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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 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Low-profile heliostat design for solar central receiver systems

Heliostat designs intended to reduce costs and the effect of adverse wind loads on the devices were developed. Included was the low-profile heliostat consisting of a stiff frame with sectional focusing reflectors coupled together to turn as a unit. The entire frame is arranged to turn angularly about a center point. The ability of the heliostat to rotate about both the vertical and horizontal axes permits a central computer control system to continuously aim the sun's reflection onto a selected target. An engineering model of the basic device was built and is being tested. Control and mirror parameters, such as roughness and need for fine aiming, are being studied. The fabrication of these prototypes is in process. The model was also designed to test mirror focusing techniques, heliostat geometry, mechanical functioning, and tracking control. The model can be easily relocated to test mirror imaging on a tower from various directions. In addition to steering and aiming studies, the tests include the effects of temperature changes, wind gusting and weathering. The results of economic studies on this heliostat are also presented.

Fourakis, E.↗
NASA NTRS1987

Steady state flow/field model of solar wind interaction with Venus - Global implications of local effects

Physical and chemical processes in the Venus ionosphere driven by the interaction of the solar wind with the atmosphere of Venus are described, and a model describing the interrelationships of these processes in a self-consistent manner is formulated. It is shown that the magnetic field configuration of the ionosphere is a steady state global structure which results from a combination of a large-scale 'open' current system connecting through the ionopause to the postshock solar wind and two small-scale 'closed' current systems entirely confined within the ionosphere and generated by ionospheric flows and shears. A previously detected ionospheric layer in O2(+) near 170 km altitude is shown to be a new type of ionospheric layer resulting from transition of solar-wind-driven vertical flow to velocities approaching Mach 1.

Cloutier, P. A.↗
NASA NTRS1988

Simulation of fundamental atomization mechanisms in fuel sprays

Growth of instabilities on the liquid/gas interface in the initial region of fuel sprays is studied by means of numerical simulations. The simulations are based on solutions of the variable-density incompressible Navier-Stokes equations, which are obtained with a new numerical algorithm. The simulations give good agreement with analytical results for the instabilities on a liquid cylinder induced by surface tension and wind-induced instabilities. The effects of boundary layers on the wind-induced instabilities are investigated. It is found that a boundary layer reduces the growth rate for a single interface, and a comparison with inviscid theory suggests that boundary layer effects may be significantly more important than surface tension effects. The results yield a better estimate than inviscid theory for the drop sizes as reported for diesel sprays. Results for the planar jet show that boundary layer effects hasten the growth of Squire's 'symmetric' mode, which is responsible for jet disintegration. This result helps explain the rapid atomization which occurs in swirl and air-blast atomizers.

Childs, Robert, E.↗
NASA NTRS1999

Aerothermodynamic Calculations on X-34 at Mach 6 Wind Tunnel Conditions

The effects of Reynolds number and turbulence on surface heat-transfer rates are numerically investigated for a 0.015 scale X-34 vehicle at wind tunnel conditions. Laminar heating rates, non-dimensionalized by Fay-Riddell stagnation heating, do not change appreciably with an order of magnitude variation in Reynolds number. Modeling a turbulent versus laminar boundary layer at the same Reynolds number increases the windside heating by a factor of four, portions on the leeside by a factor of two, and causes a 30 percent increase in wing leading edge heating. A discrepancy between laminar and turbulent heating trends on the windside centerline is explained by the presence of attached windside vortices in the laminar solutions, structures that are inhibited by the turbulence modeling.

Wood, William A.↗
DOE OSTI2017

Impacts of interactive dust and its direct radiative forcing on interannual variations of temperature and precipitation in winter over East Asia

In this work, we used 150-year pre-industrial simulations of the Community Earth System Model (CESM) to quantify the impacts of interactively-modeled dust emissions on the interannual variations of temperature and precipitation over East Asia during the East Asian Winter Monsoon (EAWM) season. The simulated December-January-February dust column burden and dust optical depth are lower over northern China in the strongest EAWM years than those of the weakest years, with regional mean values lower by 38.3% and 37.2%, respectively. The decrease in dust over the dust source regions (the Taklamakan and Gobi Deserts) and the downwind region (such as the North China Plain) leads to an increase in direct radiative forcing (RF) both at the surface and top of atmosphere by up to 1.5 and 0.75 W m-2, respectively. The effects of EAWM-related variations in surface winds, precipitation and their effects on dust emissions and wet removal contribute about 67% to the total dust-induced variations of direct RF at the surface and partly offset the cooling that occurs with the EAWM strengthening by heating the surface. The variations of surface air temperature induced by the changes in wind and dust emissions increase by 0.4-0.6 K over eastern coastal China, northeastern China, and Japan, which weakens the impact of EAWM on surface air temperature by 3–18% in these regions. The warming results from the combined effects of changes in direct RF and easterly wind anomalies that bring warm air from the ocean to these regions. Moreover, the feedback of the changes in wind on dust emissions weakens the variations of the sea level pressure gradient on the Siberian High while enhancing the Maritime Continent Low. Therefore, cold air is prevented from being transported from Siberia, Kazakhstan, western and central China to the western Pacific Ocean and decreases surface air temperature by 0.6 K and 2 K over central China and the Tibetan Plateau, respectively. Over eastern coastal China, the variations of large-scale precipitation induced by the feedback of EAWM-related changes in wind on dust emissions increase by 10-30% in winter because of the increase in surface air temperature and the anomalous circulation.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2002

An XMM Investigation of Non-Thermal Phenomena in the Winds of Early-Type Stars

The X-ray emission from early-type stars is believed to arise from a stellar wind distribution of shocks. Hence, X-ray analyses of these stars must include the effects of stellar wind X-ray absorption, which, in general dominates the ISM absorption. Although the absorption cross sections for the wind and ISM are essentially identical above 1 keV, there is substantial differences below 1 keV. Typically, if one only uses ISM cross sections to obtain fits to X-ray spectra, the fits usually indicate a model deficiency at energies below 1 keV which is attributed to the large increase in ISM cross sections at these energies. This deficiency can be eliminated by using stellar wind absorption models with a fixed ISM component. Since all early-type stars have substantial X-ray emission below 1 keV, than inclusion of wind absorption has proven to be a critical component in fitting X-ray spectra at low energies, verifying that these X-rays are indeed arising from within the stellar wind.

Waldron, Wayne L.↗
DOE OSTI2013

DEVIATION OF STELLAR ORBITS FROM TEST PARTICLE TRAJECTORIES AROUND SGr A* DUE TO TIDES AND WINDS

Monitoring the orbits of stars around Sgr A* offers the possibility of detecting the precession of their orbital planes due to frame dragging, of measuring the spin and quadrupole moment of the black hole, and of testing the no-hair theorem. Here we investigate whether the deviations of stellar orbits from test-particle trajectories due to wind mass loss and tidal dissipation of the orbital energy compromise such measurements. We find that the effects of stellar winds are, in general, negligible. On the other hand, for the most eccentric orbits (e > 0.96) for which an optical interferometer, such as GRAVITY, will detect orbital plane precession due to frame dragging, the tidal dissipation of orbital energy occurs at timescales comparable to the timescale of precession due to the quadrupole moment of the black hole. As a result, this non-conservative effect is a potential source of systematic uncertainty in testing the no-hair theorem with stellar orbits.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2014

Solar Wind Sputtering of Lunar Soil Analogs: The Effect of Ionic Charge and Mass

In this contribution we report sput-tering measurements of anorthite, an analog material representative of the lunar highlands, by singly and multicharged ions representative of the solar wind. The ions investigated include protons, as well as singly and multicharged Ar ions (as proxies for the heavier solar wind constituents), in the charge state range +1 to +9, and had a fixed solar-wind-relevant impact velocity of approximately 310 km/s or 500 eV/ amu. The goal of the measurements was to determine the sputtering contribution of the heavy, multicharged minority solar wind constituents in comparison to that due to the dominant H+ fraction.

Hijazi, H.↗
NASA NTRS1975

Results of tests of a Rockwell International space shuttle orbiter (-139 configuration) 0.0175-scale model (no. 29-0) in AEDC tunnel F to determine hypersonic heating effects (OH11)

Results from wind tunnel tests to determine hypersonic aerodynamic heating rates on a NASA/Rockwell Space Shuttle Orbiter are reported. The tests were to determine Mach number effects, if any, and to obtain overall heating rate data at high Mach numbers from 10.5 to 16. The model used was a 0.0175-scale model built to Rockwell Orbiter lines VL70-000139. The model identity number is 29-0. These tests, designated OH11, were conducted in the AEDC Tunnel F.

Quan, M.↗
NASA NTRS1978

Investigation of aircraft landing in variable wind fields

A digital simulation study is reported of the effects of gusts and wind shear on the approach and landing of aircraft. The gusts and wind shear are primarily those associated with wind fields created by surface wind passing around bluff geometries characteristic of buildings. Also, flight through a simple model of a thunderstorm is investigated. A two-dimensional model of aircraft motion was represented by a set of nonlinear equations which accounted for both spatial and temporal variations of winds. The landings of aircraft with the characteristics of a DC-8 and a DHC-6 were digitally simulated under different wind conditions with fixed and automatic controls. The resulting deviations in touchdown points and the controls that are required to maintain the desired flight path are presented. The presence of large bluff objects, such as buildings in the flight path is shown to have considerable effect on aircraft landings.

Frost, W.↗
NASA NTRS1998

Signal Analysis of Helicopter Blade-Vortex-Interaction Acoustic Noise Data

Blade-Vortex-Interaction (BVI) produces annoying high-intensity impulsive noise. NASA Ames collected several sets of BVI noise data during in-flight and wind tunnel tests. The goal of this work is to extract the essential features of the BVI signals from the in-flight data and examine the feasibility of extracting those features from BVI noise recorded inside a large wind tunnel. BVI noise generating mechanisms and BVI radiation patterns an are considered and a simple mathematical-physical model is presented. It allows the construction of simple synthetic BVI events that are comparable to free flight data. The boundary effects of the wind tunnel floor and ceiling are identified and more complex synthetic BVI events are constructed to account for features observed in the wind tunnel data. It is demonstrated that improved recording of BVI events can be attained by changing the geometry of the rotor hub, floor, ceiling and microphone. The Euclidean distance measure is used to align BVI events from each blade and improved BVI signals are obtained by time-domain averaging the aligned data. The differences between BVI events for individual blades are then apparent. Removal of wind tunnel background noise by optimal Wiener-filtering is shown to be effective provided representative noise-only data have been recorded. Elimination of wind tunnel reflections by cepstral and optimal filtering deconvolution is examined. It is seen that the cepstral method is not applicable but that a pragmatic optimal filtering approach gives encouraging results. Recommendations for further work include: altering measurement geometry, real-time data observation and evaluation, examining reflection signals (particularly those from the ceiling) and performing further analysis of expected BVI signals for flight conditions of interest so that microphone placement can be optimized for each condition.

Rogers, James C.↗
DOE OSTI2016

Multivariate Predictive Analytics of Wind Power Data for Robust Control of Energy Storage

Short-term forecasting is frequently identified as an important tool for the effective management of wind generation. However, forecasting errors, inherent to the point forecasts, increase requirements for energy storage and can affect optimal system operation. Probabilistic forecasts can help tackle this issue by providing a proper characterization of forecasting errors in the optimization process. This paper proposes a multivariate model of forecasting data for wind generation. Predictive uncertainty intervals of wind power can be obtained by sampling from the proposed model. The main goal is to use empirical data models without linear or Gaussian approximations of the distributional or temporal variations. The predictive modeling is utilized within a case study of an energy storage system. Finally, a modified robust convex programming is used to maintain the practical robustness and feasibility of the solution based on the sampled scenarios from the model.

17 WIND ENERGY↗
NASA NTRS1974

Reynolds number effects on boattail drag of exhaust nozzles from wind tunnel and flight tests

A family of nacelle-mounted high-angle boattail nozzles was tested to investigate Reynolds number effects on drag. The nozzles were flown on a modified F-106B and mounted on scale models of an F-106 in a wind tunnel. A 19-to-1 range of Reynolds number was covered as a result of the large size differences between models and by flying over a range of altitude. In flight the nozzles were mounted behind J-85 turbojet engines. Jet boundary simulators and a powered turbojet engine simulator were used on the wind tunnel models. Data were taken at Mach numbers of 0.6 and 0.9. Boattail drag was found to be affected by Reynolds number. The effect is a complex relationship dependent upon boundary layer thickness and nozzle boattail shape. As Reynolds number was increased from the lowest values obtained with scale models, boattail drag first increased to a maximum at the lowest flight Reynolds number and then decreased.

Wilcox, F. A.↗
NASA NTRS1994

The effect of wave-particle interactions on the polar wind: Preliminary results

A Monte Carlo simulation was developed in order to study the effects of wave-particle interactions (WPI) on the plasma outflow in the polar wind. The simulation also considered the other mechanisms included in the `classical' polar wind studies such as gravity, the polarization electrostatic field, and the divergence of geomagnetic field lines. Although the plasma consisted of electrons, H(+) and O(+) ions, we emphasized the behavior of H(+) in this preliminary study. The ion distribution function, as well as the profiles of its moments (density, drift velocity, temperatures, etc.) were found for different levels of WPI, that is, for different values of normalized diffusion rates in the velocity space (normalized D(sub perpendicular) H(+)). We found that as the WPI strength increases: (1) the ion drift velocity increases and its density decreases; (2) the perpendicular temperature T(sub perpendicular) (H(+)) increases; (3) the parallel temperature T(sub parallel) (H(+)) first decreases and then increases due to the balance between the parallel adiabatic cooling and the transfer of the energy from the perpendicular to the parallel direction; and (4) the temperature anisotropy ((T(sub parallel) (H(+))/T(sub perpendicular) (H(+)) is reduced and even reversed in some cases. For strong WPI (normalized D(sub perpendicular) (H(+) much greater than 1), the ion distribution function shows weak conic features at high altitudes.

Barakat, A. R.↗
DOE OSTI2014

Effects of Second-Order Hydrodynamic Forces on Floating Offshore Wind Turbines

Relative to first-order, second-order wave-excitation loads are known to cause significant motions and additional loads in offshore oil and gas platforms. The design of floating offshore wind turbines was partially inherited from the offshore oil and gas industry. Floating offshore wind concepts have been studied with powerful aero-hydro-servo-elastic tools; however, most of the existing work on floating offshore wind turbines has neglected the contribution of second-order wave-excitation loads. As a result, this paper presents a computationally efficient methodology to consider these loads within FAST, a wind turbine computer-aided engineering tool developed by the National Renewable Energy Laboratory. The method implemented was verified against the commercial OrcaFlex tool, with good agreement, and low computational time. A reference floating offshore wind turbine was studied under several wind and wave load conditions, including the effects of second-order slow-drift and sum-frequency loads. Preliminary results revealed that these loads excite the turbine's natural frequencies, namely the surge and pitch natural frequencies.

13 HYDRO ENERGY↗
NASA NTRS1983

Effect of boundary layers on solid walls in three-dimensional subsonic wind tunnels

A linear method is developed which accounts for the effects of boundary layers on solid walls in subsonic three-dimensional wind tunnels. The streamwise gradient of the displacement thickness for a solid-wall boundary layer is expressed in terms of the von Karman momentum integral. The growth of the boundary layer due to the wall shearing stress is small compared to the variation caused by the model-induced pressure gradient. The viscous boundary condition can be expressed in terms of the edge velocity gradient and the gradient of the inviscid velocity potential function at the wall. Utilizing this analysis on the solid walls of several three-dimensional wind tunnel configurations shows that the most pronounced wall boundary-layer effect is on solid blockage for completely closed wind tunnels. For solid-wall tunnel configurations, the streamline curvature interference factor is reduced by a significant amount, while the lift interference factor at the model station does not depend on the boundary-layer parameter. For combination wall configurations, the slot effect of the horizontal walls dominates the viscous effect of the solid sidewalls.

Adcock, J. B.↗
NASA NTRS1976

Investigation of some effects of humidity on aerodynamic characteristics on a 10-percent-thick NASA supercritical airfoil

An investigation was conducted in the Langley 8-foot transonic pressure tunnel to determine the effects of wind-tunnel humidity on the aerodynamic characteristics of a 10-percent-thick NASA supercritical airfoil. Effects of dewpoint variation from 267 K (20 F) to 294 K (70 F) were investigated. The tunnel stagnation temperature was 322 K (120 F) and the stagnation pressure was 0.1013 MN/09 m (1 atm).

Jordan, F. L., Jr.↗
NASA NTRS1984

Reel Down - A balloon borne winch system for stratospheric sounding from above

A balloon-borne winch system has been developed and flight tested which permits the repetitive lowering and hoisting of a stratospheric sampling payload for distances of up to 20 km from a float altitude of 35-40 km. This new approach to in situ stratospheric measurements permits multiple scans of various depths and velocities, closely spaced over a period of hours or days, thus dramatically increasing observational effectiveness. The motor driven winch permits control of ascent velocities from 0-9 m/s with energy derived from a large battery; for descent, the motors are used as generators, velocity is controlled over the same range, and the energy is dumped radiatively to space. The 1.75 mm diameter tether is of braided Kevlar construction with a nylon jacket; it exhibits a 2900 N break strength. Both the winch and the payload suspended by the tether are fully instrumented to evaluate potentially destructive system-induced dynamics and the effects of stratospheric wind shears. The system was successfully flight tested by lowering a 62 kg payload for a distance of 12 km from a float altitude of 38.5 km and hoisting it back up again, both at velocities ranging between 5-9 m/s. Observations indicated minimal system-induced dynamical effects, and no adverse effects due to the 8 m/s wind shear present during flight.

Hazen, N. L.↗