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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Longitudinal Variation and Waves in Jupiter's South Equatorial Wind Jet

We have conducted a detailed study of the cloud features in the strong southern equatorial wind jet near 7.5 S planetographic latitude. To understand the apparent variations in average zonal wind jet velocity at this latitude [e.g.. 1,2,3], we have searched for variations iIi both feature latitude and velocity with longitude and time. In particular, we focused on the repetitive chevron-shaped dark spots visible on most dates and the more transient large anticyclonic system known as the South Equatorial Disturbance (SED). These small dark spots are interpreted as cloud holes, and are often used as material tracers of the wind field.

Simon-Miller, A. A.↗
NASA NTRS1983

Research on non-planar wall geometries for turbulence control and skin-friction reduction

Eight turbulence-control/drag-reduction concepts under study at NASA Langley Research Center are discussed. These concepts include: slot injection, ion wind, large-eddy breakup devices, riblets, relaminarization, convex curvature, passive porous walls, and rigid wavy walls. Of these concepts, passive porous walls and small wavelength wavy walls are found to increase drag. Riblets, slot injection, and large-eddy breakup devices reduce net turbulent drag, at least for some conditions. The ion wind, relaminarization, and convex curvature studies are still in the early stages and require further work to evaluate their applicability for drag reduction.

Hefner, J. N.↗
NASA NTRS2000

Svalbard: A Window for Understanding Temporal/Spatial Aspects of Solar Wind Coupling to the Magnetosphere and Ionosphere

The research facilities on the Svalbard archepelego provide a unique opportunity for observing the temporal and spatial characteristics of the interaction of the solar wind with the magnetosphere-ionosphere system. The first sounding rockets from the SvdRak range at Ny-Alesund have opened a new perspective for separating temporal and spatial effects. Finding a correlation between observations from the rockets and the Wind satellite located nearly 200 R(sub E) upstream in the solar wind that had a lag time less than the advection time forced consideration of tilted phase planes of the interp1anetary electric field. From this it was deduced that the interaction process has to involve high latitude merging, the interplanetary magnetic field (IMF) B(sub Y) bifurcates the cusp relative to the high latitude source regions in the Northern and Southern Hemispheres, IMF B(sub X) controls the interaction time in each hemisphere, and the small convection cell is driven by opposite hemisphere merging. Studies with 4 satellites in the solar wind have shown that the tilt of the phase plane varies on a minute-by-minute basis and change significantly on time scales of tens of minutes. Images of the cusp at 557.7 nm provide a nearly instantaneous picture of the temporal and spatial characteristics of merging at the magnetopause and show that the process can occur at multiple locations. The rate and location vary with time.

Maynard, Nelson C.↗
NASA NTRS2019

High-fidelity Imaging of the Inner AU Mic Debris Disk: Evidence of Differential Wind Sculpting?

We present new high-fidelity optical coronagraphic imagery of the inner ∼50 au of AU Mic's edge-on debris disk using the BAR5 occulter of the Hubble Space Telescope Imaging Spectrograph (HST/STIS) obtained on 2018 July 26–27. This new imagery reveals that "feature A," residing at a projected stellocentric separation of 14.2 au on the southeast side of the disk, exhibits an apparent "loop-like" morphology at the time of our observations. The loop has a projected width of 1.5 au and rises 2.3 au above the disk midplane. We also explored Transiting Exoplanet Survey Satellite photometric observations of AU Mic that are consistent with evidence of two starspot complexes in the system. The likely co-alignment of the stellar and disk rotational axes breaks degeneracies in detailed spot modeling, indicating that AU Mic's projected magnetic field axis is offset from its rotational axis. We speculate that small grains in AU Mic's disk could be sculpted by a time-dependent wind that is influenced by this offset magnetic field axis, analogous to co-rotating solar interaction regions that sculpt and influence the inner and outer regions of our own Heliosphere. Alternatively, if the observed spot modulation is indicative of a significant misalignment of the stellar and disk rotational axes, we suggest that the disk could still be sculpted by the differential equatorial versus polar wind that it sees with every stellar rotation.

John P. Wisniewski↗
NASA NTRS1977

Critical velocity phenomena and the LTP

When the relative velocity between magnetized plasma and neutral gas exceeds a critical value, the gas-plasma interaction is dominated by collective phenomena which rapidly excite and ionize the neutrals. The interaction of the solar wind with a large cloud (between 10 to the 24th and 10 to the 28th power neutrals) vented from the moon should be of this type. Line radiation from such an interaction can yield an apparent lunar surface brightness rivaling reflected sunlight levels over small areas, if the kinetic-energy flow density of the gas is sufficiently high. The aberrated solar-wind flow past the moon would enhance the visibility of such interactions near the lunar sunrise terminator, supporting the statistical studies which indicate that the 'Lunar Transient Phenomena' (anomalous optical phenomena on the moon) are significantly correlated with the position of the terminator on the lunar surface.

Srnka, L. J.↗
NASA NTRS1981

Full-scale aerodynamic characteristics of a propellar installed on a small twin-engine aircraft wing panel

Full-scale measurements of shaft thrust and torque were made. Wind-tunnel speeds and blade angles were set for full-scale flight conditions. Excellent quality measurements were obtained of the thrust coefficient, the power coefficient, and the propeller efficiency for various values of the advance ratio and the blade incidence angle at 3/4-blade radius. A conventional propeller theory found in the literature was applied to the present results. Although thrust, power, and efficiency were somewhat overpredicted, the advance ratio for maximum efficiency was predicted quite accurately. It was found that, for some conditions, spinner drag could be significant. A simple correction that was based on the spinner base pressure substantially accounted for the changes in efficiency that resulted from this cause.

Barlow, P. R.↗
NASA NTRS1984

Magnetic reconnection and magnetic activity

A large-scale magnetic field extending through a highly conducting tenuous fluid may become distorted on a small scale as a consequence of slow small-scale shuffling of the magnetic lines of force at the boundaries of the tenuous fluid. Any slow wrapping and winding introduced at the boundaries is distributed along the field (at the Alfven speed). It is a curious and little-known fact that such wrapping and winding possesses no static equilibrium (except for a set of solutions of extreme symmetry). The result is neutral-point reconnection of the strains in the field, rapidly dissipating the wrapping and winding. It is suggested that this is the principal cause of the extreme heating that produces the active corona of the sun and other stars. The shuffling of the footpoints of the magnetic field in the photospheric turbulence introduces small-scale wrapping and twisting into the coronal loops. The work done by the turbulence in twisting the fields is dissipated within a matter 10-20 hours by neutral-point reconnection, introducing heat into the corona at a rate of about 10 Mergs/sq cm sec for photospheric turbulence of 0.5 km/sec. It is suggested that this is the basic cause of the X-ray corona.

Parker, E. N.↗
NASA NTRS2020

Instrument Offset Optimization Technique for Airborne Doppler Wind Lidar Profiling Algorithm

This paper presents the instrument offset optimization technique for the Doppler Aerosol Wind Lidar (DAWN) profiling algorithm at NASA Langley Research Center (LaRC). The 2 um Doppler wind Lidar system at LaRC has a long history of research development and airborne campaigns. The core of the wind Lidar data processing is Airborne Wind Profiling Algorithm for Doppler Wind Lidar (APOLO), which was developed at LaRC. The extraction of wind parameters from the airborne Doppler wind Lidar data is challenging due to many factors such as the speed of aircraft, and the errors in instrument installation and calibration. It is unavoidable to prevent the adverse impact of calibration error and instrument installation offset on the performance of wind parameter estimation in the algorithm. Due to the unsteady environment where the data are collected, even a small offset will result in nonsensical results in the parameter estimation process. A brief introduction of APOLO and the overview of the optimization techniques are presented in this paper.

Wind profile↗
NASA NTRS1991

A model for the disc Lyman alpha emission of Uranus

A new efficient radiative transfer algorithm for nonhomogeneous model atmospheres has been applied to the Uranian atmosphere. The contribution of the scatter solar Lyman-alpha to the Uranain emission is of the order of 300 R, and the Rayleigh contribution may reach 450 R for small values of the eddy diffusion coefficient (EDC). The total solar contribution may then reach about 750 R for a solar flux of 2.5 x 10 to the 11th photons/sq cm/s/A. A level of up to 400 R is confirmed in some directions for the interstellar wind contribution. The values of the atmospheric EDC necessary to mimic the observations are 50-100 sq cm/s. A small additional source located on the dayside Uranian atmosphere seems necessary correctly to fit the shape of the limb to limb intensity variation, especially near the limbs. Its contribution to the emergent intensity would range from 100 to 500 R.

Ben Jaffel, L.↗
NASA NTRS1985

Passive remote sensing of stratospheric and mesospheric winds

A passive infrared sensor for remote sounding of the wind field in the stratosphere and mesosphere from near earth orbital spacecraft is described. The sensor utilizes gas correlation spectroscopy and electrooptic phase-modulation techniques to measure winds in the 20-120 km altitude range, temperature, and atmospheric species concentrations. The operation of the sensor is examined. The sensitivity of the sensor is small Doppler shifts in an observed spectrum and the performance of the instrument were evaluated using laboratory simulation and numerical modeling. The data reveal that the sensor's wind measurements should have an accuracy better than 5 m/s and a spatial resolution of 5 km vertical by 150 km horizontal.

Mccleese, D. J.↗
NASA NTRS1985

Development and testing of tip devices for horizontal axis wind turbines

A theoretical and field experimental program has been carried out to investigate the use of tip devices on horizontal axis wind turbine rotors. The objective was to improve performance by the reduction of tip losses. While power output can always be increased by a simple radial tip extension, such a modification also results in an increased gale load both because of the extra projected area and longer moment arm. Tip devices have the potential to increase power output without such a structural penalty. A vortex lattice computer model was used to optimize three basic tip configuration types for a 25 kW stall limited commercial wind turbine. The types were a change in tip planform, and a single-element and double-element nonplanar tip extension (winglets). A complete data acquisition system was developed which recorded three wind speed components, ambient pressure, temperature, and turbine output. The system operated unattended and could perform real-time processing of the data, displaying the measured power curve as data accumulated in either a bin sort mode or polynomial curve fit. Approximately 270 hr of perormance data were collected over a three-month period. The sampling interval was 2.4 sec; thrus over 400,000 raw data points were logged. Results for each of the three new tip devices, compared with the original tip, showed a small decrease (of the order of 1 kW) in power output over the measured range of wind speeds from cut-in at about 4 m/s to over 20 m/s, well into the stall limiting region. Changes in orientation and angle-of-attack of the winglets were not made. For aircraft wing tip devices, favorable tip shapes have been reported and it is likely that the tip devices tested in this program did not improve rotor performance because they were not optimally adjusted.

Gyatt, G. W.↗
NASA NTRS2002

Are Solar Activity Variations Amplified by the QBO: A Modeling Study

Solar cycle activity effects (SCAE) in the lower and middle atmosphere, reported in several studies, are difficult to explain on the basis of the small changes in solar radiation that accompany the 11-year cycle. It is therefore natural to speculate that dynamical processes may come into play to produce a leverage. Such a leverage may be provided by the Quasi-Biennial Oscillation (QBO) in the zonal circulation of the stratosphere, which has been linked to solar activity variations. Driven primarily by wave mean flow interaction, the QBO period and its amplitude are variable but are also strongly influenced by the seasonal cycle in the solar radiation. This influence extends to low altitudes and is referred to as 'downward control'. Small changes in the solar radiative forcing may produce small changes in the period and phase of the QBO, but these in turn may produce measurable differences in the wind field. Thus, the QBO may be an amplifier of solar activity variations and a natural conduit of these variations to lower altitudes. To test this hypothesis, we conducted experiments with a 2D version of our Numerical Spectral Model that incorporates Hines' Doppler Spread Parameterization for small-scale gravity waves (GW). Solar cycle radiance variations (SCRV) are accounted for by changing the radiative heating rate on a logarithmic scale from 0.1% at the surface to 1% at 50 km to 10% at 100 km. With and without SCRV, but with the same GW flux, we then conduct numerical experiments to evaluate the magnitude of the SCAE in the zonal circulation. The numerical results indicate that, under certain conditions, the SCAE is significant and can extend to lower altitudes where the SCRV is small. For a modeled QBO period of 30 months, we find that the seasonal cycle in the solar forcing acts as a strong pacemaker to lock up the phase and period of the QBO. The SCAE then shows up primarily as a distinct but relatively weak amplitude modulation. But with a different QBO period between 30 and 34 (or less than 30, presumably) months, the seasonal phase lock is weak. Solar flux variations in the seasonal cycle then cause variations in the QBO period and phase. These amplify the SCAE to produce relatively large variations in the wind field. The SCAE in this case extends to mid-latitudes.

Mengel, J. G.↗
NASA NTRS1989

Residual interference and wind tunnel wall adaption

Measured flow variables near the test section boundaries, used to guide adjustments of the walls in adaptive wind tunnels, can also be used to quantify the residual interference. Because of a finite number of wall control devices (jacks, plenum compartments), the finite test section length, and the approximation character of adaptation algorithms, the unconfined flow conditions are not expected to be precisely attained even in the fully adapted stage. The procedures for the evaluation of residual wall interference are essentially the same as those used for assessing the correction in conventional, non-adaptive wind tunnels. Depending upon the number of flow variables utilized, one can speak of one- or two-variable methods; in two dimensions also of Schwarz- or Cauchy-type methods. The one-variable methods use the measured static pressure and normal velocity at the test section boundary, but do not require any model representation. This is clearly of an advantage for adaptive wall test section, which are often relatively small with respect to the test model, and for the variety of complex flows commonly encountered in wind tunnel testing. For test sections with flexible walls the normal component of velocity is given by the shape of the wall, adjusted for the displacement effect of its boundary layer. For ventilated test section walls it has to be measured by the Calspan pipes, laser Doppler velocimetry, or other appropriate techniques. The interface discontinuity method, also described, is a genuine residual interference assessment technique. It is specific to adaptive wall wind tunnels, where the computation results for the fictitious flow in the exterior of the test section are provided.

Mokry, Miroslav↗
NASA NTRS2015

Strategic Planning of Efficient Oceanic Flights

The efficiency of oceanic flights is low due to limited navigational and communication equipment, congestion and airspace restrictions. The availability of Automated Dependent Surveillance-Broadcast (ADS-B) and other improvements provides opportunity for better strategic planning of trajectories. Transatlantic flights between US and Europe constitute one of the busiest oceanic airspace regions in the world. This paper examines the benefits of a wind-optimal trajectory concept with a strategic de-confliction component compared to the current flight planning using the North Atlantic Tracks. The methodology generates a wind-optimal route for each aircraft and a strategic reduction in the potential conflicts between aircraft by a combination of small adjustments to departure times and rerouting. The de-confliction is achieved by optimization techniques involving simulated annealing with local gradient searching. The fuel burn for the tracks in today's Organized Track System are compared with the corresponding quantities for the wind-optimized routes to evaluate the potential benefits of flying wind-optimal routes in North Atlantic Airspace. The analysis is based on air traffic between US and Europe during July 2012. The potential fuel savings depend on existing inefficiencies in current flight plans, atmospheric conditions and location of the city-pairs. The paper provides both aggregate results and detailed examination of some of the most popular city-pairs. Results show that strategic planning can improve the efficiency of flight trajectories by 3 to 5 depending on city-pairs and aircraft type. This translates into a potential fuel savings in the range of (420-970) kg per flight for a Boeing 767-300, the most widely used aircraft between the city-pairs in this study.

oceanic operations↗
NASA NTRS2021

Continuum, cyclotron line, and absorption variability in the high-mass X-ray binary Vela X-1

Because of its complex clumpy wind, prominent cyclotron resonant scattering features, intrinsic variability, and convenient physical parameters (close distance, high inclination, and small orbital separation), which facilitate the observation and analysis of the system, Vela X-1 is one of the key systems for understanding accretion processes in high-mass X-ray binaries on all scales. We revisit Vela X-1 with two new observations taken with NuSTAR at orbital phases ∼0.68–0.78 and ∼0.36–0.52, which show a plethora of variability and allow us to study the accretion geometry and stellar wind properties of the system. We follow the evolution of spectral parameters down to the pulse period timescale using a partially covered power law continuum with a Fermi-Dirac cutoff to model the continuum and local absorption. We are able to confirm anti-correlations between the photon index and the luminosity and, for low fluxes, between the folding energy and the luminosity, implying a change of properties in the Comptonising plasma. We were not able to confirm a previously seen correlation between the cyclotron line energy and the luminosity of the source in the overall observation, but we observed a drop in the cyclotron line energy following a strong flare. We see strong variability in absorption between the two observations and within one observation (for the ∼0.36–0.52 orbital phases) that can be explained by the presence of a large-scale structure, such as accretion and photoionisation wakes in the system, and our variable line of sight through this structure.

C. M. Diez↗
NASA NTRS2001

Solar Cycle Variations and Equatorial Oscillations: Modeling Study

Solar cycle activity effects (SCAE) in the lower and middle atmosphere, reported in several studies, are difficult to explain on the basis of the small changes in solar radiation that accompany the 11-year cycle, It is therefore natural to speculate that dynamical processes may come into play to produce a leverage. Such a leverage may be provided by the Quasi-Biennial Oscillation (QBO) in the zonal circulation of the stratosphere, which has been linked to solar activity variations. Driven primarily by wave mean flow interaction, the QBO period and its amplitude are variable but are also strongly influenced by the seasonal cycle in the solar radiation. This influence extends to low altitudes referred to as "downward control". Relatively small changes in solar radiative forcing can produce small changes in the period and phase of the QBO, but this in turn can produce measurable differences in the wind field. Thus, the QBO may be an amplifier of solar activity variations and a natural conduit of these variations to lower altitudes. To test this hypothesis, we conducted experiments with a 2D (two-dimensional) version of our Numerical Spectral Model that incorporates Hines' Doppler Spread Parameterization for small-scale gravity waves (GW). Solar cycle radiance variations (SCRV) are accounted for by changing the radiative heating rate on a logarithmic scale from 0.1 % at the surface to 1 % at 50 km to 10% at 100 km. With and without SCRV, but with the same GW flux, we then conduct numerical experiments to evaluate the magnitude of the SCAE in the zonal circulation. The numerical results indicate that, under certain conditions, the SCAE is significant and can extend to lower altitudes where the SCRV is inconsequential. At 20-km the differences in the modeled wind velocities are as large as 5 m/s. For a modeled QBO period of 30 months, we find that the seasonal cycle in the solar forcing (through the Semi-annual Oscillation (SAO)) acts as a strong pacemaker to lockup the phase and period of the QBO. The SCAE then shows up primarily as a distinct but relatively weak amplitude modulation. But with the QBO period between 30 and 34 (or less than 30, presumably) months, the seasonal phase lock is weak. Solar flux radiance variations in the seasonal cycle then cause variations in the QBO period and phase that amplify the SCAE to produce relatively large variations in the wind field. These variations also extend to mid latitudes.

Mayr, H. G.↗
NASA NTRS2013

A System for Measuring the Sway of the Vehicle Assembly Building

A system was developed to measure the sway of the Vehicle Assembly Building (VAB) at Kennedy Space Center. This system was installed in the VAB and gathered more than one total year of data. The building movement was correlated with measurements provided by three wind towers in order to determine the maximum deflection of the building during high-wind events. The VAB owners were in the process of obtaining new platforms for use in assembling very tall rockets when analysis of the VAB showed that a high wind could move the building sufficiently that an upper platform might impact a rocket. The problem arises because safety requires a relatively small gap between the platform and the rocket, while a large enough gap is needed to ensure that stacking tolerances prevent contact between the rocket and the platform. This only leaves an inch or two (approximately 2 to 5 cm) of total clearance, so when the analysis showed that more than a couple of inches of motion could occur in a high wind, there was a potential for damaging the rocket. The KSC Applied Physics Laboratory was asked to install a system in the VAB that could measure the motion of the building in high winds to determine the actual building sway. The motion of the VAB roof under wind load was measured optically, and under analysis, it was determined that a relatively large-aperture optical system would be required to reduce diffraction effects to less than a small fraction of an inch (approximately mm) at a distance of 500 ft (≈150 m). A 10-in. (approximately 250 mm) telescope was placed on the floor of the building, looking at the ceiling. On the ceiling, a flat plate with three white LEDs was mounted in an "L" shape, such that the telescope was essentially looking at three stars. Software was written to track the motion of these three points using an image processing system. This provided a better than 1/10-in. (approximately 2.5-mm) 2D measurement faster than once a second. Data was downloaded once a month for comparison with the wind tower data. The system was fully operational and provided enough data to show that the VAB will only move 1 in. (approximately 2.5 cm) at the ceiling under 70-knot winds. Adjustable platforms are not required.

Youngquist, Robert↗