of a subsonic two dimensional diffuser was experimentally evaluated as a function of inlet free-stream turbulence parameters. Anisotropic inlet free-stream turbulence with the eddy axis perpendicular to the flow and parallel to the diverging walls of the diffuser appears to be more effective at transmitting energy to the diverging walls of the diffuser, thereby improving diffuser performance, as compared to isotropic turbulence or anisotropic turbulence with the eddy axis perpendicular to the diverging walls of the diffuser. The pressure recovery of the diffuser was found to be strongly dependent upon the inlet free-stream total turbulence intensity, was independent of eddy size for large eddy dimensions, and was dependent upon eddy size for small eddy dimensions. The improvement in the diffuser's static pressure recovery coefficient at a total included divergence angle of 20 deg, compared to the low inlet turbulence case, was found to be as much as 21 times larger than the pressure loss across the turbulence generators.

Hoffman, J. A.↗

NASA NTRS1983

The structure of a separating turbulent boundary layer. IV - Effects of periodic free-stream unsteadiness

Measurements were obtained of the sinusoidal unsteadiness of the free stream velocity during the separation of the turbulent boundary layer. Data were gathered by single wire and cross-wire, anemometry upstream of flow detachment, by laser Doppler velocimetry to detect the movement of the flow in small increments, and by a laser anemometer in the detached zone to measure turbulence and velocities. The study was restricted to a sinusoidal instability frequency of 0.61 and a ratio of oscillation amplitude to mean velocity of 0.3. Large amplitude and phase variations were found after the detachment, with unsteady effects producing hysteresis in the relationships between flow parameters. The detached shear layer decreased in thickness with increasing free-stream velocity and increases in the Reynolds shear stress. Deceleration of the free stream velocity caused thickening in the shear layer and upstream movement of the flow reversal location. The results are useful for studies of compressor blade and helicopter rotors in transition.

Simpson, R. L.↗

NASA NTRS1983

The structure of a separating turbulent boundary layer. V Frequency effects on periodic unsteady free-stream flows

The results of experimental trials to obtain measurements of the effects of frequency on the sinusoidal variations in the free stream velocity over a separating turbulent boundary layer are reported. An oscillation frequency of 0.596 Hz was examined, in conjunction with a free stream velocity of 10.18 m/sec. Hot-wire anemometers measured the velocity upstream of the separation and the phase-averaged skin friction, while the velocities in the detached flow zone and the downstream velocity were assayed with a laser anemometer. Large amplitude and phase variations developed at the beginning of separation, producing hysteresis in the relationships between flow parameters. Increases in the free stream velocity decreased the detached shear layer thickness, while in the deceleration segment of the cycle the separated shear layer grew thicker. The results are in a frequency range that are significant for axial compressor blades and helicopter blades.

Simpson, R. L.↗

NASA NTRS1983

The influence of free-stream disturbances on low Reynolds number airfoil experiments

The results of an investigation of the influence of free stream disturbances on the lift and drag performance of the Lissaman 7769 airfoil are presented. The wind tunnel disturbance environment is described using hot-wire anemometer and sound pressure level measurements. The disturbance level is increased by the addition of a 'turbulence screen' upstream of the test section and/or the addition of a flow restrictor downstream of the test section. For the Lissaman airfoil it was found that the problems associated with obtaining accurate wind tunnel data at low chord Reynolds numbers (i.e., below 200,000) are compounded by the extreme sensitivity of the boundary layers to the free stream disturbance environment. The effect of free stream disturbances varies with magnitude, frequency content, and source of the disturbance.

Mueller, T. J.↗

NASA NTRS1983

Observations of ion streaming during substorms

The ion beam phenomenon at the plasma sheet boundary is examined for individually identifiable substorms, and the substorm-associated particle phenomena are evaluated in terms of the energy-angle distributions of the plasma population and three-dimensional energetic ion distributions. In all seven cases studied it is found that ion beams streaming earthward and/or tailward are always present at the edge of the plasma sheet adjacent to the tail lobe. Ion beams penetrating into the plasma sheet region with no detectable density gradient are also observed. Beams at tens to hundreds of eV often stream tailward and are often long lasting, suggesting that they may be related to ionospheric sources. Both tailward and earthward streaming beams are detected for ion beams above 1 keV, consistent with an origin from the distant tail, propagation toward earth, and mirroring back under single particle motions.

Lui, A. T. Y.↗

NASA NTRS1984

Velocity and temperature characteristics of two-stream, coplanar jet exhaust plumes

The subsonic jet exhaust velocity and temperature characteristics of model scale, two stream coplanar nozzles were obtained experimentally. The data obtained included the effects of fan to primary stream velocity and temperature ratios on the jet axial and radial flow characteristics. Empirical parameters were developed to correlate the measured data. The resultant equations were shown to be extensions of a previously published single stream jet velocity and temperature correlation.

Vonglahn, U. H.↗

NASA NTRS1984

Symbol-stream Combiner: Description and Demonstration Plans

A system is described and demonstration plans presented for antenna arraying by symbol stream combining. This system is used to enhance the signal-to-noise ratio of a spacecraft signals by combining the detected symbol streams from two or more receiving stations. Symbol stream combining has both cost and performance advantages over other arraying methods. Demonstrations are planned on Voyager 2 both prior to and during Uranus encounter. Operational use is possible for interagency arraying of non-Deep Space Network stations at Neptune encounter.

Hurd, W. J.↗

NASA NTRS1984

Observations of Gulf Stream-induced and wind-driven upwelling in the Georgia Bight using ocean color and infrared imagery

Ocean color and infrared imagery from U2 aircraft and satellite sensors are used to study upwelling interaction between Gulf Stream and continental shelf waters in the Georgia Bight. The photographic data are combined with in situ measurements of currents, chlorophyll, temperature, salinity, coastal winds, and sea-level in observations of five different upwelling events including a near-short wind-driven upwelling caused by topographic effects, three filament-induced upwellings in the Gulf Stream, and a possible meander-induced upwelling event in the Gulf Stream. Chlorophyll distributions are used to trace the circulation and propagation of filaments along the advective routes by which the water moves offshore. Photographic and mooring array measurements of temperature time series are found to provide nearly identical results for the phase speeds of each event. Field measurements of surface pigments, and Nimbus/7 coastal zone color scanner (CZCS) estimates are found to agree well over the range of concentrations 0.1 to 0.7 mg/m to the third. Examples of U2/Ocean Color Scanner and Nimbus 7 CZCS photographs are provided.

Mcclain, C. R.↗

NASA NTRS1984

Velocity and temperature characteristics of two-stream, coplanar jet exhaust plumes

Von Glahn, U.↗

NASA NTRS1985

Preliminary analysis of tone-excited two-stream jet velocity decay

Acoustic research related to jet flows has established that sound, by amplifying the naturally occuring large-scale structures in turbulent shear layers, can cause a more rapidly decay of the jet plume velocity and temperature and an increase in jet spreading rate. One possible application of this sound-flow interaction phenomenon is to future STOL aircraft that may require modified jet plume characteristics in order to reduce the loads and temperatures on the deflected flaps during take-off and landing operations. The tone-excitation effect on the velocity decay of model-scale, two-stream jet plumes is analyzed. Measured data are correlated in terms of parameters that include excitation sound level and outer-to-inner stream velocity ratio. The effect of plume tone-excitation on far-field jet noise is examined and its implication for large-scale two-stream jets is discussed.

Vonglahn, U. H.↗

NASA NTRS1984

Evidence for atmospheric carbon dioxide variability over the Gulf Stream

Two airborne surveys of atmospheric carbon dioxide concentration have been conducted over the Gulf Stream off the east coast of Virginia and North Carolina on September 7-8, 1983. In situ CO2 data were acquired at an aircraft altitude of 300 m on trajectories that transcected the Gulf Stream near 36 deg N 73 deg W. Data show evidence of a CO2 concentration increase by 4 ppm to 15 ppm above the nominal atmospheric background value of 345 ppm. These enhanced values were associated with the physical location of the Gulf Stream prior to the passage of a weak cold front.

Bufton, J. L.↗

NASA NTRS1984

Corotating interplanetary streams and associated ionospheric disturbances at Venus and earth

During the summer of 1979, solar corona structure was such that a sequence of recurrent regions produced a corresponding sequence of corotating solar wind streams with pronounced downstream signatures. One of these stream events passed earth on July 3 and was observed later at Venus late on July 11th, with similar characteristics. Corresponding in situ measurements at earth from the Atmospheric Explorer-E satellite and at Venus from the Pioneer Venus Orbiter are examined for evidence of comparable perturbations of the planetary ionospheres. The passage of the stream shock front is found to be associated with pronounced fluctuations in n(O+) which appear as pronounced local depletion of ion concentrations in both ionospheres. The ionosphere disturbances appear to be closely associated with large variations in the solar wind momentum flux. The implied local ionospheric depletions observed at each planet are interpreted to be the consequence of plasma redistribution, rather than actual depletions of plasma.

Taylor, H.↗

NASA NTRS1985

A leaky magnetohydrodynamic waveguide model for the acceleration of high-speed solar wind streams in coronal holes

It is now reasonably well established that there is a correlation between high-speed solar wind streams and coronal holes. It has been concluded that a significant addition of momentum and/or energy in the region of supersonic flow is needed to explain the observed particle flux and flow speed observed in the high-speed streams. The most likely source of this additional momentum appears to be magnetohydrodynamic (MHD) waves propagating up from the solar surface. The present investigation is concerned with the propagation of MHD waves in a structure of finite transverse size, taking into account the consequences for the acceleration of high-speed solar wind streams. A waveguide solution for a model coronal hole is described, giving attention to a geometric or ray analysis of the slab waveguide, a wave mode analysis, an analytic solution of the dispersion relation for high-frequency waves, and the calculation of the time-averaged wave force.

Davila, J. M.↗

NASA NTRS1985

The effects of anisotropic free-stream turbulence on turbulent boundary layer behavior

The effects of near-isotropic and highly anisotropic free-stream turbulence on mean flow properties of the turbulence structure of turbulent boundary layers in a near zero pressure gradient flow has been experimentally evaluated. Turbulence levels vary from 0.5% to 8.0% and the momentum thickness Reynolds number varies from 800 to 1100. The results indicate that the effects of free-stream turbulence on the classical boundary layer properties for near-isotropic turbulence which have been published by other investigators are similar to the case of highly anisotropic turbulence fields, while the effects of free-stream turbulence on the properties of the turbulent structure within the boundary layer for the case of near-isotropic turbulence are quite different compared to the highly anisotropic case.

Liang-Wei, F.↗

NASA NTRS1986

Destiny of earthward streaming plasma in the plasmasheet boundary layer

The dynamics of the earth's magnetotail have been investigated, and it has become clear that the plasmasheet boundary layer field lines map into the Region I Field-Aligned Currents (FAC) of the auroral zone. It is pointed out that the role of earthward streaming ions in the plasmasheet boundary layer may be of fundamental importance in the understanding of magnetotail dynamics, auroral zone physics, and especially for ionospheric-magnetospheric interactions. The present paper has the objective to evaluate propagation characteristics for the earthward streaming ions observed in the plasmasheet boundary layer. An investigation is conducted of the propagation characteristics of protons in the plasmasheet boundary layer using independent single particle dynamics, and conclusions are discussed. The density of earthward streaming ions found in the plasmasheet boundary layer should include the ring current as well as the auroral zone precipitaiton and inner plasmasheet regions of the magnetosphere.

Green, J. L.↗

NASA NTRS1985

Free jet feasibility study of a thermal acoustic shield concept for AST/VCE application: Dual stream nozzles

The influence of selected geometric and aerodynamic flow variables of an unsuppressed coannular plug nozzle and a coannular plug nozzle with a 20-chute outer stream suppressor were experimentally determined. A total of 136 static and simulated flight acoustic test points were conducted with 9 scale model nozzles. Also, aerodynamic measurements of four selected plumes were made with a laser velocimeter. The presence of the 180 deg shield produced different mixing characteristics on the shield side compared to the unshield side because of the reduced mixing with ambient air on the shielded side. This resulted in a stretching of the jet, yielding a higher peak mean velocity up to a length of 10 equivalent diameters from the nozzle exit. The 180 deg shield in community orientation around the suppressed coannular plug nozzle yielded acoustic benefit at all observer angles for a simulated takeoff. While the effect of shield-to-outer stream velocity ratio was small at angles up to 120 deg, beyond this angle significant acoustic benefit was realized with a shield-to-outer stream velocity ratio of 0.64.

Janardan, B. A.↗