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NASA NTRS1980

Stellar winds, fast rotators, and magnetic acceleration

The assumption that observed mass outflow from a star is due to a magnetically driven wind implies an upper bound on the surface magnetic field strength from regions where the wind originates. Evidence is reported that corroborates Rosendhal's observation of an abrupt change in the velocity-gradient-luminosity relationship for B8 and later supergiants. The smallest upper bounds correspond to later spectral types, for which radiation would be a relatively inefficient mechanism for driving wind; these winds may in fact be magnetically driven. Be stars are prime candidates for magnetically accelerated winds due to large rotation rates and small mass loss rates. Observed flows can be driven by 0.1-10 gauss surface fields. Intense field in fast rotators can lead to dramatic mass loss rates and large terminal velocities; sigma Ori E may be such an object. Finally, the effect of magnetic acceleration on the dispersal of solar nebula is considered. The increased velocities allow the wind to disperse a mass of 90 times the initial outflowing mass in the wind.

Nerney, S.↗

NASA NTRS1978

Incoherent scatter radar observations of irregular structure in mid-latitude sporadic E layers

The basic experiments used phase-coded pulses to record electron density profiles with a resolution of 600 m in range and 300 m in horizontal extent, while scanning in azimuth. Data from incoherent scatter radar were compared with simultaneous ionosonde observations. Observations of sporadic E layers by incoherent scatter radar were discussed in terms of the effects of the neutral wind system acting on metallic ions. Several features were noted in the data, which support the wind shear mechanism of layer formation. The sporadic E layers often contained a pronounced small-scale structure, especially at times when partially transparent echoes were observed by the ionosonde. Under specific conditions, the ions in a meteor trail can be converged by a shear in the neutral wind into a relatively small irregularity at the center of a sporadic E layer.

Miller, K. L.↗

NASA NTRS1982

A comparison of wind tunnels suitable for rotorcraft noise studies

Many good small scale facilities are available for rotorcraft noise research. Ames 40 x 80/80 x 120 probably is a good large scale facility for acoustic research of large or small rotorcraft, but the acoustic quality of the modified facility was not yet measured. DNW is probably the best aeroacoustic facility, but may be expensive. Other parameters to consider besides background noise are turbulent level and scale, restructed measurement field, local reflections, and speed range. Advanced measurement techniques improve data quality from any facility.

Soderman, P. T.↗

NASA NTRS1980

Development and flight evaluation of an augmented stability active controls concept with a small tail

Parasite drag reduction evaluation is composed of wind tunnel tests with a standard L-1011 tail and two reduced area tail configurations. Trim drag reduction is evaluated by rebalancing the airplane for relaxed static stability. This is accomplished by pumping water to tanks in the forward and aft of the airplane to acheive desired center of gravity location. Also, the L-1011 is modified to incorporate term and advanced augmented systems. By using advanced wings and aircraft relaxed static stability significant fuel savings can be realized. An airplane's dynamic stability becomes more sensitive for decreased tail size, relaxed static stability, and advanced wing configurations. Active control pitch augmentation will be used to acheive the required handling qualities. Flight tests will be performed to evaluate the pitch augmentation systems. The effect of elevator downrig on stabilizer/elevator hinge moments will be measured. For control system analysis, the normal acceleration feedback and pitch rate feedback are analyzed.

Source record↗

NASA NTRS2000

Enhancement of Directional Ambiguity Removal Skill in Scatterometer Data Processing Using Planetary Boundary Layer Models

Planetary boundary layer (PBL) models are utilized to enhance directional ambiguity removal skill in scatterometer data processing. The ambiguity in wind direction retrieved from scatterometer measurements is removed with the aid of physical directional information obtained from PBL models. This technique is based on the observation that sea level pressure is scalar and its field is more coherent than the corresponding wind. An initial wind field obtained from the scatterometer measurements is used to derive a pressure field with a PBL model. After filtering small-scale noise in the derived pressure field, a wind field is generated with an inverted PBL model. This derived wind information is then used to remove wind vector ambiguities in the scatterometer data. It is found that the ambiguity removal skill can be improved when the new technique is used properly in conjunction with the median filter being used for scatterometer wind dealiasing at JPL. The new technique is applied to regions of cyclone systems which are important for accurate weather prediction but where the errors of ambiguity removal are often large.

Kim, Young-Joon↗

NASA NTRS2010

Mercury's Dynamic Magnetic Tail

The Mariner 10 and MESSENGER flybys of Mercury have revealed a magnetosphere that is likely the most responsive to upstream interplanetary conditions of any in the solar system. The source of the great dynamic variability observed during these brief passages is due to Mercury's proximity to the Sun and the inverse proportionality between reconnection rate and solar wind Alfven Mach number. However, this planet's lack of an ionosphere and its small physical dimensions also contribute to Mercury's very brief Dungey cycle, approx. 2 min, which governs the time scale for internal plasma circulation. Current observations and understanding of the structure and dynamics of Mercury's magnetotail are summarized and discussed. Special emphasis will be placed upon such questions as: 1) How much access does the solar wind have to this small magnetosphere as a function of upstream conditions? 2) What roles do heavy planetary ions play? 3) Do Earth-like substorms take place at Mercury? 4) How does Mercury's tail respond to extreme solar wind events such coronal mass ejections? Prospects for progress due to advances in the global magnetohydrodynamic and hybrid simulation modeling and the measurements to be taken by MESSENGER after it enters Mercury orbit on March 18, 2011 will be discussed.

Slavin, James A.↗

NASA NTRS2008

Proceedings of the 39th Lunar and Planetary Science Conference

Sessions with oral presentations include: A SPECIAL SESSION: MESSENGER at Mercury, Mars: Pingos, Polygons, and Other Puzzles, Solar Wind and Genesis: Measurements and Interpretation, Asteroids, Comets, and Small Bodies, Mars: Ice On the Ground and In the Ground, SPECIAL SESSION: Results from Kaguya (SELENE) Mission to the Moon, Outer Planet Satellites: Not Titan, Not Enceladus, SPECIAL SESSION: Lunar Science: Past, Present, and Future, Mars: North Pole, South Pole - Structure and Evolution, Refractory Inclusions, Impact Events: Modeling, Experiments, and Observations, Mars Sedimentary Processes from Victoria Crater to the Columbia Hills, Formation and Alteration of Carbonaceous Chondrites, New Achondrite GRA 06128/GRA 06129 - Origins Unknown, The Science Behind Lunar Missions, Mars Volcanics and Tectonics, From Dust to Planets (Planetary Formation and Planetesimals):When, Where, and Kaboom! Astrobiology: Biosignatures, Impacts, Habitability, Excavating a Comet, Mars Interior Dynamics to Exterior Impacts, Achondrites, Lunar Remote Sensing, Mars Aeolian Processes and Gully Formation Mechanisms, Solar Nebula Shake and Bake: Mixing and Isotopes, Lunar Geophysics, Meteorites from Mars: Shergottite and Nakhlite Invasion, Mars Fluvial Geomorphology, Chondrules and Chondrule Formation, Lunar Samples: Chronology, Geochemistry, and Petrology, Enceladus, Venus: Resurfacing and Topography (with Pancakes!), Overview of the Lunar Reconnaissance Orbiter Mission, Mars Sulfates, Phyllosilicates, and Their Aqueous Sources, Ordinary and Enstatite Chondrites, Impact Calibration and Effects, Comparative Planetology, Analogs: Environments and Materials, Mars: The Orbital View of Sediments and Aqueous Mineralogy, Planetary Differentiation, Titan, Presolar Grains: Still More Isotopes Out of This World, Poster sessions include: Education and Public Outreach Programs, Early Solar System and Planet Formation, Solar Wind and Genesis, Asteroids, Comets, and Small Bodies, Carbonaceous Chondrites, Chondrules and Chondrule Formation, Chondrites, Refractory Inclusions, Organics in Chondrites, Meteorites: Techniques, Experiments, and Physical Properties, MESSENGER and Mercury, Lunar Science Present: Kaguya (SELENE) Results, Lunar Remote Sensing: Basins and Mapping of Geology and Geochemistry, Lunar Science: Dust and Ice, Lunar Science: Missions and Planning, Mars: Layered, Icy, and Polygonal, Mars Stratigraphy and Sedimentology, Mars (Peri)Glacial, Mars Polar (and Vast), Mars, You are Here: Landing Sites and Imagery, Mars Volcanics and Magmas, Mars Atmosphere, Impact Events: Modeling, Experiments, and Observation, Ice is Nice: Mostly Outer Planet Satellites, Galilean Satellites, The Big Giant Planets, Astrobiology, In Situ Instrumentation, Rocket Scientist's Toolbox: Mission Science and Operations, Spacecraft Missions, Presolar Grains, Micrometeorites, Condensation-Evaporation: Stardust Ties, Comet Dust, Comparative Planetology, Planetary Differentiation, Lunar Meteorites, Nonchondritic Meteorites, Martian Meteorites, Apollo Samples and Lunar Interior, Lunar Geophysics, Lunar Science: Geophysics, Surface Science, and Extralunar Components, Mars, Remotely, Mars Orbital Data - Methods and Interpretation, Mars Tectonics and Dynamics, Mars Craters: Tiny to Humongous, Mars Sedimentary Mineralogy, Martian Gullies and Slope Streaks, Mars Fluvial Geomorphology, Mars Aeolian Processes, Mars Data and Mission,s Venus Mapping, Modeling, and Data Analysis, Titan, Icy Dwarf Satellites, Rocket Scientist's Toolbox: In Situ Analysis, Remote Sensing Approaches, Advances, and Applications, Analogs: Sulfates - Earth and Lab to Mars, Analogs: Remote Sensing and Spectroscopy, Analogs: Methods and Instruments, Analogs: Weird Places!. Print Only Early Solar System, Solar Wind, IDPs, Presolar/Solar Grains, Stardust, Comets, Asteroids, and Phobos, Venus, Mercury, Moon, Meteorites, Mars, Astrobiology, Impacts, Outer Planets, Satellites, and Rings, Support for Mission Operations, Analog Education and Public Outreach.

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NASA NTRS2009

MHD Modeling of the Solar Wind with Turbulence Transport and Heating

We have developed a magnetohydrodynamic model that describes the global axisymmetric steady-state structure of the solar wind near solar minimum with account for transport of small-scale turbulence associated heating. The Reynolds-averaged mass, momentum, induction, and energy equations for the large-scale solar wind flow are solved simultaneously with the turbulence transport equations in the region from 0.3 to 100 AU. The large-scale equations include subgrid-scale terms due to turbulence and the turbulence (small-scale) equations describe the effects of transport and (phenomenologically) dissipation of the MHD turbulence based on a few statistical parameters (turbulence energy, normalized cross-helicity, and correlation scale). The coupled set of equations is integrated numerically for a source dipole field on the Sun by a time-relaxation method in the corotating frame of reference. We present results on the plasma, magnetic field, and turbulence distributions throughout the heliosphere and on the role of the turbulence in the large-scale structure and temperature distribution in the solar wind.

Goldstein, M. L.↗

NASA NTRS1989

The acoustics of a small-scale helicopter rotor in hover

A 2.1 m diameter, 1/6-scale model helicopter main rotor was tested in hover in the test section of the NASA Ames 40- by 80-foot wind tunnel. Performance and noise data on a small-scale rotor at various thrust coefficients and tip Mach numbers were obtained for comparison with existing data on similar full-scale helicopter rotors. These data form part of a data base to permit the estimation of scaling effects on various rotor noise mechanisms. Another objective was to contribute to a data base that will permit the estimation of facility effects on acoustic testing. Acoustic 1/3-octave-band spectra are presented, together with variations of overall acoustic levels with rotor performance, microphone distance, and directivity angle.

Kitaplioglu, Cahit↗

NASA NTRS1975

An impact analysis of a micro wind system

A process for the recovery of steel mill stack dust has been developed and is being used to recover secondary metals by a small company in Georgia. The process is energy intensive and wind generators were studied as a means of supplying energy for part of the recovery process. Some of the results of this study will be presented.

Zimmer, R. P.↗

NASA NTRS1986

Instabilities in line-driven stellar winds. III - Wave propagation in the case of pure line absorption

The spatial and temporal evolution of small-amplitude velocity perturbations is examined in the idealized case of a stellar wind that is driven by pure line absorption of the star's continuum radiation. It is established that the instability in the supersonic region is of the advective type relative to the star, but of the absolute type relative to the wind itself. It is also shown that the inward propagation of information in such a wind is limited to the sound speed, in contrast to the theory of Abbott, which predicts inward propagation faster than sound. This apparent contradiction is resolved through an extensive discussion of the analytically soluble case of zero sound speed.

Owocki, S. P.↗

NASA NTRS1995

Elemental and charge state composition of the fast solar wind observed with SMS instruments on WIND

The elemental composition and charge state distributions of heavy ions of the solar wind provide essential information about: (1) atom-ion separation processes in the solar atmosphere leading to the 'FIP effect' (the overabundance of low First Ionization potential (FIP) elements in the solar wind compared to the photosphere); and (2) coronal temperature profiles, as well as mechanisms which heat the corona and accelerate the solar wind. This information is required for solar wind acceleration models. The SWICS instrument on Ulysses measures for all solar wind flow conditions the relative abundance of about 8 elements and 20 charge states of the solar wind. Furthermore, the Ulysses high-latitude orbit provides an unprecedented look at the solar wind from the polar coronal holes near solar minimum conditions. The MASS instrument on the WIND spacecraft is a high-mass resolution solar wind ion mass spectrometer that will provide routinely not only the abundances and charge state of all elements easily measured with SWICS, but also of N, Mg, S. The MASS sensor was fully operational at the end of 1994 and has sampled the in-ecliptic solar wind composition in both the slow and the corotating fast streams. This unique combination of SWICS on Ulysses and MASS on WIND allows us to view for the first time the solar wind from two regions of the large coronal hole. Observations with SWICS in the coronal hole wind: (1) indicate that the FIP effect is small; and (2) allow us determine the altitude of the maximum in the electron temperature profile, and indicate a maximum temperature of approximately 1.5 MK. New results from the SMS instruments on Wind will be compared with results from SWICS on Ulysses.

Gloeckler, G.↗

NASA NTRS1983

Dynamical evolution of interplanetary magnetic fields and flows between 0.3 AU and 8.5 AU - Entrainment

An analysis is presented of the radial evolution of interplanetary flows and associated magnetic fields between 0.3 AU and 8.5 AU using data from Helios 1 and B Voyager 1, respectively. The results indicate that in moving to 8 AU the largest corotating streams swept up the slower flows and shocks into a relatively thin region in which they coalesced to form a single large-amplitude compression. As a result of this process, referred to as entrainment, memory of the sources and flow configurations near the sun is lost, while small-scale features are erased as the flows move outward and energy is transferred from small scales to large scales.It is concluded that in the outer solar system the structure of the solar wind may be dominated by large scale pressure waves separated by several AU, while beyond several AU most of the compression waves are no longer driven by streams, and the compression waves expand freely. At large distances (greater than 25 AU) these compression waves will have interacted extensively with one another producing another state of the solar wind, with fewer large-scale nonuniformities and more small-scale nonuniformities.

Burlaga, L. F.↗

NASA NTRS2009

Transition Analysis for the Mars Science Laboratory Entry Vehicle

Viscous Laminar-turbulent transition plays an important role in the design of the Mars Science Laboratory (MSL) entry vehicle. The lift-to-drag ratio required for the precision landing trajectory will be achieved via an angle of attack equal to 16 degrees. At this relatively high angle of attack, the boundary layer flow near the leeward meridian is expected to transition early in the trajectory, resulting in substantially increased heating loads. This paper presents stability calculations and transition correlations for a series of wind tunnel models of the MSL vehicle. Experimentally measured transition onset locations are used to correlate with the N-factor calculations for various wind tunnel conditions. Due to relatively low post-shock Mach numbers near the edge of the boundary layer, the dominant instability waves are found to be of the first mode type. The N-factor values correlating with measured transition onset at selected test points from the Mach 6 conventional facility experiments fall between 3.5 and 4.5 and apparently vary linearly with the wind tunnel unit Reynolds number, indicating strong receptivity effect. The small transition N value is consistent with previous correlations for second-mode dominant transition in the same wind tunnel facility. Stability calculations for stationary and traveling crossflow instability waves in selected configurations indicate that an N value of 4 and 6, respectively, correlates reasonably well with transition onset discerned from one experimentally measured thermographic image.

Chang, Chau-Lyan↗

NASA NTRS1991

Discovery of a Doppler-limited CO line in the upper mesosphere of Venus - A new dynamical probe

The presence of CO in the upper atmosphere of Venus is a consequence of the photochemistry of CO2, the dominant atmospheric constituent. In December 1989 the J = 1-2 transition of CO was observed at 230 GHz. In addition to the broad absorption line first reported by Kakar et al. (1976), a narrow absorption feature at the center of the line due to upper mesospheric CO, where the temperature profile starts to exhibit diurnal variation with altitude. The narrow feature is approximately 600 kHz wide and is predominantly Doppler-broadened. The Doppler core provides a new means of measuring wind velocities at these altitudes in the atmosphere of Venus. Detection of small Doppler shifts in the line core can in principle be used to measure winds with an accuracy of 10 m/s. Results are presently limited by the 17 kHz uncertainty in the measured rest frequency, corresponding to a systematic error in wind velocity up to 22 m/s, and the absence of laboratory measurements of the pressure shift in CO by CO2.

Buhl, David↗

NASA NTRS1988

Expectations for the microphysics of the Mars-solar wind interaction

The two Phobos spacecraft, which will start to orbit Mars early in 1989, will be capable of investigating in detail the microphysics of the Mars-solar wind interaction. Simple scaling arguments and analogies with other planetary bow shocks indicate that the sub-solar shock standoff distance should be small compared with plasma scalelengths, giving the shocked solar wind insufficient space in which to thermalize downstream before encountering the magnetospheric obstacle. Both the magnetosphere and ionosphere can be affected by particles and waves from the solar wind interaction.

Moses, S. L.↗

NASA NTRS2020

Recent NASA Wind Tunnel Free-Flight Testing of a Multirotor Unmanned Aircraft System Vehicle

Wind tunnel free-flight tests of a small quadrotor vehicle were completed in the NASA Langley 12-Foot Low Speed Tunnel and 20-Foot Vertical Spin Tunnel. The primary objective of these tests was to acquire flight data in forward and descending flight for the purpose of assessing the fidelity of an all-attitude flight dynamics simulation previously developed from static and dynamic wind tunnel data. A secondary objective was to demonstrate and mature free-flight test methods specific to the emerging class of small unmanned aircraft and urban air mobility vehicles. Experimental flight data correlated well with simulation predictions which included steady trim conditions consistent with straight and level flight and quasi-steady conditions associated with descent velocities prone to vortex ring state development. The test method was shown to be well suited to these classes of vehicles and several unique infrastructure requirements, including tether systems and data acquisition requirements were identified. In addition, unique operational test techniques and safety procedures were developed to accommodate the testing. Results of these tests will be used to support air traffic management studies and research into safety assurance concepts that enable the integration of these classes of vehicles into the National Airspace System.

John V Foster↗

NASA NTRS2004

Transition from Forward Smoldering to Flaming in Small Polyurethane Foam Samples

Experimental observations are presented of the effect of the flow velocity and oxygen concentration, and of a thermal radiant flux, on the transition from smoldering to flaming in forward smoldering of small samples of polyurethane foam with a gas/solid interface. The experiments are part of a project studying the transition from smolder to flaming under conditions encountered in spacecraft facilities, i.e., microgravity, low velocity variable oxygen concentration flows. Because the microgravity experiments are planned for the International Space Station, the foam samples had to be limited in size for safety and launch mass reasons. The feasible sample size is too small for smolder to self propagate because of heat losses to the surrounding environment. Thus, the smolder propagation and the transition to flaming had to be assisted by reducing the heat losses to the surroundings and increasing the oxygen concentration. The experiments are conducted with small parallelepiped samples vertically placed in a wind tunnel. Three of the sample lateral-sides are maintained at elevated temperature and the fourth side is exposed to an upward flow and to a radiant flux. It is found that decreasing the flow velocity and increasing its oxygen concentration, and/or increasing the radiant flux enhances the transition to flaming, and reduces the delay time to transition. Limiting external ambient conditions for the transition to flaming are reported for the present experimental set-up. The results show that smolder propagation and the transition to flaming can occur in relatively small fuel samples if the external conditions are appropriate. The results also indicate that transition to flaming occurs in the char left behind by the smolder reaction, and it has the characteristics of a gas-phase ignition induced by the smolder reaction, which acts as the source of both gaseous fuel and heat.

Bar-Ilan, A.↗