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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 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Calculations of transonic flow about an airfoil in a wind tunnel

A combined experimental and numerical study was performed to include wind-tunnel wall interference effects in calculations for airfoil flows at transonic speeds. Pressure-survey-tube and laser-Doppler velocimeter measurements were made in the flow field about an airfoil in the 2- by 2-Foot Transonic Wind Tunnel at Ames Research Center. The results were then used as boundary data in a Navier-Stokes code modified by incorporating a pressure condition on the upper and lower computational boundaries. Comparison of calculated results and experimental data obtained from the surface of the airfoil indicates that the pressure-boundary condition is particularly effective in moving the shock to a position near that observed experimentally when the flow remains attached. For flows with large separation, shock position and viscous-layer properties are not well predicted, principally because of the inadequacies of the algebraic turbulence models employed with the method.

King, L. S.↗
DOE OSTI2015

Determining the band gap and mean kinetic energy of atoms from reflection electron energy loss spectra

Reflection electron energy loss spectra from some insulating materials (CaCO{sub 3}, Li{sub 2}CO{sub 3}, and SiO{sub 2}) taken at relatively high incoming electron energies (5–40 keV) are analyzed. Here, one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected to the mean kinetic energy of the atom in the material (Doppler broadening). The experimentally obtained mean kinetic energies of the O, C, Li, Ca, and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding, we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO{sub 2}, good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E − E{sub gap}){sup 1.5}. For CaCO{sub 3}, the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li{sub 2}CO{sub 3} (7.5 eV) is the first experimental estimate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1978

Application of microprocessors to spacecraft synthetic aperture radar processing

A ground-based digital synthetic aperture radar (SAR) processor capable of correlating images from raw spacecraft data at real-time rates is currently under development. The processor design requirements are particularly formidable due to (1) range migration effects resulting from planetary curvature and rotation, (2) antenna beam pointing errors, and (3) variation of the Doppler reference function with changing orbital parameters. Based upon the current effort, this paper describes a candidate real-time on-board SAR processing implementation approach that might evolve for future spacecraft applications. Key features include the use of custom large scale integration (LSI) charge-coupled device (CCD) technology to accomplish the correlation functions and microprocessor technology to effect control.

Arens, W. E.↗
NASA NTRS1988

Evidence for a common high-temperature superconducting effect in La(1.85)Sr(0.15)CuO4 and YBa2Cu3O7

The paper reports the positron-annihilation lifetime and Doppler-broadening energy spectra in La(1.85)Sr(0.15)CuO4 superconductors for T = 10-297 K. A strong temperature dependence in positron lifetime and momentum distribution parameters is observed for positron-electron annihilation data while the sample is in the superconducting state, but not while it is in the normal state. Experimental evidence is presented that the superconducting mechanisms in La(1.85)Sr(0.15)CuO4 and YBa2Cu3O7 are similar and it is suggested that this is a consequence of a common physics involving the delicate balance between localized- and itinerant-electron behavior.

Jean, Y. C.↗
NASA NTRS1993

SPNDL: A concept for a small satellite Doppler lidar wind sounder

Given current resources and the technical challenges in developing a full coverage space-based Doppler lidar wind measuring system such as LAWS (Laser Atmospheric Wind Sounder), it is not likely that the science community will have data streams with which to work before the end of this decade. Currently, a 'fast track' demonstration mission is being seriously considered by several U.S. agencies. Such a mission would have as its primary objectives the demonstration of coherent Doppler lidar technology in space and the delivery of wind observations for science algorithm evaluation and development. However, for such a mission to be achieved at modest costs and within a short time frame, deviations from the full system design are required. Simulation models have been developed over the last decade to aide in the design of Doppler lidar missions and to provide simulated data for use in wind computation algorithm development. SWA has used both models to examine some options that might be cost-effective for a demonstration mission. Over the past few months, Simpson Weather Associates has been studying SPNDL (Spinning Platform with a Non-rotating telescope Doppler Lidar), a new concept for Doppler lidar wind observations from space. Science and Technology Corporation has an interest in participating in an engineering and shuttle accommodation study for SPNDL.

Emmitt, G. D.↗
NASA NTRS1997

Upstream Swirl Effects on the Flow Inside a Labyrinth Seal

The flow field inside a seven cavity tooth on rotor labyrinth seal was measured using a 3D laser Doppler anemometer system. The seal was operated at a Reynolds number of 24,000 and a Taylor number of 6,600 using water as the working fluid. Swirl vanes were placed upstream of the seal to produce positive, negative, and no preswirl. It was found that the axial and radial velocities were minimally effected. The tangential velocity, both in the clearance region and the seal cavities on the rotor, were greatly altered by the preswirl. By applying negative preswirl, the tangential velocity was suppressed, even in the seventh cavity. The turbulence levels decreased as the preswirl varied from negative to positive.

Morrison, Gerald L.↗
NASA NTRS1995

Plane-wave analysis of solar acoustic-gravity waves: A (slightly) new approach

The plane-wave decomposition of the acoustic-gravity wave effects observed in the photosphere provides a computationally efficient technique that probes the structure of the upper convective zone and boundary. In this region, the flat sun approximation is considered as being reasonably accurate. A technique to be used for the systematic plane-wave analysis of Michelson Doppler imager data, as part of the solar oscillations investigation, is described. Estimates of sensitivity are presented, and the effects of using different planar mappings are discussed. The technique is compared with previous approaches to the three dimensional plane-wave problem.

Bogart, Richard S.↗
DOE OSTI2023

Evaluating wind profiles in a numerical weather prediction model with Doppler lidar

We use Doppler lidar wind profiles from six locations around the globe to evaluate the wind profile forecasts in the boundary layer generated by the operational global Integrated Forecast System (IFS) from the European Centre for Medium-range Weather Forecasts (ECMWF). The six locations selected cover a variety of surfaces with different characteristics (rural, marine, mountainous urban, and coastal urban). We first validated the Doppler lidar observations at four locations by comparison with co-located radiosonde profiles to ensure that the Doppler lidar observations were of sufficient quality. The two observation types agree well, with the mean absolute error (MAE) in wind speed almost always less than 1 m s –1 . Large deviations in the wind direction were usually only seen for low wind speeds and are due to the wind direction uncertainty increasing rapidly as the wind speed tends to zero. Time–height composites of the wind evaluation with 1 h resolution were generated, and evaluation of the model winds showed that the IFS model performs best over marine and coastal locations, where the mean absolute wind vector error was usually less than 3 m s –1 at all heights within the boundary layer. Larger errors were seen in locations where the surface was more complex, especially in the wind direction. For example, in Granada, which is near a high mountain range, the IFS model failed to capture a commonly occurring mountain breeze, which is highly dependent on the sub-grid-size terrain features that are not resolved by the model. The uncertainty in the wind forecasts increased with forecast lead time, but no increase in the bias was seen. At one location, we conditionally performed the wind evaluation based on the presence or absence of a low-level jet diagnosed from the Doppler lidar observations. The model was able to reproduce the presence of the low-level jet, but the wind speed maximum was about 2 m s –1 lower than observed. This is attributed to the effective vertical resolution of the model being too coarse to create the strong gradients in wind speed observed. Our results show that Doppler lidar is a suitable instrument for evaluating the boundary layer wind profiles in atmospheric models.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2016

Phased Array Beamforming and Imaging in Composite Laminates Using Guided Waves

This paper presents the phased array beamforming and imaging using guided waves in anisotropic composite laminates. A generic phased array beamforming formula is presented, based on the classic delay-and-sum principle. The generic formula considers direction-dependent guided wave properties induced by the anisotropic material properties of composites. Moreover, the array beamforming and imaging are performed in frequency domain where the guided wave dispersion effect has been considered. The presented phased array method is implemented with a non-contact scanning laser Doppler vibrometer (SLDV) to detect multiple defects at different locations in an anisotropic composite plate. The array is constructed of scan points in a small area rapidly scanned by the SLDV. Using the phased array method, multiple defects at different locations are successfully detected. Our study shows that the guided wave phased array method is a potential effective method for rapid inspection of large composite structures.

Tian, Zhenhua↗
NASA NTRS2018

Development of a Coherent Doppler Lidar for Precision Maneuvering and Landing of Space Vehicles

A coherent Doppler lidar has been developed to address NASA’s need for a high-performance, compact, and cost-effective velocity and altitude sensor onboard its landing vehicles. Future robotic and manned missions to planetary bodies require precise ground-relative velocity vector and altitude data to execute complex descent maneuvers and safe, soft landing at a pre-designated site. This lidar sensor, referred to as a Navigation Doppler Lidar, meets the required performance of landing missions while complying with vehicle size, mass, and power constraints. Operating from over five kilometers altitude, the lidar obtains velocity and range precision measurements with 2 cm/sec and 2 meters, respectively, dominated by the vehicle motion. After a series of flight tests onboard helicopters and rocket-powered free-flyer vehicles, the Navigation Doppler Lidar is now being ruggedized for future missions to various destinations in the solar system.

Amzaherdian, Farzin↗
NASA NTRS1975

Relativity mission with two counter-orbiting polar satellites

In 1918, J. Lense and H. Thirring calculated that a moon in orbit around a massive rotating planet would experience a nodal dragging effect due to general relativity. We describe an experiment to measure this effect with two counter-orbiting drag-free satellites in polar earth orbit. For a 2 1/2 year experiment, the measurement accuracy should approach 1%. In addition to precision tracking data from existing ground stations, satellite-to-satellite Doppler ranging data are taken at points of passing near the poles. New geophysical information on both earth harmonics and tidal effects is inherent in the polar ranging data.

Van Patten, R. A.↗
NASA NTRS1992

COBE anisotropy from supercluster gas

It is suggested that the microwave background anisotropy detected by the COBE DMR might be dominated not by the direct gravitational effect of primordial fluctuations in the last scattering surface, but by scattering off of moving electrons in optically thin, nearby superclusters. Hot diffuse clouds of ionized gas created during supercluster collapse produce Sunyaev-Zel'dovich and Doppler background anisotropy whose properties may closely mimic those of primordial anisotropy in current data. Strategies for and difficulties in separating the effects are discussed, based on the anisotropy spectrum, autocorrelation, correlation with galaxy catalogs, X-ray emission, and integrated spectral distortions.

Hogan, Craig J.↗
NASA NTRS1991

Doppler indices of gas phase formation in hypobaric environments: Time-intensity analysis

A semi-quantitative method to analyze decompression data is described. It possesses the advantage that it allows a graded response to decompression rather than the dichotomous response generally employed. A generalized critical volume (C-V), or stoichiometric time-dependent equilibrium model is examined that relates the constant of the equation P sub i equals m P sub f plus b to variable tissue supersaturation and gas washout terms. The effects of the tissue ratio on gas phase formation indicate that a decreased ratio yields fewer individuals with Doppler detectable gas bubbles, but those individuals still present with Spencer Grade 3 or 4. This might indicate a local collapse of tissue saturation. The individuals with Grade 3 or 4 could be at risk for type 2 decompression sickness by transpulmonic arterialization. The primary regulator of the problems of decompression sickness is the reduction of local supersaturation, presumably governed by the presence and number of gas micronuclei. It is postulated that a reduction in these nuclei will favor a low incidence of decompression sickness in microgravity secondary to hypokinesia and adynamia.

Powell, Michael R.↗
NASA NTRS1966

Pioneer project support

Pioneer project support - Doppler tracking data analysis, trajectory dispersions and initial tracking station acquisition, and gas leak effect on orbit

PIONEER SPACE PROBE↗
NASA NTRS1971

Lunar gravity derived from long-period satellite motion, a proposed method

A method was devised to determine the spherical harmonic coefficients of the lunar gravity field. The method consists of a two-step data reduction and estimation process. Pseudo-Doppler data were generated simulating two different lunar orbits. The analysis included the perturbing effects of the L1 lunar gravity field, the earth, the sun, and solar radiation pressure. Orbit determinations were performed on these data and long-period orbital elements were obtained. The Kepler element rates from these solutions were used to recover L1 lunar gravity coefficients. Overall results of the experiment show that lunar gravity coefficients can be accurately determined and that the method is dynamically consistent with long-period perturbation theory.

Ferrari, A. J.↗
NASA NTRS1972

Study of the Stark effect in the resonance lines of sodium by an atomic jet method

The reversal of the magnetic moment of a part of the atoms of a consecutive jet with optical excitation and on the return to the fundamental level is applied to the case of sodium, in order to complete previous results dealing with the alkalis. A conventional atomic jet apparatus consisting of two electromagnets with Rabi-type poles which produce magnetic field gradients of the same sense was used. The accuracy of measurement of the Stark effect by excitation of an atomic jet of high collimation is limited by the Doppler width of the lines emitted by the source or, if this width is diminished with the help of a connected process, by the luminous power available. The results make it possible to extend the experiments to the measurement of isotopic displacements of sodium.

Duong, H. T.↗
NASA NTRS1984

A review of ionospheric effects on Earth-space propagation

A short description is given of each ionospheric total electron content (TEC) effect upon radio waves, along with a representative value of the magnitude of each of these effects under normal ionospheric conditions. A discussion is given of the important characteristics of average ionospheric TEC behavior and the temporal and spatial variability of TEC. Radio waves undergo several effects when they pass through the Earth's ionosphere. One of the most important of these effects is a retardation, or group delay, on the modulation or information carried on the radio wave that is due to its encounter with the free, thermal electrons in the Earth's ionosphere. Other effects the ionosphere has on radio waves include: radio frequency (RF) carrier phase advance; Doppler shift of the RF carrier of the radio wave; Faraday rotation of the plane of polarization of linearly polarized waves; angular refraction or bending of the radio wave path as it travels through the ionosphere; and amplitude and phase scintillations.

Klobuchar, J. A.↗