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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 505 records · Page 28
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NASA NTRS1988

IUE program SUGSD: Varability time scale of H Ly-alpha from Uranus

The scientific motivation for this program was to determine the time scale for the variability of the H Lyman-alpha emission from Uranus. The purpose of this series of observation is to determine its variability on shorter time scales. A series of observations was carried out in coordination with ESA to cover as completely as possible one 24 hour period of the Uranian H Lyman-alpha emission. The observations were obtained on April 23 and 24. Two additional ovservations on April 25 and 26 were obtained to search for longer term trends. A small modulation in the brightness was observed and the results presented.

Durrance, Samuel T.↗
NASA NTRS1988

SSME single-crystal turbine blade dynamics

A study was performrd to determine the dynamic characteristics of the Space Shuttle Main Engine high pressure fuel turbopump (HPFTP) blades made of single crystal (SC) material. The first and second stage drive turbine blades of HPFTP were examined. The nonrotating natural frequencies were determined experimentally and analytically. The experimental results of the SC second stage blade were used to verify the analytical procedures. The study examined the SC first stage blade natural frequencies with respect to crystal orientation at typical operating conditions. The SC blade dynamic response was predicted to be less than the directionally solidified base. Crystal axis orientation optimization indicated that the third mode interference will exist in any SC orientation.

Moss, Larry A.↗
NASA NTRS1986

Narrow band imagery in the 8-14 micron spectral region

The problem of deconvolution of the point source response function (PSF) for two-dimensional imaging infrared arrays is addressed. A variety of phenomena can lead to PSF degradation, ranging from atmospheric turbulence to the array itself. The maximum entropy algorithm is used to demonstrate that substantial image quality improvements are possible in the case of a PSF which is degraded by electronic rather than optical smearing. This result implies that IR arrays need not have perfect or even very good pixel-pixel crosstalk rejection ratios for use in astronomy.

Goebel, J. H.↗
NASA NTRS1986

Direct simulation of hypersonic transitional flow

A review of recent calculations obtained with Bird's direct simulation Monte Carlo (DSMC) method are presented for the transitional flowfield encountered at reentry conditions. Consequently, the emphasis is to simulate the real-gas effects resulting from a highly energetic nonequilibrium flow. The DSMC calculations for both wide-angle and slender bodies are compared with experimental and continuum calculations. The wide angle body calculations simulate the widward nose of the Shuttle Orbiter and projected aeroassisted orbital transfer vehicles. For the slender, blunted configurations, both two-dimensional and axisymmetric results are presented. Comparisons between the DSMC and continuum calculations show the altitude range where differences in flowfield structure and surface quantities become significant.

Moss, J. N.↗
NASA NTRS1987

High-resolution synchrotron X-ray study of the structure of La(1.8)Ba(0.2)CuO(4-y)

X-ray diffraction of La(1.8)Ba(0.2)CuO(4-y) reveals two macroscopically segregated tetragonal (K2NiF4-type) phases of nearly identical lattice parameter. Many peaks show additional broadening upon cooling. This broadening is consistent with a spontaneous monoclinic distortion, with an onset temperature of about 150 K, and is possibly relevant to the superconducting properties. Small single crystals of about 70 micron diameter within the powder aggregate are also studied and show a similar two-phase constituency and a resolvable peak splitting at low temperature.

Moss, S. C.↗
NASA NTRS1988

Nonequilibrium thermal radiation for an aeroassist flight experiment vehicle

The direct-simulation Monte Carlo method incorporating a dissociating and ionizing gas model for air with thermal radiation is used to characterize the hypersonic flow about an axisymmetric representation of an aeroassist flight experiment (AFE) vehicle, whose freestream conditions correspond to selected points along the entry, aerobraking, and exit phases of the trajectory. Calculations for two trajectory conditions indicate that the radiative heating of the AFE forebody is lower than the convective heating, but becomes significant as the maximum convective heating rate condition is approached.

Moss, James N.↗
NASA NTRS1988

Direct simulation of three-dimensional hypersonic flow about intersecting blunt wedges

The general three-dimensional direct simulation Monte Carlo method is used to study the hypersonic flow around two blunt wedges that intersect at a 90 deg angle. Results are obtained for the transitional flow regimes found at 85 and 100 km altitude with a reentry velocity of 7.5 km/s. The disturbance field in front of the double-wedge body is found to be larger than that produced by a single wedge. Surface pressures and flow densities are higher near the wedge intersection, whereas surface heating and shear streses are greater at locations removed from the corner. Results also show that three-dimensional flow structure occurs only near the wedge corner, and that the flow monotonically approaches the limiting two-dimensional wedge flow case in the spanwise direction.

Celenligil, M. Cevdet↗
NASA NTRS1987

An inexpensive S-band angle pointing technique for steering a narrow beam Ku-band antenna

A recently tested antenna pointing control system for gimbaled antennas has been developed. A modified TDRSS user transponder produces pointing error signals from the S-band forward link which in turn drive the Steering Control Electronics (SCE) to precision steer a S-/Ku-band Data and S-band Tracking (KDST) planar array. A successful test of the pointing and data handling capabilities is described and plans for further tests, incorporating additional refinements, are presented.

Line, Larry↗
NASA NTRS1988

Characterization of direct readout Si:Sb and Si:Ga infrared detector arrays for space-based astronomy

Preliminary test results from the evaluation of Si:Sb and Si:Ga 58 x 62-element infrared detector arrays are presented. These devices are being characterized under background conditions and readout rates representative of operation in orbiting, crogenically-cooled infrared observatories. The arrays are hybridized to silicon direct-readout multiplexers which allow random-access and nondestructive readout. Array performance optimization is being conducted with a flexible microcomputer-based drive and readoaut electronics system. Preliminary Si:Sb measurements indicate a sense node capacitance of 0.06 pF, peak (28-micron) responsivity above 3 A/W at 2V bias, read noise of 130 rms e(-), dark current approximately 10 e(-)/s, and a well capacity greater than 10 to the 5th e(-). The limited test data available on the performance of the Si:Ga array are also discussed.

Mckelvey, Mark E.↗
NASA NTRS1988

Grid generation and adaptation for the Direct Simulation Monte Carlo Method

A grid generation and adaptation procedure based on the method of transfinite interpolation is incorporated into the Direct Simulation Monte Carlo Method of Bird. In addition, time is advanced based on a local criterion. The resulting procedure is used to calculate steady flows past wedges and cones. Five chemical species are considered. In general, the modifications result in a reduced computational effort. Moreover, preliminary results suggest that the simulation method is time step dependent if requirements on cell sizes are not met.

Olynick, David P.↗
NASA NTRS1988

Direct simulation of three-dimensional flow about the AFE vehicle at high altitudes

Three-dimensional hypersonic rarefied flow about the Aeroassist Flight Experiment (AFE) vehicle was studied using the direct simulation Monte Carlo (DSMC) technique. Results are presented for the transitional flow regime encountered between 120 and 200 km altitudes with a reentry velocity of 9.92 km/s. In the simulations, a five-species reacting real-gas model that accounts for internal energies (rotational and vibrational) is used. The results indicate that the transitional effects are significant even at an altitude of 200 km and influence the overall vehicle aerodynamics. For the cases considered, the aerodynamic coefficients, surface pressures, convective heating, and flow field structure variations with rarefaction effects are presented.

Celenligil, M. Cevdet↗
NASA NTRS1988

Rarefied flow past a flat plate at incidence

Results of a numerical study using the direct simulation Monte Carlo (DSMC) method are presented for the transitional flow about a flat plate at 40 deg incidence. The plate has zero thickness and a length of 1.0 m. The flow conditions simulated are those experienced by the Shuttle Orbiter during reentry at 7.5 km/s. The range of freestream conditions are such that the freestream Knudsen number values are between 0.02 and 8.4, i.e., conditions that encompass most of the transitional flow regime. The DSMC simulations show that transitional effects are evident when compared with free molecule results for all cases considered. The calculated results demonstrate clearly the necessity of having a means of identifying the effects of transitional flow when making aerodynamic flight measurements as are currently being made with the Space Shuttle Orbiter vehicles. Previous flight data analyses have relied exclusively on adjustments in the gas-surface interaction models without accounting for the transitional effect which can be comparable in magnitude. The present calculations show that the transitional effect at 175 km would increase the Space Shuttle Orbiter lift-drag ratio by 90 percent over the free molecule value.

Dogra, Virendra K.↗
NASA NTRS1988

Direct simulation of AFE forebody and wake flow with thermal radiation

Calculated results for the flowfield structure and surface quantities are presented for an axisymmetric representation of an aeroassist flight experiment vehicle. The direct simulation Monte Carlo (DSMC) method is used to perform the calculations, since the flow is highly nonequilibrium about the vehicle during both the compression and expansion phases. The body configuration is an elliptically blunt nose followed by a skirt with a circular radius and an afterbody. Freestream conditions correspond to a single point along the entry trajectory at an altitude of 90 km and a velocity of 9.9 km/s. The calculations account for nonequilibrium in the translational and internal modes, dissociation, ionization, and thermal radiation. The degree of dissociation is large, but the maximum ionization is only about 2 percent by mole fraction. The bluntforebody flow experiences a high degree of thermal nonequilibrium in which the translational temperature is generally greater than the internal temperature. However, as the flow expands about the aerobrake skirt and afterbody, the internal temperature is generally greater than the translational temperature.

Moss, James N.↗
NASA NTRS1989

Three-dimensional flow simulation about the AFE vehicle in the transitional regime

The direct-simulation Monte Carlo technique is used to analyze the hypersonic rarefied flow about the three-dimensional NASA Aeroassist Flight Experiment vehicle. Results are given for typical transitional flows encountered during the vehicle's atmospheric entry from altitudes of 200-100 km with an entry velocity of 9.9 km/s. It is found that dissociation is important at altitudes of 110 km and below, and that transitional effects are significant even at an altitude of 200 km.

Celenligil, M. Cevdet↗
NASA NTRS1989

Influence of afterbodies on AOTV flows

The role of vibration-dissociation coupling in flows representative of AOTV's with afterbodies is discussed. A physical model designed to reflect the behavior of anharmonic diatomic molecules at high temperatures was developed and incorporated into the direct simulation Monte Carlo method of Bird (1976). The model leads to reduced dissociation and increased convective heating for flows with finite catalytic surfaces.

Olynick, David P.↗
NASA NTRS1989

Monte Carlo simulation of reentry plasmas

Attention is given to the treatment of ionization and plasma effects in the direct simulation Monte Carlo method. The requirements for accurate modeling of reentry plasmas are discussed along with the difficulties these requirements present. The current method for modeling such plasmas is reviewed and an alternative method is presented. Both methods are applied to the flow of a 10 km/s shock wave in air at 0.1 torr; a flowfield directly relevant to the projected aeroassisted orbital transfer vehicle. The results are compared and the differences between the methods are discussed.

Carlson, Ann B.↗