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At least 505 records · Page 28
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NASA NTRS2001

A Study of Heavy Precipitation Events in Taiwan During 10-13 August, 1994: Mesoscale Model Simulations - Part 2

Several heavy precipitation episodes occurred over Taiwan from August 10 to 13, 1994. Precipitation patterns and characteristics are quite different between the precipitation events that occurred from August 10 and I I and from August 12 and 13. In Part I (Chen et al. 2001), the environmental situation and precipitation characteristics are analyzed using the EC/TOGA data, ground-based radar data, surface rainfall patterns, surface wind data, and upper air soundings. In this study (Part II), the Penn State/NCAR Mesoscale Model (MM5) is used to study the precipitation characteristics of these heavy precipitation events. Various physical processes (schemes) developed at NASA Goddard Space Flight Center (i.e., cloud microphysics scheme, radiative transfer model, and land-soil-vegetation surface model) have recently implemented into the MM5. These physical packages are described in the paper, Two way interactive nested grids are used with horizontal resolutions of 45, 15 and 5 km. The model results indicated that Cloud physics, land surface and radiation processes generally do not change the location (horizontal distribution) of heavy precipitation. The Goddard 3-class ice scheme produced more rainfall than the 2-class scheme. The Goddard multi-broad-band radiative transfer model reduced precipitation compared to a one-broad band (emissivity) radiation model. The Goddard land-soil-vegetation surface model also reduce the rainfall compared to a simple surface model in which the surface temperature is computed from a Surface energy budget following the "force-re store" method. However, model runs including all Goddard physical processes enhanced precipitation significantly for both cases. The results from these runs are in better agreement with observations. Despite improved simulations using different physical schemes, there are still some deficiencies in the model simulations. Some potential problems are discussed. Sensitivity tests (removing either terrain or radiative processes) are performed to identify the physical processes that determine the precipitation patterns and characteristics for heavy rainfall events. These sensitivity tests indicated that terrain can play a major role in determining the exact location for both precipitation events. The terrain can also play a major role in determining the intensity of precipitation for both events. However, it has a large impact on one event but a smaller one on the other. The radiative processes are also important for determining, the precipitation patterns for one case but. not the other. The radiative processes can also effect the total rainfall for both cases to different extents.

Tao, Wei Kuo↗
NASA NTRS2001

An Experimental Study of the Ground Transportation System (GTS) Model in the NASA Ames 7- by 10-Ft Wind Tunnel

The 1/8-scale Ground Transportation System (GTS) model was studied experimentally in the NASA Ames 7- by 10-Ft Wind Tunnel. Designed for validation of computational fluid dynamics (CFD), the GTS model has a simplified geometry with a cab-over-engine design and no tractor-trailer gap. As a further simplification, all measurements of the GTS model were made without wheels. Aerodynamic boattail plates were also tested on the rear of the trailer to provide a simple geometry modification for computation. The experimental measurements include body-axis drag, surface pressures, surface hot-film anemometry, oil-film interferometry, and 3-D particle image velocimetry (PIV). The wind-averaged drag coefficient with and without boattail plates was 0.225 and 0.277, respectively. PIV measurements behind the model reveal a significant reduction in the wake size due to the flow turning provided by the boattail plates. Hot-film measurements on the side of the cab indicate laminar separation with turbulent reattachment within 0.08 trailer width for zero and +/- 10 degrees yaw. Oil film interferometry provided quantitative measurements of skin friction and qualitative oil flow images. A complete set of the experimental data and the surface definition of the model are included on a CD-ROM for further analysis and comparison.

Storms, Bruce L.↗
NASA NTRS2001

Apollo 10 - 11

This video gives overviews of the Apollo 10 and Apollo 11 missions to the moon, including footage from the launches and landings of the Command Module Columbia, which is used for both flights. The Apollo 10 crewmembers, Commander Thomas Stafford, Command Module Pilot John Young, and Lunar Module Pilot Eugene Cernan, are seen as they suit-up in preparation for launch and then as they experiment with the microgravity environment on their way to the moon. The moon's surface is seen in detail as the Command Module orbits at an altitude of 69 miles. The Apollo 11 crewmembers, Commander Neil Armstrong, Command Module Pilot Michael Collins, and Lunar Module Pilot Buzz Aldrin, are seen during various training activities, including simulated lunar gravity training, practicing collecting lunar material, and using the moonquake detector. Footage shows the approach and landing of the Lunar Module Eagle on the moon. Armstrong and Aldrin descend to the moon's surface, collect a sample of lunar dust, and erect the American flag. Eagle's liftoff from the moon is seen.

Source record↗
NASA NTRS2001

Scramjet Tests in a Shock Tunnel at Flight Mach 7, 10, and 15 Conditions

Tests of the Hyper-X scramjet engine flowpath have been conducted in the HYPULSE shock tunnel at conditions duplicating the stagnation enthalpy at flight Mach 7, 10, and 15. For the tests at Mach 7 and 10 HYPULSE was operated as a reflected-shock tunnel; at the Mach 15 condition, HYPULSE was operated as a shock-expansion tunnel. The test conditions matched the stagnation enthalpy of a scramjet engine on an aerospace vehicle accelerating through the atmosphere along a 1000 psf dynamic pressure trajectory. Test parameter variation included fuel equivalence ratios from lean (0.8) to rich (1.5+); fuel composition from pure hydrogen to mixtures of 2% and 5% silane in hydrogen by volume; and inflow pressure and Mach number made by changing the scramjet model mounting angle in the HYPULSE test chamber. Data sources were wall pressures and heat flux distributions and schlieren and fuel plume imaging in the combustor/nozzle sections. Data are presented for calibration of the facility nozzles and the scramjet engine model. Comparisons of pressure distributions and flowpath streamtube performance estimates are made for the three Mach numbers tested.

Rogers, R. C.↗
NASA NTRS2001

High Coverages of Hydrogen on a (10,0) Carbon Nanotube

The binding energy of H to a (10,0) carbon nanotube is calculated at 24, 50, and 100% coverage. Several different bonding configurations are considered for the 50% coverage case. Using the ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) approach, the average C-H bond energy for the most stable 50% coverage and for the 100% coverage are 57.3 and 38.6 kcal/mol, respectively. Considering the size of the bond energy of H2, these values suggest that it will be difficult to achieve 100% atomic H coverage on a (10,0) nanotube.

Bauschlicher, Charles W., Jr.↗
NASA NTRS2002

Vertical Mass, Momentum, Moisture, and Heat Fluxes in Hurricanes above 10 km during CAMEX-3 and CAMEX-4

The third and fourth NASA Convection and Moisture Experiments (CAMEX-3 and CAMEX-4) during the Atlantic hurricane seasons of 1998 and 2001, respectively, have yielded comprehensive multi-aircraft datasets using, both remote and in-situ instrumentation. Among these are high-frequency in-situ measurements of vertical wind, horizontal wind, temperature, and water vapor, made from NASA's DC-8 aircraft in the upper portions of the hurricane (typically above 10 km). Wind and temperature measurements were made at 20 hz by the NASA/Ames Meteorological Measurement System, while water vapor was measured at 1 hz by the NASA/JPL Laser Hygrometer. Fluxes of heat, momentum, and moisture at these levels are important, since modeling studies have shown that ice processes, which are dominant at temperatures below -40C (where the DC-8 flies) are important for hurricane intensification. Also, there are indications from satellite studies that latent heat release at DC-8 levels is significant, perhaps a third of those in the mid-troposphere. Preliminary results show that typical updrafts in the eyewall region are comparable to or higher than previous observations of tropical convection, with several instances of updraft magnitudes of 15 meters per second (the maximum observed was 21 meters per second). They also show significant supersaturations (10-20% or more) in the updrafts, which would enhance the latent heat release at the upper levels of the hurricane. This paper will examine the magnitude and distribution of small and mesoscale vertical fluxes of mass, momentum, moisture, and heat. The goal is to examine the role of these fluxes in the overall budgets of the respective quantities in the upper portions of the hurricane.

Pfister, Leonhard↗
NASA NTRS2003

STS-107 Flight Day 10 Highlights

This video shows the activities of the STS-107 crew (Rick Husband, Commander; William McCool, Pilot; Kalpana Chawla, David Brown, Michael Anderson, Laurel Clark, Mission Specialists; Ilan Ramon, Payload Specialist) during flight day 10 of the Columbia orbiter's final mission. Flight day 10 includes an interview by Mission Control of astronauts Brown, McCool, and Anderson, who answer questions on the mission's spaceborne experiments, as well as biographical and other questions. Much of the video is shot and narrated by Payload Specialist Ramon, who shows the crew members at work on experiments in the SpaceHab RDM (Research Double Module), and performing other tasks. Experiments featured in the video include SOFBALL (Structure of Flame Balls at Low Lewis-Number), the STARS (Space Technology and Research Students) experiments, and experiments on cancer and osteoporosis. Crew activities shown include making a video of Earth, and preparing for sleep. Earth views shown in the video include the Gulf of Aden, Ghana, Lake Chad, and the coast of North Carolina.

Source record↗
NASA NTRS2003

Progress Toward a Compact 0.05 K Magnet Refrigerator Operating from 10 K

Much of the most interesting information regarding our universe is hidden in the sub-millimeter, infrared, and x-rays bands of the spectrum, to which our atmosphere is largely opaque. Thus, missions exploring these bands are a very important part of NASA s Space Science program. Coincidentally, the most sensitive detectors in these spectral regions operate at extremely low temperatures, typically 0.05 - 0.10 K. Generally these temperatures will be achieved using magnetic refrigerators, also know as Adiabatic Demagnetization Refrigerators, or ADRs. Current ADRs, such as the one used in the XRS-II instrument on the Astro-E2 satellite, use a single-stage to cool detectors from 1.3 K to 0.06 K. The ADR is designed so that it can absorb the heat on the detector stage for at least 24 hours before it must stop, warm up to the helium bath temperature (1.3 K), and dump the accumulated heat. Future detector arrays will be much larger and will have higher heat dissipation. Furthermore, future missions will use mechanical cryocoolers to provide upper stage cooling, but they can only reach 4 - 10 K. Trying to scale heavy (-15 kg) single stage ADRs up to the higher heat loads and higher heat rejection temperatures required leads to unacceptably large systems. The GSFC Cryogenics Branch has developed the Continuous ADR (CADR) to solve this problem. The CADR consists of a series of ADR stages that sequentially pass heat from the load up to the high temperature heat sink. The stage connected to the load remains at a constant temperature. The continuous stage effectively decouples detector operation from ADR operation, allowing the ADR stages to be cycled much more rapidly. Rapid cycling leads to higher cooling power density. The cascading, multistage arrangement allows the magnetic refrigerant of each stage to be optimized for its own temperature swing. In the past year, we have made good progress toward a 0.05 to 10K system. A four-stage system that operates from 4.2 K was demonstrated. Magnetic shielding was added to eliminate inter-stage coupling. Improvements were made to superconducting and passive gas-gap heat switches. A second type of passive gas gap switch, one meant for use at higher temperature, was demonstrated. The presentation will focus primarily on these recent design improvements, and on the challenges that remain on the progress toward a system that will operate from 10 K or higher.

Canavan, Edgar↗
NASA NTRS2003

Supersonic Test of the 10-Inch Bifurcated Two-Stage Supersonic Inlet (BTSSI)

Experimental results from testing of a novel supersonic inlet model in NASA Glenn Research Center's 10- by 10-foot supersonic wind tunnel are presented. The patented inlet concept, called Two-Stage Supersonic Inlet (TSSI), incorporates a large cavity, or throat slot, in the supersonic diffuser intended to enhance the stability of the normal shock. The present embodiment of the concept is a bifurcated twin-duct) design. During the course of testing an unusual 'semi-started' mode of operation was encountered. The inlet was able to spill up to 30 percent of the captured airstream without fully expelling the normal shock. In this mode, the total pressure recovery dropped approximately 6 percent without increasing steady-state distortion. Dynamic instrumentation at the cowl lip station indicates the semi-start mode may be a series of unstart/restart cycles with frequency ranging from 0.2 to 20 Hz. Engine face total pressure measurements indicate a modest impact due to this event. However, since the current test article does not have a representative subsonic diffuser (and is in fact separated), it is unclear how this mode of operation would effect an engine. Further investigation of this phenomenon is required before it is fully understood. Prior testing of the TSSI concept allowed extension of fully started inlet operation to regions of significantly reduced supply flow without reducing recovery. The test article was a smaller scale than the present test and was a single duct design. In the present test, the expanded range of stable operation with high recovery was not realized.

Carlin, C. M.↗
NASA NTRS2003

The Effect of Heat Treatment on the Fatigue Behavior of Alloy 10

The results of the fatigue evaluation on Alloy 10, run under NASA's Ultrasafe Project, are the subject of this report. Crack growth evaluation will be examined in a separate report. The eight heat treatments studied were designed to evaluate the effect of solution temperature, cooling rate, and stabilization on key mechanical properties of Alloy 10, including fatigue life. Two temperatures were studied, 750 and 1300 F, which represent projected application temperatures for the bore and rim locations in a disk. In addition to fatigue life, the cyclic stress-strain response and failure modes of the fatigue specimens are also reviewed in this report.

Gayda, John↗
NASA NTRS1961

Free-Flight Skin-Temperature and Surface-Pressure Measurements on a Highly Polished Nose Having a 100 deg Total-Angle Cone and a 10 deg Half-Angle Conical Flare Section up to a Mach Number of 4.08

The skin temperature and surface pressure were measured on a large-scale, highly polished nose having a relatively sharp-tipped 100 deg total-angle cone followed by a conical flare section of 10 deg half-angle. The measurements were obtained in flight from a rocket-propelled model up to a peak Mach number of 4.08 and a peak Reynolds number of 22 x 10(exp 6) per foot. Temperature distributions indicated that the heating on the forward 3.5 inches of the 100 deg cone was lower than the heating on the rearward portion. Likewise, measured temperatures on the flare portion of the test nose were generally lower than the temperatures on the 100 deg cone portion. The data indicated that the local Reynolds numbers of transition, based on calculated boundary-layer momentum thicknesses, ranged from 530 to 940 for a Mach number range from 2.72 to 3.75. Comparison of measured cone pressures with theory for a sharp cone showed that theory overestimates the cone pressures. Pressure measurements on the flare portion of the nose showed that in the lower speed range the flow expands below atmospheric pressure in going from the cone to the flare; however, as the speed increased, the expansion diminished and for speeds greater than a Mach number of approximately 3.0 the flare pressure coefficients were at or near a value of zero.

Rashis, Bernard↗
NASA NTRS2004

RXTE All-Sky Slew Survey. Catalog of X-Ray Sources at B Greater Than 10 deg

We report results of a serendipitous hard X-ray (3-20 keV), nearly all-sky (absolute value of b greater than l0 deg.) survey based on RXTE/PCA observations performed during satellite reorientations in 1996-2002. The survey is 80% (90%) complete to a 4(sigma) limiting flux of approx. = 1.8 (2.5) x 10(exp -l1) erg/s sq cm in the 3-20 keV band. The achieved sensitivity in the 3-8 keV and 8-20 keV subbands is similar to and an order of magnitude higher than that of the previously record HEAO-1 A1 and HEAO-1 A4 all-sky surveys, respectively. A combined 7 x 10(exp 3) sq. deg area of the sky is sampled to flux levels below l0(exp -11) erg/ s sq cm (3-20 keV). In total 294 sources are detected and localized to better than 1 deg. 236 (80%) of these can be confidently associated with a known astrophysical object; another 22 likely result from the superposition of 2 or 3 closely located known sources. 35 detected sources remain unidentified, although for 12 of these we report a likely soft X-ray counterpart from the ROSAT all-sky survey bright source catalog. Of the reliably identified sources, 63 have local origin (Milky Way, LMC or SMC), 64 are clusters of galaxies and 100 are active galactic nuclei (AGN). The fact that the unidentified X-ray sources have hard spectra suggests that the majority of them are AGN, including highly obscured ones (N(sub H) greater than l0(exp 23)/sq cm). For the first time we present a log N-log S diagram for extragalactic sources above 4 x l0(exp -12) erg/ s sq cm at 8-20 keV. Key words. cosmo1ogy:observations - diffuse radiation - X-rays general

Revnivtsev, M.↗
NASA NTRS1995

Exhaust Gas Modeling Effects on Hypersonic Powered Simulation at Mach 10

A numerical study was performed to investigate the accuracy and validity of cold-gas simulation of actual hot scramjet exhaust within a Mach 10 free stream over a representative single-stage-to-orbit airbreathing configuration. In particular, exhausts of various noncombusting chemistry models were studied to characterize their effects on the vehicle aftbody performance and the plume flow field definition. Two approximations of the hot scramjet combustion products were utilized to determine the requirement for expensive, multi-species numerical modeling, and to establish a baseline for the validation of cold-gas simulation. Cold-gas simulation at Mach 10 is shown to be a viable technique using an appropriate thermally perfect gas mixture for reproducing hot scramjet exhaust effects.

Tatum, Kenneth E.↗
NASA NTRS1992

Reynolds Number and Cowl Position Effects for a Generic Sidewall Compression Scramjet Inlet at Mach 10: A Computational and Experimental Investigation

Reynolds number and cowl position effects on the internal shock structure and the resulting performance of a generic three-dimensional sidewall compression scramjet inlet with a leading edge sweep of 45 degrees at Mach 10 have been examined both computationally and experimentally. Prior to the experiment, a three-dimensional Navier-Stokes code was adapted to perform preliminary parametric studies leading to the design of the present configuration. Following this design phase, the code was then utilized as an analysis tool to provide a better understanding of the flow field and the experimental static pressure data for the final experimental configuration. The wind tunnel model possessed 240 static pressure orifices distributed on the forebody plane, sidewalls, and cowl and was tested in the NASA Langley 31 Inch Mach 10 Tunnel.

Holland, Scott D.↗
NASA NTRS2004

Performance and Flowfield Measurements on a 10-inch Ducted Rotor VTOL UAV

A ducted fan VTOL UAV with a 10-inch diameter rotor was tested in the US Army 7-by 10-Foot Wind Tunnel. The test conditions covered a range of angle of attack from 0 to 110 degrees to the freestream. The tunnel velocity was varied from 0 (simulating a hover condition) to 128 ft/sec in propeller mode. A six-component internal balance measured the aerodynamic loads for a range of model configurations. including the isolated rotor, the isolated duct, and the full configuration of the duct and rotor. For some conditions, hotwire velocity surveys were conducted along the inner and outer surface of the duct and across the downstream wake. In addition, fluorescent oil flow visualization allowed the flow separation patterns inside and outside of the duct to be mapped for a few test conditions. Two different duct shapes were tested to determine the performance effects of leading edge radius. For each duct, a range of rotor tip gap from 1%R to 4.5%R was tested to determine the performance penalty in hover and axial flight. Measured results are presented in terms of hover performance, hover performance in a crosswind, and high angle of attack performance in propeller mode. In each case, the effects of both tip gap and duct leading edge radius are illustrated using measurements. Some of the hover performance issues were also studied using a simple analytical method, and the results agreed with the measurements.

Martin, Preston↗
NASA NTRS2005

Overview With Results and Lessons Learned of the X-43A Mach 10 Flight

This paper provides an overview of the final flight of the NASA X-43A project. The project consisted of three flights, two planned for Mach 7 and one for Mach 10. The third and final flight, November 16, 2004, was the first Mach 10 flight demonstration of an airframe-integrated, scramjet-powered, hypersonic vehicle. The goals and objectives for the project as well as those for the third flight are presented. The configuration of the Hyper-X stack including the X-43A, Hyper-X launch vehicle, and Hyper-X research vehicle adapter is discussed. The second flight of the X-43A was successfully conducted on March 27, 2004. Mission differences, vehicle modifications and lessons learned from the second flight as they applied to the third flight are also discussed. An overview of flight 3 results is presented.

Marshall, Laurie A.↗
NASA NTRS2005

Scramjet Development Tests Supporting the Mach 10 Flight of the X-43

The Hyper-X Project s successful third flight of the X-43 at near Mach 10 in 2004 proved the potential for airbreathing propulsion at hypersonic speeds. The engine flowpath used in the X-43 research vehicle was developed and evaluated in a systematic series of ground tests in the NASA HyPulse Shock Tunnel at conditions duplicating Mach 10 flight using a full scale height, partial width engine model of the flight engine. Tests were conducted over a range of equivalence ratios from 0.8 to 1.6 using hydrogen and a mixture of two-percent silane in hydrogen fuels. Silane gas was used as an ignition aid during the short duration of the pulse facility tests. Variation of the engine inflow conditions, pressure, temperature, and Mach number, were parametrically varied during the test entries to broaden the database over the expected uncertainty in the flight conditions. A review of the ground test technique and comparisons of the ground test pressures along with selected flight data are presented.

Rogers, R. C.↗
NASA NTRS2004

Synthesis, Characterization, and Optical Properties of a Cyano-Functionalized 4,5,9,10-tetraaryl-l,6-dioxapyrene

5,10-Di(4-cyanophenyl)-4,9-di(4-methylphenyl)-1,6-dioxapyrene ( CN-diox), a symmetrically substituted 4,5,9,10-tetraaryldioxapyrene, was synthesized in seven steps from 1,4-dihydroxynaphthalene. The synthetic methodology incorporated a base-catalyzed ring-closure process followed by dehydration to introduce the first tetraaryl- 1,6-dioxapyrene. Crystal structure and electrochemical analysis were performed to directly compare the properties of CN-diox to previously reported dioxapyrene derivatives, specifically 1,6-dioxapyrene (Diox) and 4,9-diethyl-2,7-dimethyl- 1,6-dioxapyrene (Alkyl-diox). Optical spectroscopy studies were performed to evaluate the potential of the 1,6-dioxapyrenes as fluorescent probes. CN-diox revealed a broad absorption centered near 450 nm (epsilon = 31,900/M/cm) in THF with a corresponding fluorescence at 619 nm (Phi(sub f) = 0.011). This was in sharp contrast to both Diox and Alkyl-diox which displayed broad absorption bands near 400 nm (epsilon approx. 5,000-10,000/M/cm) in THF with corresponding fluorescence near 500 nm (Phi(sub f) = 0.059 and 0.082 for Diox and Alkyl-diox, respectively). The luminescence of CN-diox was found to be solvatochromic (lambda(sub max) = 619 nm-644 nm) with single exponential lifetimes of less than 1.3 ns. Neither Diox nor Alkyl-diox showed solvatochromic properties.

Tyson, Daniel S.↗