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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Airborne Doppler lidar measurements

This paper describes recent measurements using coherent Doppler lidars operating at a wavelength of 10.6 microns aboard the NASA Ames Convair 990. The purpose of the measurements was to obtain data on the atmospheric wind fields and the distribution of the backscatter coefficient at 10.6 microns. A decription of the instruments is provided detailing the modifications incorporated following the 1981 test flights of the systems. The measurement program is outlined, and preliminary results are discussed.

Bilbro, James W.↗
NASA NTRS1987

Estimation of blade airloads from rotor blade bending moments

This paper presents a method for the estimation of blade airloads, based on the measurements of flap bending moments. In this procedure, the blade rotation in vacuum modes is calculated, and the airloads are expressed as an algebraic sum of the mode shapes, modal amplitudes, mass distribution, and frequency properties. The method was validated by comparing the calculated airload distribution with the original wind tunnel measurements which were made using ten modes and twenty measurement stations. Good agreement between the predicted and the measured airloads was found up to 0.90 R, but the agreement degraded towards the blade tip. The method is shown to be quite robust to the type of experimental problems that could be expected to occur in the testing of full-scale and model-scale rotors.

Bousman, William G.↗
NASA NTRS1990

Use of satellite data and modeling to assess the influence of stratospheric processes on the troposphere

Current research focused on the examination of the effects of ozone heating and Newtonian cooling on the linear stability of transient planetary waves. A finite difference numerical model was developed in which the basic state wind, temperature, and ozone distributions were constructed using ground-based and satellite data. Preliminary results indicate that ozone dynamics interaction may play a more important role in the stability and maintenance of planetary waves than previously thought, particularly in summer when the mean solar zenith angle is smallest and thus ozone heating largest. Examination of the finite amplitude interactions among radiation, ozone, and dynamics was carried out. Self-consistent, coupled equations governing the weakly nonlinear interactions are currently being analyzed to provide a better understanding of wave-mean flow interactions and ozone transport in a continuously stratified model of the troposphere-stratosphere coupled system.

Nathan, Terrence↗
NASA NTRS1992

Availability of hydrogen for lunar base activities

Hydrogen will be needed on a lunar base to make water for consumables, to provide fuel, and to serve as a reducing agent in the extraction of oxygen from lunar minerals. This study was undertaken in order to learn more about the abundance and distribution of solar-wind-implanted hydrogen. Hydrogen was found in all samples studied, with concentrations, varying widely depending on soil maturity, grain size, and mineral composition. Seven cores returned from the Moon were studied. Although hydrogen was implanted in the upper surface layer of the regolith, it was found throughout the cores due to micrometeorite reworking of the soil.

Bustin, Roberta↗
NASA NTRS1992

In-flight surface-flow measurements on a subsonic transport high-lift flap system

As part of a multiphased program for subsonic transport high-lift flight research, flight tests were conducted on the Transport Systems Research Vehicle (B737-100 aircraft) at the NASA Langley Research Center, to obtain detailed flow characteristics of the high-lift flap system for correlation with computational and wind-tunnel investigations. Pressure distributions, skin friction, and flow-visualization measurements were made on a triple-slotted flap system for a range of flap deflections, chord Reynolds numbers (10 to 21 million), and Mach numbers (0.16 to 0.36). Experimental test results are given for representative flap settings indicating flow separation on the fore-flap element for the largest flap deflection. Comparisons of the in-flight flow measurements were made with predictions from available viscous multielement computational methods modified with simple-sweep theory. Computational results overpredicted the experimentally measured pressures, particularly in the case involving separation of the fore lap, indicating the need for better modeling of confluent boundary layers and three-dimensional sweep effects.

Yip, Long P.↗
NASA NTRS1942

High-Speed Tests of Conventional Radial-Engine Cowlings

The drag characteristics of eight radial-engine cowlings have been determined over a wide speed range in the NACA 8-foot high-speed wind tunnel. The pressure distribution over all cowlings was measured, to and above the speed of the compressibility burble, as an aid in interpreting the force tests. One-fifth-scale models of radial-engine cowlings on a wing-nacelle combination were used in the tests.

Robinson, Russell G↗
NASA NTRS1946

Development of Wing Inlets

Lift, drag, internal flow, and pressure distribution measurements were made on a low-drag airfoil incorporating various air inlet designs. Two leading-edge air inlets are developed which feature higher lift coefficients and critical Mach than the basic airfoil. Higher lift coefficients and critical speeds are obtained for leading half of these inlet sections but because of high suction pressures near exist, slightly lower critical speeds are obtained for the entire inlet section than the basic airfoil.

AIRFOILS - DOUGLAS G-17 - CHAR , MOMENTS & ORDINAT↗
NASA NTRS1994

Particle acceleration by an interplanetary shock-pair seen at Ulysses at 3.15 AU

Observations from the HI-SCALE instrument on Ulysses of the ions and electrons associated with an interplanetary shock-pair at about 3.15 AU are presented. An empirical model is used to derive the evolution of the particle distribution in the solar wind frame. The forward shock is shown to be the primary source of ion acceleration, while the weaker and younger reverse shock is found to trap particles in its vicinity. There is also evidence of electron acceleration at the forward shock. We find evidence of multiple shock encounters for both ions and electrons.

Tappin, S. J.↗
NASA NTRS1997

Cooling Flow Spectra in Ginga Galaxy Clusters

The primary focus of this research project has been a joint analysis of Ginga LAC and Einstein SSS X-ray spectra of the hot gas in galaxy clusters with cooling flows is reported. We studied four clusters (A496, A1795, A2142 & A2199) and found their central temperatures to be cooler than in the exterior, which is expected from their having cooling flows. More interestingly, we found central metal abundance enhancements in two of the clusters, A496 and A2142. We have been assessing whether the abundance gradients (or lack thereof) in intracluster gas is correlated with galaxy morphological gradients in the host clusters. In rich, dense galaxy clusters, elliptical and SO galaxies are generally found in the cluster cores, while spiral galaxies are found in the outskirts. If the metals observed in clusters came from proto-ellipticals and proto-S0s blowing winds, then the metal distribution in intracluster gas may still reflect the distribution of their former host galaxies. In a research project which was inspired by the success of the Ginga LAC/Einstein SSS work, we analyzed X-ray spectra from the HEAO-A2 MED and the Einstein SSS to look for temperature gradients in cluster gas. The HEAO-A2 MED was also a non-imaging detector with a large field of view compared to the SSS, so we used the differing fields of view of the two instruments to extract spatial information. We found some evidence of cool gas in the outskirts of clusters, which may indicate that the nominally isothermal mass density distributions in these clusters are steepening in the outer parts of these clusters.

White, Raymond E., III↗
NASA NTRS2000

Numerical Model of the Plasma Sheath Generated by the Plasma Source Instrument Aboard the Polar Satellite

The plasma sheath generated by the operation of the Plasma Source Instrument (PSI) aboard the POLAR satellite is studied by using a 3-dimensional Particle-In-Cell (PIC) code. When the satellite passes through the region of low density plasma, the satellite charges to positive potentials as high as 4050Volts due to the photoelectrons emission. In such a case, ambient core ions cannot accurately be measured or detected. The goal of the onboard PSI is to reduce the floating potential of the satellite to a sufficiently low value so that the ions in the polar wind become detectable. When the PSI is operated, an ion-rich Xenon plasma is ejected from the satellite, such that the floating potential of the satellite is reduced and is maintained at about 2Volts. Accordingly, in our 3-dimensional PIC simulation, we considered that the potential of the satellite is 2Volts as a fixed bias. Considering the relatively high density of the Xenon plasma in the sheath (approx. 10 - 10(exp 3)/cc), the ambient plasma of low density (less than 1/cc) is neglected. In the simulations, the electric fields and plasma dynamics are calculated self-consistently. We found that an "Apple" shape positive potential sheath forms surrounding the satellite. In the region near the PSI emission, a high positive potential hill develops. Near the Thermal Ion Detection Experiment (TIDE) detector away from the PSI, the potentials are sufficiently low for the ambient polar wind ions to reach it. In the simulations, it takes about a hundred electron gyroperiods for the sheath to reach a quasi-steady state. This time is approximately the time taken by the heavy Xe(+) ions to expand up to about one average Larmor radius of electrons from the satellite surface. Using the steady state sheath, we performed trajectory calculations to characterize the detector response to a highly supersonic polar wind flow. The detected ions' velocity distribution shows significant deviations from a shifted Maxwellian in the ambient polar wind population. The deviations are caused by the effects of electric fields on the ions' motion as they traverse the sheath.

Leung, Wing C.↗
NASA NTRS2001

Numerical Model of the Plasma Sheath Generated by the Plasma Source Instrument Aboard the Polar Satellite

The plasma sheath generated by the operation of the Plasma Source Instrument (PSI) aboard the Polar satellite is studied by using a three-dimensional particle-in-cell (PIC) code. When the satellite passes through the region of low-density plasma, the satellite charges to positive potentials as high as 40-50 V, owing to the photoelectron emission. In such a case, ambient core ions cannot accurately be measured or detected. The goal of the onboard PSI is to reduce the floating potential of the satellite to a sufficiently low value so that the ions in the polar wind become detectable. When the PSI is operated, ion-rich xenon plasma is ejected from the satellite, such that the floating potential of the satellite is reduced and is maintained at approximately 2 V. Accordingly, in our three-dimensional PIC simulation we considered that the potential of the satellite is 2 V as a fixed bias. Considering the relatively high density of the xenon plasma in the sheath (10-10(exp 3)/cc), the ambient plasma of low density (<1/cc) is neglected. In the simulations the electric fields and plasma dynamics are calculated self-consistently. We found that an 'apple'-shape positive potential sheath forms surrounding the satellite. In the region near the PSI emission a high positive potential hill develops. Near the Thermal Ion Dynamics Experiment detector away from the PSI, the potentials are sufficiently low for the ambient polar wind ions to reach it. In the simulations it takes only about a couple of tens of electron gyroperiods for the sheath to reach a quasi steady state. This time is approximately the time taken by the heavy Xe(+) ions to expand up to about one average Larmor radius of electrons from the satellite surface. After this time the expansion of the sheath in directions transverse to the ambient magnetic field slows down because the electrons are magnetized. Using the quasi steady sheath, we performed trajectory calculations to characterize the detector response to a highly supersonic polar wind flow. The detected ions' velocity distribution shows significant deviations from a shifted Maxwellian in the ambient polar wind population. The deviations are caused by the effects of electric fields on the ions' motion as they traverse the sheath.

Singh, N.↗
NASA NTRS2003

Computations of Internal and External Axisymmetric Nozzle Aerodynamics at Transonic Speeds

Computational Fluid Dynamics (CFD) analyses of axisymmetric circular-arc boattail nozzles have been completed in support of NASA's Next Generation Launch Technology Program to investigate the effects of high-speed nozzle geometries on the nozzle internal flow and the surrounding boattail regions. These computations span the very difficult transonic flight regime, with shock-induced separations and strong adverse pressure gradients. External afterbody and internal nozzle pressure distributions computed with the Wind code are compared with experimental data. A range of turbulence models were examined in Wind, including an Explicit Algebraic Stress model (EASM). Computations on two nozzle geometries have been completed at freestream Mach numbers ranging from 0.6 to 0.9, driven by nozzle pressure ratios (NPR) ranging from 2.9 to 5. Results obtained on converging-only geometry indicate reasonable agreement to experimental data, with the EASM and Shear Stress Transport (SST) turbulence models providing the best agreement. Calculations completed on a converging-diverging geometry involving large-scale internal flow separation did not converge to a true steady-state solution when run with variable timestepping (steady-state). Calculations obtained using constant timestepping (time-accurate) indicate less variations in flow properties compared with steady-state solutions. This failure to converge to a steady-state solution was found to be the result of difficulties in using variable time-stepping with large-scale separations present in the flow. Nevertheless, time-averaged boattail surface pressure coefficient and internal nozzle pressures show fairly good agreement with experimental data. The SST turbulence model demonstrates the best over-all agreement with experimental data.

Dalbello, Teryn↗
NASA NTRS2003

Computational Study of Axisymmetric Off-Design Nozzle Flows

Computational Fluid Dynamics (CFD) analyses of axisymmetric circular-arc boattail nozzles operating off-design at transonic Mach numbers have been completed. These computations span the very difficult transonic flight regime with shock-induced separations and strong adverse pressure gradients. External afterbody and internal nozzle pressure distributions computed with the Wind code are compared with experimental data. A range of turbulence models were examined, including the Explicit Algebraic Stress model. Computations have been completed at freestream Mach numbers of 0.9 and 1.2, and nozzle pressure ratios (NPR) of 4 and 6. Calculations completed with variable time-stepping (steady-state) did not converge to a true steady-state solution. Calculations obtained using constant timestepping (timeaccurate) indicate less variations in flow properties compared with steady-state solutions. This failure to converge to a steady-state solution was the result of using variable time-stepping with large-scale separations present in the flow. Nevertheless, time-averaged boattail surface pressure coefficient and internal nozzle pressures show reasonable agreement with experimental data. The SST turbulence model demonstrates the best overall agreement with experimental data.

DalBello, Teryn↗
NASA NTRS2005

Lunar and Planetary Science XXXVI, Part 1

Contents include the following: Observations with Near Infrared Spectrometer for Hayabusa Mission in the Cruising Phase. First Results of Quadrantid Meteor Spectrum. Compositional Investigation of Binary Near-Earth Asteroid 66063 (1998 RO1): A Potentially Undifferentiated Assemblage. Impact-induced Hydrothermal Activity on Early Mars. HRTEM and EFTEM Studies of Phyllosilicate-Organic Matter Associations in Matrix and Dark Inclusions in the EET92042 CR2 Carbonaceous Chondrite. Volumetric Analysis of Martian Rampart Craters. High Pressure Melting of H-Chondrite: A Match for the Martian Basalt Source Mantle. MERView: A New Computer Program for Easy Display of MER-acquired M ssbauer Data. Distribution, Exchange, and Topographic Control of Subsurface Ice on Mars. Shock-induced Damage Beneath Normal and Oblique Impact Craters. Amphitrites Patera Studied from the Mars Express HRSC Data. Oxygen Isotope Microanalysis of Enveloping Compound Chondrules in CV3 and LL3 Chondrites. Gamma-Ray Irradiation in the Early Solar System and the Conundrum of the Lu-176 Decay Constant. Magnesium Isotope Mapping of Silica-rich Grains Having. Extreme Oxygen Isotope Anomalies Extreme Oxygen Isotopic Anomalies from Irradiation in the Early Solar System, Re-Examining the Role of Chondrules in Producing the Elemental Fractionations in Chondrites. Meteorite Data on the Solar Modulation of Galactic Cosmic Rays and an Inference on the Solar Activity Influence on Climate of the Earth. Volatiles Enrichments and Composition of Jupiter. Thinking Like a Wildcatter Prospecting for Methane in Arabia Terra, Mars. Size Distribution of Genesis Solar Wind Array Collector Fragments. Initial Subdivision of Genesis Early Science Polished Aluminum Collector. Presolar Graphite and Its Noble Gases. Young Pb-Isotopic Ages of Chondrules in CB Carbonaceous Chondrites. Fe Isotopic Composition of Martian Meteorites. Petrology and Geochemistry of Nakhlite MIL 03346: A New Martian Meteorite from Antarctica.

Source record↗
NASA NTRS2005

Line asymmetry in the Seyfert Galaxy NGC 3783

We have reanalyzed the 900 ks Chandra X-ray spectrum of NGC 3783, finding evidence on the asymmetry of the spectral absorption lines. The lines are fitted with a parametric expression that results from an analytical treatment of radiatively driven winds. The line asymmetry distribution derived from the spectrum is consistent with a non-spherical outflow with a finite optical depth. Within this scenario, our model explains the observed correlations between the line velocity shifts and the ionization parameter and between the line velocity shift and the line asymmetry. The present results may provide a framework for detailed testing of models for the dynamic and physical properties of warm absorber in Seyfert galaxies.

Ramirez, J. M.↗
NASA NTRS2005

Synergy Between probes and Orbiter

There are many ways in which the science return from a planetary mission is considerably enhanced by interactions between entry probes and a mission orbiter. Mission configuration aspects that are desirable include delivery of entry probes by the orbiter, and communication between probe and orbiter. Both of these mission aspects could greatly enhance access to key scientific sites that might not otherwise be accessible using delivery from say, a flyby, or employing direct communication from probes to Earth. Examples for Venus and Jupiter will be discussed. A second class of orbiter-probe interaction could better be termed direct probe-orbiter science collaboration. That would include, determining the global context of the entry probe sites from the orbiter, obtaining ground truth from the probe for remote sensing observations from the orbiter, observing the global and vertical distribution of key atmospheric trace species, and measuring the global and vertical distribution of clouds and winds. The importance of each of these items will be illustrated by particular examples.

Young, Richard E.↗