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At least 721 records · Page 40

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NASA NTRS1975

A new plasma regime in the distant geomagnetic tail

Observations are reported of an extensive region of low-energy plasma particles (LEP) flowing antisunward along the ordered field lines in the lobes of the geomagnetic tail at lunar distances. The flow was detected by three suprathermal ion detectors deployed on the lunar surface during the Apollo 12, 14, and 15 missions. This particle regime is found to be similar to the 'boundary layer' and 'plasma mantle' observed at smaller geocentric distances and to an interior flow region parallel to the magnetopause in the dayside magnetosphere. It is located exterior to the plasma sheet across essentially the entire tail and adjacent to the magnetopause on both the dawn and dusk sides of the magnetosphere. Variations in the integral flux, temperature, and number density are described. It is suggested that this flow and the three similar regimes are simply connected along the inner surface of the magnetopause and are, in fact, the same phenomenon.

Hardy, D. A.↗

NASA NTRS1975

Duct liner optimization for turbomachinery noise sources

An acoustical field theory for axisymmetric, multisectioned lined ducts with uniform flow profiles was combined with a numerical minimization algorithm to predict optimal liner configurations having one, two, and three sections. Source models studied include a point source located on the axis of the duct and rotor/outlet-stator viscous wake interaction effects for a typical research compressor operating at an axial flow Mach number of about 0.4. For this latter source, optimal liners for equipartition-of energy, zero-phase, and least-attenuated-mode source variations were also calculated and compared with exact results. It is found that the potential benefits of liner segmentation for the attenuation of turbomachinery noise is greater than would be predicted from point source results. Furthermore, effective liner design requires precise knowledge of the circumferential and radial modal distributions.

Lester, H. C.↗

NASA NTRS1977

Film cooling on the pressure surface of a turbine vane

Film-cooling-air ejection from the pressure surface of a turbine vane was investigated, and experimental data are presented. This investigation was conducted in a four-vane cascade on a J75-size turbine vane that had a double row of staggered holes in line with the primary flow and located downstream of the leading edge region. The results showed that: (1) the average effectiveness of film-convection cooling was higher than that of either film cooling or convection cooling separately; (2) the addition of small quantities of film-cooling air always increased the cooling effectiveness relative to the zero-injection case; however, (3) the injected film must exceed a certain threshold value to obtain a beneficial effect of film cooling relative to convection cooling alone.

Gauntner, J. W.↗

NASA NTRS1979

Balloon-borne ultraviolet stellar spectrograph. I - Instrumentation and observation. II - Highlights of first observational results

A dual star-tracking system and a system including a telescope, an echelle spectrograph, and a SEC vidicon are the chief components of the Balloon-borne Ultraviolet Stellar Spectrograph (BUSS), which has flown four successful missions. The BUSS missions have yielded 81 spectra for 56 stars, recorded with a resolution of 0.1 A in the wavelength range from 2200 to 3400 A. BUSS observations include: profiles of Mg II lines indicating considerable mass flow in early-type supergiants; Mg II features suggesting a cool expanding outer shell above a hotter chromosphere; emission features in Zeta Tau (a shell star) indicating infalling material; and emission features of the Be star Phi Per suggesting mass outflow.

Kondo, Y.↗

NASA NTRS1979

High-acceleration mass drivers

High-acceleration mass drivers are discussed including the MD2 model of axial geometry, with individually powered drive coils of 13.1 cm diameter. Timing is derived through the interruption of light beams by the moving armature (bucket). Electric power is provided by the resonant discharge of sector capacitor banks through silicon-controlled rectifiers in a two-phase, quadrature circuit. The bucket flies in vacuum, guided by passive dynamic eddy-current magnetic forces, those currents flowing in strip conductors lining the inside of a nonconducting vacuum pipe. Quantitative measurements are obtained with a solid bucket carrying two superconducting coils with a current density of 25 kA/sq cm. A cryogenic station for cooling the bucket to liquid helium temperature is connected to the vacuum pipe.

Oneill, G. K.↗

NASA NTRS1980

Activated solar filaments and flares

Skylab observations have shown that activations and disruptions of dark H-alpha filaments are one of the basic and most important mechanisms of solar activity. The Kopp-Pneuman theory of post-flare loops shows that the process which disrupts a filament opens the magnetic field and causes a greatly enhanced mass flow along the field lines. The open field lines subsequently reconnect, starting from the bottom of the corona and proceeding upwards. This process can last for many hours. Hot loops are first seen in X-rays, then in extreme UV lines, and, after an appropriate cooling time, in H-alpha as the loop prominence systems.

Svestka, Z.↗

NASA NTRS1980

Spin prediction techniques

The NASA Langley Research Center has the responsibility to advance the state-of-the-art in the area of stall/spin technology. This includes the development and validation of experimental and analytical techniques for the prediction of stall/spin characteristics. As a part of this effort, a rotary balance facility located in the Langley spin tunnel was developed two and a half years ago to rapidly identify an airplane's aerodynamic characteristics in a rotational flow environment. On-line rotary balance data plots and on-line predicted steady spin modes permit the designer to develop, on site, a configuration highly resistant to spins, or one which has good spin characteristics, i.e., no spin equilibrium conditions possible with lateral-directional controls neutral, if the airplane is to be used for acrobatic maneuvers or training. The rotary balance data are also used to compute time histories of a spin's incipient, developed, and recovery phases. These spin analysis techniques and their correlation with spin tunnel model and full-scale flight results are discussed herein.

Bihrle, W., Jr.↗

NASA NTRS1981

Energization of ionospheric ions by electrostatic hydrogen cyclotron waves

Interactions between ionospheric ions and electrostatic hydrogen cyclotron waves are studied numerically in an investigation of a possible mechanism for the energization of the low-energy ionospheric ions flowing along geomagnetic field lines to high altitudes. Ion equations of motion are solved numerically for a given number of O(+), He(+) and He(2+) ions initially in a Maxwellian distribution. All the ions considered are found capable of undergoing stochastic acceleration by a coherent electrostatic hydrogen cyclotron wave with parameters typical of the auroral plasma above 1 earth radius. The fraction of the initial ion population undergoing heating depends strongly on the mass, charge and initial temperature of the ion species, with O(+) ions only heated when their initial temperature is approximately greater than the hydrogen temperature and the lighter ions able to be heated even when cold, due to cyclotron resonant stochastic heating.

Singh, N.↗

NASA NTRS1981

The aurora - An electrical discharge phenomenon surrounding the earth

An attempt to model the processes underlying the appearance of auroral phenomena as a chain of events beginning with power production and resulting in auroral light emissions is presented. Power is produced by the interaction of the solar wind with the earth magnetosphere, creating a dynamo effect which is a function of the solar wind speed and the magnitude and orientation of the solar wind magnetic field. The dynamo power generates the convective motion of magnetospheric plasma, and subsequent magnetic-field aligned currents communicate the dynamo power to the polar ionosphere. The currents close as Pederson currents, and the associated Lorentz force accelerates the ionosphere in the direction of the convective motion. An electric potential structure develops at a few thousand km height, forcing current-carrying electrons to flow down the field lines to the ionosphere, where interactions with atmospheric constituents create auroral displays.

Akasofu, S.-I.↗

NASA NTRS1982

Ultraviolet observations of interacting binary Be stars

Initial results from the analysis of a series of timed, high resolution IUE observations of HR 2142, phi Per, CX Dra, KX An, AU Mon, and TT Hya are presented. The data base for HR 2142 also includes Copernicus U1 and U2 observations. Variable absorption lines, indicative of mass flow in the system, are observed in all objects except phi Per. Evidence was also found of mass outflow in the form of winds and/or discrete components. Variable N V absorption was observed in CX Dra and AU Mon and emission features in KX And and phi Per (C IV only). U1 data reveals the presence of complex structure in the gas stream in HR 2142. These observations are compared with those of Be stars which are not thought to be interacting binaries.

Peters, G. J.↗

NASA NTRS1983

On scaling the magnetic field strength in interstellar clouds Resolution of the 'B versus n dilemma'

Attention is given to the 'B versus n dilemma' associated with the near constancy of magnetic field strength based on H I Zeeman data over a range of gas densities. The problem is examined in terms of preferential mass flow along magnetic field lines resulting from the low thermal energy of these regions. Approximate relations have been found to scale the magnetic field strength in interstellar clouds. It is noted that the fiducial gas density for scaling the increasing magnetic field strength is 2-3 orders of magnitude above the average interstellar density often used to estimate B.

Fleck, R. C., Jr.↗

NASA NTRS1984

Energization of ions in the auroral plasma by broadband waves - Generation of ion conics

Nonresonant heating of plasma ions flowing along geomagnetic field lines by VLF waves is shown to generate ion conics. Ions with energies of less than 1 eV are proven capable of resonance with ionospheric VLF waves excited by electron beams with energies over 100 eV at lower hybrid frequencies (LHF) of 1-1.01. The variation of resonant ion energy with LHF wave frequency is formulated and an expression is derived for the heating rate. The heating rate is then applied to model ion acceleration along a dipole geomagnetic field in terms of the power spectral density of broadband waves, i.e., the VLF noise. Attention is given to ion energization at lower altitudes than the auroral acceleration region and examples of conic acceleration are cited.

Singh, N.↗

NASA NTRS1985

Frequency response of a jet engine test facility air supply system

The frequency response of a laboratory scale model of a portion of the air supply system of an engine test facility is obtained both experimentally and using one-dimensional, small-signal, distributed parameter theory. The effects of line terminations and mean flow are considered. Good agreement between experiment and theory is obtained. Predictions are extended to a full scale test facility air supply system operating under several possible test conditions.

Franke, M. E.↗

NASA NTRS1986

Magnetized thermal conduction fronts

The evolution of planar thermal conduction fronts in the presence of a dynamically weak, but otherwise self-consistent, magnetic field is considered. The field is assumed to be connected and untangled. In the diffusion limit for the thermal conductivity, these fronts exhibit self-similar behavior, even in the presence of a field. The role of the field is restricted to channeling the heat flux along its lines of force, and it enters into the problem as a dimensionless angle variable. 'Combing' (or opening) of insulating field lines by the evaporative flow is explicitly demonstrated. Unless the field is nearly perpendicular to the front normal in the hot gas, insulating effects are not profound. Self-similarity breaks down if the front becomes saturated, and under certain conditions magnetized saturated conduction fronts cannot propagate: the solution characteristics of the wave equation form caustics. The physical resolution is the advent of two-fluid (nonlocal) heating. Such Coulomb-heated fronts are expected to be relatively rare in typical astrophysical systems. The large-scale effects of a magnetic field on cloud evaporation in the interstellar medium are briefly discussed, and it is suggested that these fields preclude the presence of time-independent evaporative solutions. Thermal interfaces may then continue to evolve until radiative cooling halts their development; large tracts of warm 10,000 K gas may result.

Balbus, S. A.↗

NASA NTRS1986

A plasma generator utilizing the high intensity ASTROMAG magnets

The magnet configuration for the proposed particle astrophysics magnet facility (ASTROMAG) on the space station includes a cusp magnetic field with an intensity of a few tesla. With these large magnets (or others) located in the outer ionosphere, many quite interesting and unique plasma physics experiments become possible. First there are studies utilizing the magnet alone to examine the supersonic, sub-Alfvenic interaction with the ambient medium; the scale length for the magnet perturbation is approx. 20 m. The magnetic field geometry when combined with the Earth's and their relative motion will give rise to a host of plasma phenomena: ring nulls, x-points, ion-acoustic and lower-hybrid shocks, electron heating (possible shuttle glow without a surface) launching of Alfvenwaves, etc. Second, active experiments are possible for a controlled study of fundamental plasma phenomena. A controlled variable species plasma can be made by using an RF ion source; use of two soft iron rings placed about the line cusp would give an adequate resonance zone (ECH or ICH) and a confining volume suitable for gas efficiency. The emanating plasma can be used to study free expansion of plasma along and across field lines (polar wind), plasma flows around the space platform, turbulent mixing in the wake region, long wavelength spectrum of convecting modes, plasma-dust interactions, etc.

Sullivan, James D.↗

NASA NTRS1986

Theoretical study of the electron temperature in the high-latitude ionosphere for solar maximum and winter conditions

The T(e) variation in the high-latitude ionosphere at altitudes between 120 and 800 km has been modeled for solar maximum, winter solstice, and strong magnetic activity conditions. The calculated electron temperatures are consistent with the plasma densities and ion temperatures computed from a time-dependent ionospheric model. Heating rates for both solar EUV and auroral precipitation were included. In general, the predicted UT variation of the electron temperature that results from the displacement between the magnetic and geographic poles is only a few hundred degrees. However, in sunlit trough regions, T(e) hot spots develop, and these hot spots show a marked UT variation, by as much as 2500 K. The dominant parameter controlling the T(e) variation above 200 km is the magnetospheric heat flux into the ionosphere, which is essentially unknown. For realistic values of the magnetospheric heat flux, the maximum electron temperature ranges from 5000 to 10,000 K at 800 km. A magnetospheric heat flux is particularly effective in enhancing trough electron temperatures. In general, the electron heat flux at high altitudes is uniquely related to the electron temperature and gradient, except on auroral field lines where thermoelectric heat flow is important.

Schunk, R. W.↗

NASA NTRS1988

Preliminary In-Flight Boundary Layer Transition Measurements on a 45 Deg Swept Wing at Mach Numbers Between 0.9 and 1.8

A preliminary flight experiment was flown to generate a full-scale supersonic data base to aid the assessment of computational codes, to improve instrumentation for measuring boundary layer transition at supersonic speeds, and to provide preliminary information for the definition of follow-on programs. The experiment was conducted using an F-15 aircraft modified with a small cleanup test section on the right wing. Results are presented for Mach (M) numbers from 0.9 to 1.8 at altitudes from 25,000 to 55,000 ft. At M greater than or = 1.2, transition occurred near or at the leading edge for the clean configuration. The furthest aft that transition was measured was 20 percent chord at M = 0.9 and M = 0.97. No change in transition location was observed after the addition of a notch-bump on the leading edge of the inboard side of the test section which was intended to minimize attachment line transition problems. Some flow visualization was attempted during the flight experiment with both subliming chemicals and liquid crystals. However, difficulties arose from the limited time the test aircraft was able to hold test conditions and the difficulty of positioning the photo chase aircraft during supersonic test points. Therefore, no supersonic transition results were obtained.

Johnson, J. Blair↗

NASA NTRS1988

A simulation study of broadband electrostatic noise in the presence of ionospheric electrons

Ion beams have been observed flowing along magnetic field lines in the earth's plasma sheet boundary layer and are believed to generate intense electrostatic wave activity known as broadband electrostatic noise. Cold electrons of ionospheric origin have also been observed in this same region and it has been shown that the addition of these cold electrons modifies substantially the plasma wave dispersion properties. With cold electrons present, four instabilities can be excited: (1) ion acoustic, (2) electron acoustic, (3) beam resonant, and (4) Buneman two stream. These instabilities can generate waves with large growth rates at frequencies consistent with broadband electro-static noise. Using computer simulations, consideration is given to the wave energy frequency spectra generated by these instabilities, as well as cold electron heating and nonlinear effects on the ion beam.

Schriver, D.↗