Energetics of gas-surface interactions in transitional flows at entry velocities
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Wilmoth, R. G.↗
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Zonally-decoupled DSMC solutions of hypersonic blunt body wake flows
Direct simulation Monte Carlo (DSMC) solutions are presented for the hypersonic flow behind a blunt body in which the wake region is solved in a zonally-decoupled manner. The forebody flow is solved separately using either a DSMC or a Navier-Stokes method, and the forebody exit plane solution is specified as the inflow condition to the decoupled DSMC solution of the wake region. Results are presented for a 70-deg, blunted cone at flow conditions that can be accommodated in existing low-density wind tunnels with the Knudsen number based on base diameter ranging from 0.03 to 0.001. The zonally-decoupled solutions show good agreement with fully-coupled DSMC solutions of the wake flow densities and velocities. The wake closure predicted by the zonally-decoupled solutions is in better agreement with fully-coupled results than that predicted by a fully-coupled Navier-Stokes method indicating the need to account for rarefaction in the wake for the cases considered. The combined use of Navier-Stokes for the forebody with a decoupled DSMC solution for the wake provides an efficient method for solving transitional blunt-body flows where the forebody flow is continuum and the wake is rarefied.
Wilmoth, Richard G.↗
Hypersonic blunt body wake computations using DSMC and Navier-Stokes solvers
Numerical results obtained with direct simulation Monte Carlo (DSMC) and Navier-Stokes methods are presented for Mach 20 nitrogen flow about a 70-deg blunted cone. The flow conditions simulated are those that can be obtained in existing low-density hypersonic wind tunnels. Three sets of flow conditions are considered with freestream Knudsen numbers ranging from 0.03 to 0.001. The focus is on the wake structure: how does the wake structure change as a function of rarefaction, what are the afterbody levels of heating, and to what limits are continuum models realistic as rarefaction in the wake is progressively increased. Calculations are made with and without an afterbody sting. Results for the afterbody sting are emphasized in anticipation of an experimental study for the current flow conditions and model configuration. The Navier-Stokes calculations were made with and without slip boundary conditions. Comparisons of the results obtained with the two simulation methodologies are made for both flowfield structure and surface quantities.
Moss, James N.↗
Morphological, anatomical, and chemical characteristics of needle and branch samples of Siberian fir (Abies Siberica)
In August, 1991, needle and branch samples of Siberian fir were collected from undisturbed forest stands along an elevation gradient ranging from 2300 ft to 4450 ft. Four study sites were selected on west-facing slopes, and a standard set of measurements and collections was made. First-, second-, and third-year needles were collected for anatomical assessment. A visual assessment of the forest stand conditions at each site included an evaluation of canopy morphology needle, coloration, increment growth, and the state of health of a specific type of lichen. The heaviest damage to forest stands (extensive foliar loss, needle discoloration, dieback of terminal growth) occurs at an intermediate elevation site (3400 ft/1037 m). The least amount of damage was recorded at the lowest elevation site (2300 ft/701 m). Only slight damage occurs at the highest elevation site (4450 ft/1357 m). Some degree of flagging occurs at all sites. Several lines of evidence suggest that the damage occurring in this area is recent in origin (incipient).
Rock, B. N.↗
Advanced Solid Rocket Motor nozzle development status
This paper presents a status update of the design and development of an improved nozzle for the Advanced Solid Rocket Motor (ASRM). The ASRM nozzle incorporates advanced state-of-the-art design features and materials which contribute to enhanced safety, reliability, performance, and producibility for the space shuttle boosters. During 1992 the nozzle design progressed through a successful Preliminary Design Review (PDR). An improved ablative material development program also culminated in the selection of new standard and low density carbon cloth phenolic prepreg offering reduced variability and improved process attributes. A subscale motor test series to evaluate new materials and design features was also completed. An overview update of the matured design characteristics, supporting analysis, key development-program results and program status and plans is reported.
Kearney, W. J.↗
Red edge spectral measurements from sugar maple leaves
Many sugar maple stands in the northeastern United States experienced extensive insect damage during the 1988 growing season. Chlorophyll data and high spectral resolution spectrometer laboratory reflectance data were acquired for multiple collections of single detached sugar maple leaves variously affected by the insect over the 1988 growing season. Reflectance data indicated consistent and diagnostic differences in the red edge portion (680-750 nm) of the spectrum among the various samples and populations of leaves. These included differences in the red edge inflection point (REIP), a ratio of reflectance at 740-720 nm (RE3/RE2), and a ratio of first derivative values at 715-705 nm (D715/D705). All three red edge parameters were highly correlated with variation in total chlorophyll content. Other spectral measures, including the Normalized Difference Vegetation Index (NDVI) and the Simple Vegetation Index Ratio (VI), also varied among populations and over the growing season, but did not correlate well with total chlorophyll content. Leaf stacking studies on light and dark backgrounds indicated REIP, RE3/RE2 and D715/D705 to be much less influenced by differences in green leaf biomass and background condition than either NDVI or VI.
Vogelmann, J. E.↗
Wind-tunnel Investigation of the Stability and Control Characteristics of a Complete Model Equipped with a Vee Tail
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STABILIZERS↗
Three-dimensional hypersonic rarefied flow calculations using direct simulation Monte Carlo method
A summary of three-dimensional simulations on the hypersonic rarefied flows in an effort to understand the highly nonequilibrium flows about space vehicles entering the Earth's atmosphere for a realistic estimation of the aerothermal loads is presented. Calculations are performed using the direct simulation Monte Carlo method with a five-species reacting gas model, which accounts for rotational and vibrational internal energies. Results are obtained for the external flows about various bodies in the transitional flow regime. For the cases considered, convective heating, flowfield structure and overall aerodynamic coefficients are presented and comparisons are made with the available experimental data. The agreement between the calculated and measured results are very good.
Celenligil, M. Cevdet↗
The Los Alamos neutron spectrometer for the Lunar Scout-1 mission
We review the current status of the Los Alamos program to develop a neutron spectrometer for the Lunar Scout-1 mission, which is the first of two such missions to obtain global compositional, gravity, topography, and image maps of the lunar surface during nominal one-year missions. The neutron spectrometer will measure fast and slow (epithermal and thermal) neutrons in the ranges of 0.5 MeV to 25 MeV and 0.01 eV to more than 1 keV, respectively. The neutron spectrometer will consist of two independent instruments, a fast-neutron one, and a thermal and epithermal one. The measured neutron fluxes are very sensitive to hydrogen in the top meter of the lunar surface and provide additional information about lunar composition.
Auchampaugh, George↗
DSMC simulations of Mach 20 nitrogen flows about a 70 degree blunted cone and its wake
Numerical results obtained with the direct simulation Monte Carlo (DSMC) method are presented for Mach 20 nitrogen flow about a 70-deg blunted cone. The flow conditions simulated are those that can be obtained in existing low-density hypersonic wind tunnels. Three sets of flow conditions are simulated with freestream Knudsen numbers ranging from 0.03 to 0.001. The focus is to characterize the wake flow under rarefied conditions. This is accomplished by calculating the influence of rarefaction on wake structure along with the impact that an afterbody has on flow features. This data report presents extensive information concerning flowfield features and surface quantities.
Moss, James N.↗
Gamma ray spectrometer for Lunar Scout 2
We review the current status of the Los Alamos program to develop a high-resolution gamma-ray spectrometer for the Lunar Scout-II mission, which is the second of two Space Exploration Initiative robotic precursor missions to study the Moon. This instrument will measure gamma rays in the energy range of approximately 0.1 - 10 MeV to determine the composition of the lunar surface. The instrument is a high-purity germanium crystal surrounded by an CsI anticoincidence shield and cooled by a split Stirling cycle cryocooler. It will provide the abundance of many elements over the entire lunar surface.
Moss, C. E.↗
Development of a naming convention and data ma nagement system
This contract covered work in data management, acquisition, and analysis for the Earth Science and Applications Division (ESAD) of the Space Science Laboratory of MSFC. Under this contract, a naming convention and data management system were developed for ESAD data sets, data visualization, and standard data format issues were investigated, and specific data analysis and management needs were addressed for several ESAD projects and data sets. In the following sections, details of the research performed over the duration of this contract are summarized.
Mcnider, Richard T.↗
Using parallel banded linear system solvers in generalized eigenvalue problems
Subspace iteration is a reliable and cost effective method for solving positive definite banded symmetric generalized eigenproblems, especially in the case of large scale problems. This paper discusses an algorithm that makes use of two parallel banded solvers in subspace iteration. A shift is introduced to decompose the banded linear systems into relatively independent subsystems and to accelerate the iterations. With this shift, an eigenproblem is mapped efficiently into the memories of a multiprocessor and a high speed-up is obtained for parallel implementations. An optimal shift is a shift that balances total computation and communication costs. Under certain conditions, we show how to estimate an optimal shift analytically using the decay rate for the inverse of a banded matrix, and how to improve this estimate. Computational results on iPSC/2 and iPSC/860 multiprocessors are presented.
Zhang, Hong↗
Computation of flowfields for hypersonic flight at high altitudes
Recent direct simulation Monte Carlo methods are reviewed focusing on the nonequilibrium aspects of rarefied hypersonic flows typical of reentry conditions. The calculations identify the altitudes for which the onset of dissociation occurs, the magnitude of the surface temperature variations, the effect of the shock wave structure on the chemistry of a dissociating gas, and the radiation emisssion for reentry flowfields.
Moss, James N.↗
DSMC calculations for 70-deg blunted cone at 3.2 km/s in nitrogen
Numerical results obtained with the direct simulation Monte Carlo (DSMC) method are presented for Mach 15.6 nitrogen flow about a 70-deg spherically blunted cone at zero incidence. This flow condition is one of several generated in the Large Energy National Shock (LENS) tunnel during tests of a 15.24 cm diameter model with an afterbody sting. The freestream Knudsen number, based on model diameter, is 0.0023. The focus of the DSMC calculations is to characterize the near wake flow under conditions where rarefaction effects may influence afterbody aerothermal loads. This report provides information concerning computational details along with flowfield and surface quantities. Calculations show that the flow enveloping the test model is in thermal nonequilibrium and a sizable vortex develops in the near wake. Along the model baseplane the heating rates are about 0.6 percent of the forebody stagnation value while the maximum heating along the sting is about 4.2 percent of the forebody stagnation value. Comparison of a Navier-Stokes solution with the present calculations show good agreement for surface heating, pressure, and skin friction results.
Moss, J. N.↗
Direct simulation Monte Carlo and Navier-Stokes simulations of blunt body wake flows
Numerical results obtained with direct simulation Monte Carlo and Navier-Stokes methods are presented for a Mach-20 nitrogen flow about a 70-deg blunted cone. The flow conditions simulated are those that can be obtained in existing low-density hypersonic wind tunnels. Three sets of flow conditions are considered with freestream Knudsen numbers ranging from 0.03 to 0.001. The focus is on the wake structure: how the wake structure changes as a function of rare faction, what the afterbody levels of heating are, and to what limits the continuum models are realistic as rarefunction in the wake is progressively increased. Calculations are made with and without an afterbody sting. Results for the afterbody sting are emphasized in anticipation of an experimental study for the current flow conditions and model configuration. The Navier-Stokes calculations were made with and without slip boundary conditions. Comparisons of the results obtained with the two simulation methodologies are made for both flowfield structure and surface quantities.
WAKE STRUCTURE↗
Using parallel banded linear system solvers in generalized eigenvalue problems
Subspace iteration is a reliable and cost effective method for solving positive definite banded symmetric generalized eigenproblems, especially in the case of large scale problems. This paper discusses an algorithm that makes use of two parallel banded solvers in subspace iteration. A shift is introduced to decompose the banded linear systems into relatively independent subsystems and to accelerate the iterations. With this shift, an eigenproblem is mapped efficiently into the memories of a multiprocessor and a high speedup is obtained for parallel implementations. An optimal shift is a shift that balances total computation and communication costs. Under certain conditions, we show how to estimate an optimal shift analytically using the decay rate for the inverse of a banded matrix, and how to improve this estimate. Computational results on iPSC/2 and iPSC/860 multiprocessors are presented.
DISTRIBUTED MEMORY MULTIPROCES↗
Direct simulation Monte Carlo and Navier-Stokes simulations of blunt body wake flows
Numerical results obtained with direct simulation Monte Carlo and Navier-Stokes methods are presented for a Mach-20 nitrogen flow about a 70-deg blunted cone. The flow conditions simuulated are those that can be obtained in existing low-density hypersonic wind tunnels. Three sets of flow conditions are considered with freestream Knudsen numbers ranging from 0.03 to 0.001. The focus is on the wake structure: how the wake structure changes as a function of rarefaction, what the afterbody levels of heating are, and to what limits the continuum models are realistic as rarefaction in the wake is progressively increased. Calculations are made with and without an afterbody sting. Results for the after body sting are emphasizes in anticipation of an experimental study for the current flow conditions and model configuration. The Navier-Stokes calculations were made with and without slip boundary conditions. Comparisons of the results obtained with the two simulation methodologies are made for both flowfield structure and surface quantities.
Moss, James N.↗