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Results for “W component of wind velocity”

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 91 records · Page 5
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NASA NTRS1977

Nonlinear Alfven waves in high-speed solar wind streams

A nonlinear proton distribution function that is an exact stationary solution of the nonlinear Vlasov equation and Maxwell's equations and which supports a single nonlinear transverse Alfven (ion cyclotron) wave that is circularly polarized and nondispersive is proposed for most of the observations during high-speed solar wind streams. This nonlinear distribution removes the strong Alfven wave instability, inconsistent with the persistence of the observed proton distribution functions in high-speed streams, found by the linear stability analysis. Model temperature anisotropies and drift velocities of the two spatially inhomogeneous bi-Maxwellian components are consistent with typical proton velocity distributions measured in high-speed streams at 1 AU. Two derived relations for each of the wave number and the phase velocity of the wave are obeyed within experimental uncertainties by two typical proton measurements. Our model also predicts that the alpha particle bulk flow velocity exceeds the proton particle bulk flow velocity, as is observed.

Abraham-Shrauner, B.↗
NASA NTRS1994

Accuracy of the O(+)-O collision cross-section deduced from ionosphere-thermosphere observations

Aeronomic observations applied to the empirical derivation of the ion-neutral collision cross-section -- a basic parameter governing the mutual interaction between the neutral and plasma components in the Earth's upper atmosphere -- have given values considerably larger than those derived from theory. The empirical scheme uses the plasma velocities obtained with the Incoherent Scatter Radar and the neutral winds obtained with the Fabry-Perot Interferometer. It is shown here that such an analysis overestimates the collision cross-section due to the effects of errors in the observables. The effect may be sufficiently large to bring about agreement with theory, and calls for a re-analysis of the aeronomic data using methods which minimize the bias caused by measurement errors.

Reddy, C. A.↗
NASA NTRS1991

Equatorial thermospheric wind changes during the solar cycle - Measurements at Arequipa, Peru, from 1983 to 1990

Near-equatorial thermospheric wind velocities at Arequipa, Peru, are determined over about two-thirds of a solar cycle using Fabry-Perot interferometer measurements of Doppler shifts in the nightglow 630-nm emission line. Mean monthly nocturnal variations in the meridional and zonal wind components are calculated from the nightly data to remove short-term (day-to-day) variability as well as any additional changes introduced by the progression of the solar cycle. For most of the years, at the winter solstice, there is a weak (more than 100 m/s) transequatorial flow from the summer to the winter hemisphere in the early and the late night, with essentially zero velocities in between. At the equinoxes, an early-night poleward (southward) flow at solar minimum (1986) is replaced by an equatorward (northward) flow at solar maximum (1989-1990).

Biondi, M. A.↗
NASA NTRS1991

A simulation study of impulsive penetration of solar wind irregularities into the magnetosphere at the dayside magnetopause

The impulsive penetration processes that occur when a plasma irregularity in the magnetosheath, modeled as a field-aligned filament, impinges on the dayside magnetopause, are investigated via a 2D magnetohydrodynamic code. It is found that, when the magnetic fields of the magnetosheath and magnetosphere are parallel or antiparallel, even plasma filaments with small initial velocities can eventually penetrate through the magnetopause and enter the magnetosphere. If the magnetic fields are not aligned, penetration will occur only if the initial kinetic energy density of the plasma filament is more than 50 times larger than the magnetic energy density due to the transverse component of the magnetic field.

Ma, Z. W.↗
NASA NTRS1993

High-resolution Ca II observations of the local interstellar medium

High-resolution absorption measurements of the interstellar Ca II K line observed toward 46 early-type stars in the local ISM (LISM) are presented. Ca II was detected in 36 of the 46 stars with 82 individual cloud components identified. Ca II was detected to most of the stars closer than 50 pc, except in the region of the Galactic quadrant l = 180-270 degrees which also contains the empty line of sight to B CMa at 220 pc. The mean local standard of rest velocity of the 82 Ca II components implies that the LISM clouds are associated with the motion of the solar neighborhood and not the sun. If the present data are combined with other nearby Ca II component velocities taken from the literature, then a cloud centered approximately at l = 90 deg, b = -40 deg moving coherently with the local interstellar wind vector is supported at a significance level of 99 percent. The Ca II data have been combined with Na I data for the same stars to produce a N(Na I)/N(Ca II) ratio for each identified absorption feature. This ratio plotted against the local standard of rest velocities of the clouds shows that the Routly-Spitzer effect exists down to +/- 10 km/s, which supports grain desorption/destruction models that are efficient at returning calcium to the gas phase at these low velocities.

Vallerga, J. V.↗
NASA NTRS1981

Effects of blade-vane ratio and rotor-stator spacing of fan noise with forward velocity

A research fan stage was acoustically tested in an anechoic wind tunnel with a 41 m/sec tunnel flow. Two stator vane numbers giving cut-on and cut-off conditions were tested at three rotor-stator spacings ranging from about 0.5 to 2.0 rotor chords. These two stators were designed for similar aerodynamic performance. Hot film anemometer turbulence measurements were made at the leading edge of the stator for each spacing. The cut-off criterion strongly controlled the fundamental tone level at all spacings. The trends with spacing of the wake defect upwash component at the stator tip showed good agreement with the corresponding cut-on acoustic tone levels.

Woodward, R. P.↗
NASA NTRS1994

Synthesis of line profiles from models of structured winds

On the basis of a careful analysis of resonance line formation (both for singlets and doublets) in structured winds, present time dependent models of the line driven winds of hot stars are shown to be able to explain a number of observational features with respect to variability and structure: they are (in principle) able to reproduce the black and broad troughs (without any artificial 'turbulence velocity') and the 'blue edge variability' observed in saturate resonance lines: they might explain the 'long lived narrow absorption components' often observed in unsaturated lines at high velocities; they predict a relation between the 'edge velocity' of UV-lines and the radiation temperature of the observed X-ray emission. As a first example of the extent to which theoretical models can be constrained by comparisons between observations and profiles calculated by spectrum synthesis from structured winds, we show here that models with deep-seated onset of structure formation (approximately greater than 1.1 R(sub *)) produce resonance lines which agree qualitatively with observational findings; in contrast, the here presented models with structure formation only well out in the wind (approximately greater than 1.6 R(sub *) fail in this respect.

Puls, J.↗
NASA NTRS1982

A FORTRAN program for calculating three dimensional, inviscid and rotational flows with shock waves in axial compressor blade rows: User's manual

A FORTRAN-IV computer program was developed for the calculation of the inviscid transonic/supersonic flow field in a fully three dimensional blade passage of an axial compressor rotor or stator. Rotors may have dampers (part span shrouds). MacCormack's explicit time marching method is used to solve the unsteady Euler equations on a finite difference mesh. This technique captures shocks and smears them over several grid points. Input quantities are blade row geometry, operating conditions and thermodynamic quanities. Output quantities are three velocity components, density and internal energy at each mesh point. Other flow quanities are calculated from these variables. A short graphics package is included with the code, and may be used to display the finite difference grid, blade geometry and static pressure contour plots on blade to blade calculation surfaces or blade suction and pressure surfaces. The flow in a low aspect ratio transonic compressor was analyzed and compared with high response total pressure probe measurements and gas fluorescence static density measurements made in the MIT blowdown wind tunnel. These comparisons show that the computed flow fields accurately model the measured shock wave locations and overall aerodynamic performance.

Thompkins, W. T., Jr.↗
NASA NTRS1975

Development of a laser Doppler system for the detection and monitoring of atmospheric disturbances

A Scanning Laser Doppler Velocimeter System (SLDVS) capable of detecting and monitoring atmospheric disturbances, including wake vortices of landing aircraft and vertical wind profiles in the atmosphere was developed. The SLDVS is a focused, continuous wave, CO2 system that determines the line-of-sight velocities of particles in the focal volume by measuring the Doppler shift created by these particles. At present, the SLDVS is designed to have a range coverage of approximately 2000 ft with a vertical angle coverage of approximately 60 deg. It is also designed to detect Doppler velocities of up to 200 ft/sec with a velocity resolution of approximately 1.8 ft/sec. A complete velocity spectrum is provided by the SLDVS at each point in space at which it is focused. The overall operation and performance of the system and the description of its individual components and data handling capabilities were given.

Jeffreys, H. B.↗
NASA NTRS1993

Evidence for ion jets in the high-speed solar wind

Results of an investigation of shapes of proton and alpha particle velocity distribution functions in the high-speed solar wind for the time period from 1973 to 1987 are presented. It is suggested that a modest amount of heating results from the damping of waves, whereas additional heating and the bulk of the acceleration is associated with the direct conversion of magnetic energy flux to plasma convection and enthalpy flux through the process of magnetic reconnection. The present two-component model of heating and acceleration predicts that the ambient flow of plasma from coronal holes is characterized by a low-speed and a low-mass flux. The proton flux is insufficient to drag alpha particles out of the solar gravitational potential well.

Feldman, W. C.↗
NASA NTRS1980

Zonal and meridional circulation of the lower atmosphere of Venus determined by radio interferometry

The results of the Pioneer Venus differential long-baseline interferometry experiment are presented. The velocity component of the Pioneer probes as they fell to the surface of Venus was calculated from the Doppler shift of the received signal, and the other two orthogonal components were determined by long-baseline interferometry. The ambient wind velocity was about 1 m/s or less near the surface of the planet and about 100 m/s at an altitude of about 65 km at all four probe locations. Strata of high wind shear were found at altitudes of 15, 45, and 60 km. The wind velocity was always directed within a few degrees of due west except at a few km above the surface. The dominant motion of the lower atmosphere seems to be a retrograde zonal rotation, and eddies appear to account for most of the instantaneous meridional velocity. The data suggest that, within the clouds, a thermally driven mean meridional circulation is superimposed upon the much more rapid zonal rotation.

Counselman, C. C., III↗
NASA NTRS1986

A comparison of vertical velocities measured from specular and nonspecular echoes by a VHF radar

For a number of years, there have been doubts about the accuracy of vertical wind velocities measured with quasi-specular reflections from mesosphere-stratosphere-troposphere (MST) radar. The concern has been that the layers producing the quasi-specular reflection process this hypothetical tilt. Because of the quasi-specular reflection process, this hypothetical tilt would control the effective zenith angle of the radar antenna beam so that a small component of the horizontal velocity would be included in what was assumed to be a truly vertical beam. The purpose here is to test the hypothesis that there is an effect on the wind velocities measured on a vertical antenna beam due to a long-term tilting of the stable atmospheric layers that cause quasi-specular reflection. Gravity waves have been observed to cause short-term tilting of turbulent layers and specularly reflecting layers. In both cases, the effect was a wave-like deformation atmospheric layers with a period of a few minutes. This geometry is shown. Because of this influence of gravity waves, it was expected that there would be short-term variations in the vertical velocity.

Green, J. L.↗
NASA NTRS1978

Characteristic electron variations across simple high-speed solar wind streams

The paper deals with electron variations across simple high-speed streams. Comprehensive scans of the shapes of electron distributions measured at the highest bulk speeds confirm the results of Rosenbauer et al. (1976, 1977) and show that the electron velocity distributions can be broken down into a low-energy or core component and a high-energy strongly beamed component. The low-energy component displays many characteristics expected from a fluid: the internal particle coupling necessary to maintain this state must result from both binary Coulomb collisions and wave-particle interactions. The high-energy or halo component displays many characteristics expected to develop in the absence of collisions beyond a certain base radius. These electrons appear to evolve under the primary influence of static interplanetary magnetic and electric fields and, therefore, develop very anisotropic velocity distributions.

Feldman, W. C.↗
NASA NTRS1994

Line profiles variations from atmospheric eclipses: Constraints on the wind structure in Wolf-Rayet stars

Binary systems in which one of the components has a stellar wind may present a phenomenon known as 'wind' or 'atmospheric eclipse', in which that wind occults the luminous disk of the companion. The enhanced absorption profile, relative to the spectrum at uneclipsed orbital phases, can be be modeled to yield constraints on the spatial structure of the eclipsing wind. A new, very efficient approach to the radiative transfer problem, which makes no requirements with respect to monotonicity of the velocity gradient or size of that gradient, is presented. The technique recovers both the comoving frame calculation and the Sobolev approximation in the appropiate limits. Sample computer simulations of the line profile variations induced by wind eclipses are presented. It is shown that the location of the wind absorption features in frequency is a diagnostic tool for identifying the size of the wind acceleration region. Comparison of the model profile variations with the observed variations in the Wolf-Rayet (W-R)+6 binary system V444 Cyg illustrate how the method can be used to derive information on the structure of the wind of the W-R star constrain the size of the W-R core radius.

Auer, L. H.↗
NASA NTRS1986

Further studies with data collected by NASA's airborne Doppler lidar in Oklahoma in 1981

Continued study of the lidar data collected in 1981 has resulted in significant new improvements in the analysis techniques reported by Bluestein et al. (1985) and McCaul (1985). Through comparison of fore- and aft-derived scalar fields of intensity and spectral width, the self-consistency of the lidar moment estimates was assessed. Reflectivity estimates were found to be quite stable and reliable, while spectral widths were prone to become noisy if signal to noise ratio (SNR) fell below 12 dB. In addition, spectral widths contained a significant component due to radial velocity gradients in areas along gust fronts, and these components were different along the fore and aft lines of sight. Significant improvement in agreement between the fore and aft fields of spectral width was obtained by estimating the radial velocity gradient component and then removing it from the raw measured widths to yield only the turbulent portion of the contribution to width. Additional analyses showed that lidar-derived vorticity estimates were consistent with several approximate models of vorticity growth along gust front zones, and with the hypothesis that Helmholtz instability could have been responsible for vortices seen along part of the gust front of 30 June 1981. Computations of divergence transverse to axes through an isolated cumulus congestus indicated that the strongest convergence tended to lie along an axis parallel to the congestus. This and the results of other additional analyses seem to suggest that the lidar winds do indeed accurately reflected the basic features of the real wind field.

Bluestein, H. B.↗
NASA NTRS1974

The rotor systems research aircraft - A flying wind tunnel

The Sikorsky Aircraft division of United Aircraft Corporation is constructing two uniquely designed Rotor Systems Research Aircraft (RSRA). These aircraft will be used through the 1980's to comparatively test many different types of rotors - articulated, hingeless, teetering, and gimballed, as well as advanced rotor concepts, such as reverse velocity and variable diameter rotors. The RSRA combines a new airframe with existing Sikorsky H-3 (S-61) dynamic components. A force measurement system is incorporated to permit accurate evaluation of significant rotor characteristics. Both rotor and fixed-wing control systems are provided, appropriately integrated for operation in the pure helicopter mode, compound helicopter mode, and fixed-wing mode. The RSRA is the first rotary wing aircraft designed with a crew escape system, including a pyrotechnic system to sever the main rotor blades.

Linden, A. W.↗
NASA NTRS1975

Recent developments in dynamic stall

Tests were performed on an airfoil in a low-turbulence subsonic wind tunnel at fixed incidence for different speeds of the wind, the airfoil being in translatory motion normal or parallel to the wind. The resulting aerodynamic forces and moment on the airfoil were measured along with local pressure and skin friction. When the incidence is small and the boundary layer attached, no unsteady effects were observed. However, for a large incidence (16 deg), in the case of boundary layer separation, strong unsteady effects are revealed when the boundary layer is reattached in periodic flow. Reattachment can be explained assuming that for the same value of free stream velocity, the gradient of the modulus of the periodic component of the relative airspeed at the upper surface of the airfoil in a direction normal to this surface is greater than the gradient of the relative air speed at the upper surface when the airfoil is not oscillating.

Mccroskey, W. J.↗
NASA NTRS1999

Rectangular Relief Diffraction Gratings for Coherent Lidar Beam Deflection

LIDAR systems require a light transmitting system for sending a laser light pulse into space and a receiving system for collecting the retro-scattered light, separating it from the outgoing beam and analyzing the received signal for calculating wind velocities. Currently, a shuttle manifested coherent LIDAR experiment called SPARCLE (SPAce Readiness Coherent Lidar Experiment) includes a silicon wedge (or prism) in its design in order to deflect the outgoing beam 30 degrees relative to the incident direction. The intent of this paper is to present two optical design approaches that may enable the replacement of the optical wedge component (in future, larger aperture, post-SPARCLE missions) with a surface relief transmission diffraction grating. Such a grating could be etched into a lightweight, flat, fused quartz substrate. The potential advantages of a diffractive beam deflector include reduced weight, reduced power requirements for the driving scanning motor, reduced optical sensitivity to thermal gradients, and increased dynamic stability.

Cole, H. J.↗