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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 1,765 records · Page 98

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NASA NTRS1973

Interaction effects between solar wind and comet Bennett

Observations of the solar wind and the comet Bennett made during the period from Mar. 23 to Apr. 5, 1970 are considered. During this period the position of the comet had been comparatively close to earth at a distance of about 0.7 AU. Plasma data from four space probes and photographs of a number of observatories are taken into account. The relation between a sudden change in the velocity of the solar wind and the occurrence of a pronounced disturbance in the cometary tail is investigated.

Burlaga, L. F.↗

NASA NTRS1975

Development, fabrication and calibration of a porous surface microphone in an aerofoil

The development of a porous surface microphone in an airfoil intended to measure acoustic signals in a turbulent airflow and to minimize the flow noise is described. The sensor because of its airfoil operates over a wide range of yaw angles and flow velocities without excessive flow noise. The acoustic properties of the porous materials used in the airfoil sensor and their effects on the frequency response of the sensor were analyzed and tested. An accurate airfoil was selected, having a smaller thickness-to-chord ratio and an airfoil sensor was designed. The sensor was calibrated acoustically and its flow noise evaluated in the quiet BBN wind tunnel at flow velocities up to 70 m/sec. Results are presented.

Noiseux, D. U.↗

DOE OSTI2015

Powerful, rotating disk winds from stellar-mass black holes

We present an analysis of ionized X-ray disk winds found in the Fe K band of four stellar-mass black holes observed with Chandra, including 4U 1630−47, GRO J1655−40, H 1743−322, and GRS 1915+105. High-resolution photoionization grids were generated in order to model the data. Third-order gratings spectra were used to resolve complex absorption profiles into atomic effects and multiple velocity components. The Fe xxv line is found to be shaped by contributions from the intercombination line (in absorption), and the Fe xxvi line is detected as a spin–orbit doublet. The data require 2–3 absorption zones, depending on the source. The fastest components have velocities approaching or exceeding 0.01c, increasing mass outflow rates and wind kinetic power by orders of magnitude over prior single-zone models. The first-order spectra require re-emission from the wind, broadened by a degree that is loosely consistent with Keplerian orbital velocities at the photoionization radius. This suggests that disk winds are rotating with the orbital velocity of the underlying disk, and provides a new means of estimating launching radii—crucial to understanding wind driving mechanisms. Some aspects of the wind velocities and radii correspond well to the broad-line region in active galactic nuclei (AGNs), suggesting a physical connection. We discuss these results in terms of prevalent models for disk wind production and disk accretion itself, and implications for massive black holes in AGNs.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Intermittent dust mass loss from activated asteroid P/2013 P5 (PANSTARRS)

We present observations and models of the dust environment of activated asteroid P/2013 P5 (PANSTARRS). The object displayed a complex morphology during the observations, with the presence of multiple tails. We combined our own observations, all made with instrumentation attached to the 10.4 m Gran Telescopio Canarias on La Palma, with previously published Hubble Space Telescope images to build a model aimed at fitting all the observations. Altogether, the data cover a full three month period of observations which can be explained by intermittent dust loss. The most plausible scenario is that of an asteroid rotating with the spinning axis oriented perpendicular to the orbit plane and losing mass from the equatorial region, consistent with rotational break-up. Assuming that the ejection velocity of the particles (v ∼ 0.02-0.05 m s{sup –1}) corresponds to the escape velocity, the object diameter is constrained to ∼30-130 m for bulk densities 3000-1000 kg m{sup –3}.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRSDate not supplied

Spatially-Resolved Freestream Velocity Measurements at the NASA Langley 31-Inch Mach 10 Air Tunnel Using FLEET

Freestream velocity measurements in the NASA Langley 31-inch Mach 10 wind tunnel are reported in this paper using Femtosecond Laser Electronic Excitation Tagging (FLEET). The freestream measurements acquired during the January 2023 test campaign were the first direct measurement of freestream velocity in this hypersonic wind tunnel facility. Spatial distributions of time-averaged and instantaneous velocity measurements were obtained at all three typical wind tunnel freestream unit Reynolds number conditions of Re∞/L = 1.8∙106 m-1, 3.6∙106 m-1, and 6.4∙106 m-1, though the current paper focuses on centerline measurements for the three Re∞/L and spatial distributions for one Re∞/L. Measured values for time-averaged velocity and mean of the instantaneous velocity at the wind tunnel centerline agree within 5 m/s or 0.4% of the calculated velocity from the facility data acquisition system. Measurements acquired at locations away from the wind tunnel centerline reveal the spatial extent of the core flow of the hypersonic facility.

FLEET↗

NASA NTRSDate not supplied

Spatially-Resolved Freestream Velocity Measurements at the NASA Langley 31-Inch Mach 10 Air Tunnel Using FLEET

FLEET↗

NASA NTRS1994

Internal motions of HII regions and giant HII regions

We report new echelle observations of the kinematics of 30 HII regions in the Large Magellanic Clouds (LMC), including the 30 Doradus giant HII region. All of the HII regions possess supersonic velocity dispersions, which can be attributed to a combination of turbulent motions and discrete velocity splitting produced by stellar winds and/or embedded supernova remnants (SNRs). The core of 30 Dor is unique, with a complex velocity structure that parallels its chaotic optical morphology. We use our calibrated echelle data to measure the physical properties and energetic requirements of these velocity structures. The most spectacular structures in 30 Dor are several fast expanding shells, which appear to be produced at least partially by SNRs.

Chu, You-Hua↗

NASA NTRS1984

Analysis of Doppler lidar wind measurements

New analysis methods were developed and refined for the synthesis of wind fields from multiple Doppler radar data. Considerable software was written and debugged for wind field synthesis. The analysis methods were applied to radar data collected during the CCOPE experiment in which lidar wind measurements were also made. The analysis method differs from existing methods in that interpolation (using filters with assigned weights) and advection of data, to account for time differential between data acquisition at different points, are not used. Instead, functional fits were used in space and time coordinates to transfer radial velocity data to a space-time grid. Subsequently the wind synthesis is performed. This method gives better space resolution in the synthesized winds, compared to other methods in common use, by better preserving the gradients of velocities. The wind fields show the cellular structure characteristic of boundary-layer convection. Also evident in the analysis are the sharp transitions and gradients in the wind field which were preserved by the synthesis.

Srivastava, R. C.↗

DOE OSTI2011

A RECONNECTION-DRIVEN RAREFACTION WAVE MODEL FOR CORONAL OUTFLOWS

We conduct numerical experiments to determine whether interchange reconnection at high altitude coronal null points can explain the outflows observed as blueshifts in coronal emission lines at the boundaries between open and closed magnetic field regions. In this scenario, a strong, post-reconnection pressure gradient forms in the field-aligned direction when dense and hot, active region core loops reconnect with neighboring tenuous and cool, open field lines. We find that the pressure gradient drives a supersonic outflow and a rarefaction wave develops in both the open and closed post-reconnection magnetic field regions. We forward-model the spectral line profiles for a selection of coronal emission lines to predict the spectral signatures of the rarefaction wave. We find that the properties of the rarefaction wave are consistent with the observed velocity versus temperature structure of the corona in the outflow regions, where the velocity increases with the formation temperature of the emission lines. In particular, we find excellent agreement between the predicted and observed Fe XII 195.119 A spectral line profiles in terms of the blueshift (10 km s{sup -1}), full width at half-maximum (83 mA) and symmetry. Finally, we find that T{sub i} < T{sub e} in the open field region, which indicates that the interchange reconnection scenario may provide a viable mechanism and source region for the slow solar wind.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

Wind farm blockage effects: comparison of different engineering models

The work presents four engineering methods to estimate the induction zone in front of a wind turbine and account for the wind farm blockage effect. The methods comprise the vortex cylinder model, vortex dipole model, self-similar model, and wake projection model. The majority of the models presented account for yaw misalignments and ground effect. Actuator disk simulations are used to verify the individual models. The performance of each model is evaluated both in terms of precision and computational time. The induction models are coupled to wake models within the FLOw Redirection and Induction in Steady State framework to provide the full velocity field within a wind farm. Sample wind farm computations are presented, and the impact of including induction effects into wind farm performance predictions is reported. The different codes are publicly available online.

17 WIND ENERGY↗

DOE OSTI2012

NEAR THE BOUNDARY OF THE HELIOSPHERE: A FLOW TRANSITION REGION

Since April of 2010, Voyager 1 has been immersed in a region of near zero radial flows, where the solar wind seems to have stopped. The existence of this region contradicts current models that predict that the radial flows will go to zero only at the heliopause. These models, however, do not include the sector region (or include it in a kinematic fashion), where the solar magnetic field periodically reverses polarity. Here we show that the presence of the sector region in the heliosheath, where reconnection occurs, fundamentally alters the flows, giving rise to a Flow Transition Region (FTR), where the flow abruptly turns and the radial velocity becomes near zero or negative. We estimate, based on a simulation, that at the Voyager 1 location, the thickness of the FTR is around 7-11 AU.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2012

A Full-Envelope Air Data Calibration and Three-Dimensional Wind Estimation Method Using Global Output-Error Optimization and Flight-Test Techniques

A novel, efficient air data calibration method is proposed for aircraft with limited envelopes. This method uses output-error optimization on three-dimensional inertial velocities to estimate calibration and wind parameters. Calibration parameters are based on assumed calibration models for static pressure, angle of attack, and flank angle. Estimated wind parameters are the north, east, and down components. The only assumptions needed for this method are that the inertial velocities and Euler angles are accurate, the calibration models are correct, and that the steady-state component of wind is constant throughout the maneuver. A two-minute maneuver was designed to excite the aircraft over the range of air data calibration parameters and de-correlate the angle-of-attack bias from the vertical component of wind. Simulation of the X-48B (The Boeing Company, Chicago, Illinois) aircraft was used to validate the method, ultimately using data derived from wind-tunnel testing to simulate the un-calibrated air data measurements. Results from the simulation were accurate and robust to turbulence levels comparable to those observed in flight. Future experiments are planned to evaluate the proposed air data calibration in a flight environment.

Taylor, Brian R.↗

DOE OSTI2013

Kelvin-Helmholtz instability on the magnetopause, magnetohydrodynamic waveguide in the outer magnetosphere, and Alfven resonance deep in the magnetosphere

Oscillations of the 'magnetosphere-solar wind' system are studied analytically in the framework of a plane-stratified model of the medium. The properties of oscillations are determined by three phenomena: Kelvin-Helmholtz instability on the tangential discontinuity (magnetopause) separating the magnetosphere and the solar wind, the presence of a waveguide for fast magnetosonic waves in the magnetosphere, and the Alfven resonance-a sharp increase in the amplitude of oscillations having the properties of Alfven waves-in the inner magnetosphere. The oscillations of the system form a discrete spectrum of eigenmodes. Analytical expressions are obtained for the frequency and growth rate of instability of each mode, as well as for the functions describing the spatial structure of these modes. All these characteristics of the eigenmodes are shown to depend on the velocity of the solar wind as a parameter. The dependences of the main mode characteristics (such as the instability thresholds, the points of the maximum and minimum growth rate, and the spatial distributions of the oscillation energy) on this parameter are determined for each eigenmode.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1974

Theoretical predictions of latitude dependencies in the solar wind

Results are presented which were obtained with the Winge-Coleman model for theoretical predictions of latitudinal dependencies in the solar wind. A first-order expansion is described which allows analysis of first-order latitudinal variations in the coronal boundary conditions and results in a second-order partial differential equation for the perturbation stream function. Latitudinal dependencies are analytically separated out in the form of Legendre polynomials and their derivative, and are reduced to the solution of radial differential equations. This analysis is shown to supply an estimate of how large the coronal variation in latitude must be to produce an 11 km/sec/deg gradient in the radial velocity of the solar wind, assuming steady-state processes.

Winge, C. R., Jr.↗

DOE OSTI2013

DIFFERENTIAL PROPER-MOTION MEASUREMENTS OF THE CYGNUS EGG NEBULA: THE PRESENCE OF EQUATORIAL OUTFLOWS

We present the results of differential proper-motion analyses of the Egg Nebula (RAFGL 2688, V1610 Cyg) based on the archived two-epoch optical data taken with the Hubble Space Telescope. First, we determined that the polarization characteristics of the Egg Nebula are influenced by the higher optical depth of the central regions of the nebula (i.e., the 'dustsphere' of {approx}10{sup 3} AU radius), causing the nebula to illuminate in two steps-the direct starlight is first channeled into bipolar cavities and then scattered off to the rest of the nebula. We then measured the amount of motion of local structures and the signature concentric arcs by determining their relative shifts over the 7.25 yr interval. Based on our analysis, which does not rely on the single-scattering assumption, we concluded that the lobes have been excavated by a linear expansion along the bipolar axis for the past {approx}400 yr, while the concentric arcs have been generated continuously and moving out radially at about 10 km s{sup -1} for the past {approx}5500 yr, and there appears to be a colatitudinally increasing trend in the radial expansion velocity field of the concentric arcs. Numerical investigations into the mass-loss modulation by the central binary system exist, which predict such a colatitudinally increasing expansion velocity field in the spiral-shock trails of the mass-loss ejecta. Therefore, the Egg Nebula may represent a rare edge-on case of the binary-modulated circumstellar environs, corroborating the previous theoretical predictions.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1978

Scintillation observations near the sun

Results on the electron density spectrum, the random velocity and the mean velocity of the solar wind in the region from 5 to 100 solar radii are presented. Results are based on intensity scintillations of incoherent radio sources at different locations and different radio frequencies. The shape of the electron density irregularity spectrum is shown to be well modeled by a power law in wavenumber with a slope that abruptly steepens at higher wavenumbers. This two slope power law model is shown to have a break (defined as the wavenumber of the change of slope) that increases with decreasing distance from the Sun. The fractional random velocity is shown to be insignificant at distances of greater than 40 solar radii, but shows a steady increase with decreasing solar distance inside of 40 solar radii.

Coles, W. A.↗

NASA NTRS2008

Magnetofluid Turbulence in the Solar Wind

The solar wind shows striking characteristics that suggest that it is a turbulent magnetofluid, but the picture is not altogether simple. From the earliest observations, a strong correlation between magnetic fluctuations and plasma velocity fluctuations was noted. The high corrections suggest that the fluctuations are Alfven waves. In addition, the power spectrum of the magnetic fluctuation showed evidence of an inertial range that resembled that seen in fully-developed fluid turbulence. Alfven waves, however, are exact solutions of the equations of incompressible magnetohydrodynamics. Thus, there was a puzzle: how can a magnetofluid consisting of Alfven waves be turbulent? The answer lay in the role of velocity shears in the solar wind that could drive turbulent evolution. Puzzles remain: for example, the power spectrum of the velocity fluctuations is less steep than the slope of the magnetic fluctuations, nor do we understand even now why the solar wind appears to be nearly incompressible with a -5/3 power-spectral index.

Goldstein, Melvyn L.↗

DOE OSTI2015

AN EXTREME HIGH-VELOCITY BIPOLAR OUTFLOW IN THE PRE-PLANETARY NEBULA IRAS 08005-2356

We report interferometric mapping of the bipolar pre-planetary nebula IRAS 08005-2356 (I 08005) with an angular resolution of ∼1″–5″, using the Submillimeter Array, in the {sup 12}CO J = 2–1, 3–2, {sup 13}CO J = 2–1, and SiO J = 5–4 (v = 0) lines. Single-dish observations, using the SMT 10 m, were made in these lines as well as in the CO J = 4–3 and SiO J = 6–5 (v = 0) lines. The line profiles are very broad, showing the presence of a massive (>0.1 M{sub ⊙}), extreme high velocity outflow (V ∼ 200 km s{sup −1}) directed along the nebular symmetry axis derived from the Hubble Space Telescope imaging of this object. The outflow's scalar momentum far exceeds that available from radiation pressure of the central post-AGB star, and it may be launched from an accretion disk around a main-sequence companion. We provide indirect evidence for such a disk from its previously published, broad Hα emission profile, which we propose results from Lyβ emission generated in the disk followed by Raman-scattering in the innermost regions of a fast, neutral wind.

79 ASTRONOMY AND ASTROPHYSICS↗