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At least 127 records · Page 7

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NASA NTRS1999

Ice Flow in the Northeast Greenland Ice Stream

As the use of satellite data for icesheet research has accelerated, new discoveries have changed the way that we think about ice discharge, and new tools have changed the way that we measure it. We have begun to apply a combination of remote sensing and ice sheet modeling techniques to study ice flow in the recently identified northeast Greenland ice stream. This ice stream shows evidence of organized flow far into the interior and has low-slope areas of rapid flow and regions of enhanced shear that resemble the ice streams of West Antarctica. The onset of rapid flow close to the ice divide and the evolution of its flow pattern, however, make this ice stream unique. Our investigation is aimed at increasing our understanding of this ice stream and its origins and role in the discharge of ice from the ice sheet and the effects that discharge may have on the history and evolution of the ice in northern Greenland. The ice flow data comes from satellite radar interferometry tied to reference points. We have applied this technique to measure the velocity over the entire ice stream, which is more than 700 km in length. The velocity contours reveal distinct, well-developed shear margins, which are coincident with linear features in the Synthetic Aperture Radar (SAR) amplitude imagery. It is surprising to see such defined, enhanced flow so far inland and so close to the ice divide. The velocity data and topography data are being used to feed a modeling effort that allows us to study the dynamics and character rapid flow. Additional information is contained in the original.

Joughin, Ian↗

NASA NTRS2015

Fuselage-Induced Velocity Model for LRTA, RTA, and HART Fuselages

In order to make the aerodynamic fuselage-rotor interference effects available to comprehensive rotor codes, a simple analytical model of the fuselage-induced velocities within the volume of rotor blade operation above the fuselage is developed here for the following bodies used in wind tunnel experiments: the Large Rotor Test Apparatus (LRTA), the Rotor Test Apparatus (RTA), and the Higher Harmonic Control Aeroacoustic Rotor Test (HART).While the first two are used in the National Full-Scale Aerodynamics Complex (NFAC) at NASA Ames, California, the third one is used by DLR in the large low-speed facility of the German-Dutch wind tunnel in the Netherlands. The fuselage-induced velocity model is based on parameter identification of isolated fuselage-induced velocity data (computed by means of computational fluid dynamics, CFD) and is intended to be generic enough to be used for real helicopter fuselages as well. The accuracies obtained in reproducing the CFD data show a remaining average error of less or equal 5 of the peak-to-peak induced velocity range, which is considered sufficient for comprehensive code analysis.

HART↗

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.↗

NASA NTRS1994

Double vision: Remote sensing of a flux transfer event with ISEE 1 and 2

A flux transfer event recorded by the International Sun-Earth Explorers (ISEE) 1 and 2 spacecraft in the northern hemisphere near local noon is examined using analysis techniques developed recently for determination from single satellite magnetometer data of the orientation and cross-sectional shape of a two-dimensional disturbance moving along the magnetopause. The analysis is performed independently on the magnetic field data recorded by each satellite, enabling us to check the consistency of the results and thus to benchmark the method. The analysis is also extended to utilize the dual magnetometer measurements for determination of the event speed and size (which for a single spacecraft requires use of three-dimensional plasma velocity data to obtain a deHoffmann-Teller frame velocity) and for accommodating acceleration of the magnetopause normal to itself, which results in a curved spacecraft trajectory in the frame of reference moving with the disturbance. The analysis of the disturbance reveals that while its overall size is about 34,000 km in a direction parallel to the magnetopause but perpendicular to the event axis, the actual size of the bulge causing the field disturbance may have been as small as 9000 km with a dimension perpendicular to the magnetopause of the order of 1200 km. The bulge is found to be traveling at a speed of about 140 km/s toward the northern dawn quadrant of the dayside magnetopause. While plasma data from ISEE 2 provides evidence of plasma jetting, which suggests the event may be associated with reconnection, the orientation of the flux tube axis obtained from analysis is significantly different from the expected reconnection line direction. A discussion of possible interpretations of this bulge orientation and motion is provided.

Walthour, D. W.↗

NASA NTRS1989

Opposed jet diffusion flames of nitrogen-diluted hydrogen vs air - Axial LDA and CARS surveys; fuel/air rates at extinction

An experimental study of H-air counterflow diffusion flames (CFDFs) is reported. Coaxial tubular opposed jet burners were used to form dish-shaped CFDFs centered by opposing laminar jets of H2/N2 and air in an argon bath at 1 atm. Jet velocities for extinction and flame restoration limits are shown versus input H2 concentration. LDA velocity data and CARS temperature and absolute N2, O2 density data give detailed flame structure on the air side of the stagnation point. The results show that air jet velocity is a more fundamental and appropriate measure of H2-air CFDF extinction than input H2 mass flux or fuel jet velocity. It is proposed that the observed constancy of air jet velocity for fuel mixtures containing 80 to 100 percent H2 measure a maximum, kinetically controlled rate at which the CFDF can consume oxygen in air. Fuel velocity mainly measures the input jet momentum required to center an H2/N2 versus air CFDF.

Pellett, G. L.↗

NASA NTRS1993

LDV measurements in dynamically separated flows

Two component, phase averaged mean velocity data have been obtained with an Laser Doppler Velocimeter (LDV) system, on the upper surface, near the leading edge of an oscillating airfoil undergoing compressible dynamic stall. In particular, the effect of oscillation amplitude has been studied. The results show that at an oscillation amplitude of 10 degrees, a separation bubble forms, that eventually bursts on the upstroke, well beyond the static stall angle. At 2 degrees amplitude, the bubble forms on the upstroke, but dynamic stall occurs on the downstroke. The results reveal new flow physics and the data sets serve as valuable quantitative information for validation of unsteady flow codes at transitional Reynolds numbers. The maximum velocity seen in the flow is about 1.6 times the free stream value and it occurs slightly downstream of the suction peak location. Some of the measurement difficulties are also discussed.

Chandrasekhara, M. S.↗

NASA NTRS1993

Forcing function modeling for flow induced vibration

The fundamental forcing function unsteady aerodynamics for application to turbomachine blade row forced response are considered, accomplished through a series of experiments performed in a rotating annular cascade and a research axial flow turbine. In particular, the unsteady periodic flowfields downstream of rotating rows of perforated plates, airfoils and turbine blade rows are measured with a cross hot-wire and an unsteady total pressure probe. The unsteady velocity and static pressure fields were then analyzed harmonically and split into vortical and potential gusts, accomplished by developing a gust splitting analysis which includes both gust unsteady static pressure and velocity data. The perforated plate gusts closely were found to be linear theory vortical gusts, satisfying the vortical gust constraints. The airfoil and turbine blade row generated velocity perturbations did not satisfy the vortical gust constraints. However, the decomposition of the unsteady flow field separated the data into a propagating vortical component which satisfied these vortical gust constraints and a decaying potential component.

Fleeter, Sanford↗

NASA NTRS1982

Substructure within clusters of galaxies

Surface number density contour maps based on Dressler's (1976, 1980) studies of 65 rich clusters are presented to demonstrate the frequent occurrence of substructure in these dense systems. A prescription is given for examining the significance of such structure and it is shown that structure on scales equal to or larger than 0.24 Mpc (H0 = 100 km/s Mpc) is present in approximately 40% of the clusters in this sample. Many of the remaining clusters are elongated. The contour plots are useful for comparison with X-ray surface brightness maps. Together with available velocity data, they also serve warning that many rich clusters may not be simply characterized by a single core radius and velocity dispersion.

Geller, M. J.↗

NASA NTRS2009

GPS/MEMS IMU/Microprocessor Board for Navigation

A miniaturized instrumentation package comprising a (1) Global Positioning System (GPS) receiver, (2) an inertial measurement unit (IMU) consisting largely of surface-micromachined sensors of the microelectromechanical systems (MEMS) type, and (3) a microprocessor, all residing on a single circuit board, is part of the navigation system of a compact robotic spacecraft intended to be released from a larger spacecraft [e.g., the International Space Station (ISS)] for exterior visual inspection of the larger spacecraft. Variants of the package may also be useful in terrestrial collision-detection and -avoidance applications. The navigation solution obtained by integrating the IMU outputs is fed back to a correlator in the GPS receiver to aid in tracking GPS signals. The raw GPS and IMU data are blended in a Kalman filter to obtain an optimal navigation solution, which can be supplemented by range and velocity data obtained by use of (l) a stereoscopic pair of electronic cameras aboard the robotic spacecraft and/or (2) a laser dynamic range imager aboard the ISS. The novelty of the package lies mostly in those aspects of the design of the MEMS IMU that pertain to controlling mechanical resonances and stabilizing scale factors and biases.

Gender, Thomas K.↗

NASA NTRS2009

Alignment Jig for the Precise Measurement of THz Radiation

Javadi, Hamid H.↗

NASA NTRS1988

Measurement and prediction of propeller flow field on the PTA aircraft at speeds of up to Mach 0.85

High speed subsonic transports powered by advanced propellers provide significant fuel savings compared to turbofan powered transports. Unfortunately, however, propfans must operate in aircraft-induced nonuniform flow fields which can lead to high blade cyclic stresses, vibration and noise. To optimize the design and installation of these advanced propellers, therefore, detailed knowledge of the complex flow field is required. As part of the NASA Propfan Test Assessment (PTA) program, a 1/9 scale semispan model of the Gulfstream II propfan test-bed aircraft was tested in the NASA-Lewis 8 x 6 supersonic wind tunnel to obtain propeller flow field data. Detailed radial and azimuthal surveys were made to obtain the total pressure in the flow and the three components of velocity. Data was acquired for Mach numbers ranging from 0.6 to 0.85. Analytical predictions were also made using a subsonic panel method, QUADPAN. Comparison of wind-tunnel measurements and analytical predictions show good agreement throughout the Mach range.

Aljabri, Abdullah S.↗

NASA NTRS1983

Uppermantle anisotropy and the oceanic lithosphere

Published Rayleigh and Love wave phase and group velocity data have been inverted taking into account sphericity, anelastic dispersion, and transverse isotropy. For a PREM-type modular parameterization, the thickness of the high velocity mantle seismic lithosphere (LID) varies in thickness from about 30 km for young ocean to about 50 km for old ocean, much less than previous estimates based on isotropic inversion of similar data. This LID thickness is comparable to the elastic or flexural thickness found from studies of seamount loading and flexure at trenches, suggesting that the thickness of the lithosphere may be controlled by mineralogy, composition, or crystal orientation rather than by temperature alone.

Anderson, D. L.↗

NASA NTRS2005

MRI-Based Computational Fluid Dynamics in Experimental Vascular Models: Toward the Development of an Approach for Prediction of Cardiovascular Changes During Prolonged Space Missions

A priority of NASA is to identify and study possible risks to astronauts health during prolonged space missions [l]. The goal is to develop a procedure for a preflight evaluation of the cardiovascular system of an astronaut and to forecast how it will be affected during the mission. To predict these changes, a computational cardiovascular model must be constructed. Although physiology data can be used to make a general model, a more desirable subject-specific model requires anatomical, functional, and flow data from the specific astronaut. MRI has the unique advantage of providing images with all of the above information, including three-directional velocity data which can be used as boundary conditions in a computational fluid dynamics (CFD) program [2,3]. MRI-based CFD is very promising for reproduction of the flow patterns of a specific subject and prediction of changes in the absence of gravity. The aim of this study was to test the feasibility of this approach by reconstructing the geometry of MRI-scanned arterial models and reproducing the MRI-measured velocities using CFD simulations on these geometries.

Spirka, T. A.↗

NASA NTRS1972

Comparison of vertical profile turbulence structure with stellar observations.

Vertical profiles of microthermal turbulence structure have been obtained from balloon flights to altitudes near 25 km above mean sea level. Comparison of the observed turbulence structure with meteorological data and simultaneously acquired stellar scintillation data has been successful. For this comparison integrals over the observed turbulence structure were computed as required by theory. Turbulence and wind velocity data were also employed to successfully predict stellar irradiance spectra.

Bufton, J. L.↗

NASA NTRS1973

Comparison of vertical profile turbulence structure with stellar observations.

Bufton, J. L.↗

NASA NTRS1974

Evidence of a velocity gradient in the solar wind

Sector-boundary velocity data obtained by Mariner 5 near Venus and by Explorers 33, 34, and 35 near earth are analyzed to determine why higher velocities were measured at earth. Differences in the corresponding velocities are plotted as a function of the heliocentric latitude separation of Mariner and earth, and evidence of a significant latitude gradient in the solar wind is found. Several indirect arguments in support of a latitude gradient are presented, and it is concluded that if the solar wind velocity varies with latitude, latitudinal stresses may have a significant effect on the properties of the solar wind, such as the existence and character of the north-south component of the interplanetary magnetic field.

Smith, E. J.↗

NASA NTRS2000

Factors Controlling Upper-Troposphere Water Vapor

The seasonal changes of the upper-tropospheric humidity are studied with the water vapor data from the Microwave Limb Sounder on the National Aeronautics and Space Administration's Upper Atmosphere Research Satellite and the winds and vertical velocity data obtained from the European Centre for Medium-Range Weather Forecasts. Using the same algorithm for vertical transport as that used for horizontal transport (by Zhu and Newell), the authors find that the moisture in the tropical upper troposphere may be increased mainly by intensified local convection in a small portion, less than 10%, of the whole area between 40 degrees S and 40 degrees N. The contribution of large-scale background circulations and divergence of horizontal transport is relatively small in these regions. These dynamic processes cannot be revealed by the traditional analyses of moisture fluxes. The negative response suggested by Lindzen, with enhanced convection in the Tropics being accompanied by subsidence drying in the subtropics, also exists, but the latter does not apparently dominate in the moisture budget.

Zhu, Yong↗

NASA NTRS2002

Thermocouple Boundary Layer Rake

Apparatus and method for providing a velocity flow profile near a reference surface. A measuring device utilizes a plurality of thermojunction pairs to provide the velocity flow profile in accordance with behavior of a gas relative to a constant thickness strut which stands vertically from the reference surface such that the span is normal to the surface, and the chord is parallel to the surface along the initial flow direction. Each thermojunction is carried on either side of a heater formed on a measuring surface in a constant thickness portion of a strut. Additionally, each thermojunction of a given pair is located at a predetermined height from the reference surface. Gas velocity data obtained from temperature differentials from one side of the heater to the other at each successive height is utilized to generate the velocity and turbulence level profiles.

Danny P Hwang↗