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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

The aerodynamic characteristics of vortex ingestion for the F/A-18 inlet duct

A Reduced Navier-Stokes (RNS) solution technique was successfully combined with the concept of partitioned geometry and mesh generation to form a very efficient 3-D RNS code aimed at the analysis-design engineering environment. Partitioned geometry and mesh generation is a pre-processor to augment existing geometry and grid generation programs which allows the solver to (1) recluster an existing gridlife mesh lattice, and (2) perturb an existing gridfile definition to alter the cross-sectional shape and inlet duct centerline distribution without returning to the external geometry and grid generator. The present results provide a quantitative validation of the initial value space marching 3-D RNS procedure and demonstrates accurate predictions of the engine face flow field, with a separation present in the inlet duct as well as when vortex generators are installed to suppress flow separation. The present results also demonstrate the ability of the 3-D RNS procedure to analyze the flow physics associated with vortex ingestion in general geometry ducts such as the F/A-18 inlet. At the conditions investigated, these interactions are basically inviscid like, i.e., the dominant aerodynamic characteristics have their origin in inviscid flow theory.

Anderson, Bernhard H.↗
NASA NTRS1976

Closed cycle MHD power generation experiments using a helium-cesium working fluid in the NASA Lewis Facility

The MHD channel in the NASA Lewis Research Center was redesigned and used in closed cycle power generation experiments with a helium-cesium working fluid. The cross sectional dimensions of the channel were reduced to 5 by 16.5 cm to allow operation over a variety of conditions. Experiments have been run at temperatures of 1900-2100 K and Mach numbers from 0.3 to 0.55 in argon and 0.2 in helium. Improvements in Hall voltage isolation and seed vaporization techniques have resulted in significant improvements in performance. Typical values obtained with helium are Faraday open circuit voltage 141 V (92% of uBh) at a magnetic field strength of 1.7 T, power outputs of 2.2 kw for tests with 28 electrodes and 2.1 kw for tests with 17 electrodes. Power densities of 0.6 MW/cu m and Hall fields of about 1100 V/m were obtained in the tests with 17 electrodes, representing a factor of 18 improvement over previously reported results. The V-I curves and current distribution data indicate that while near ideal equilibrium performance is obtained under some conditions, no nonequilibrium power has been generated to date.

Sovie, R. J.↗
NASA NTRS2020

An Algorithm for Characterization of Fiber Aggregation in Composite Microstructures

Composite structures are susceptible to localized flaws, or variability, that drive global failure. To capture this variance, a multiscale model needs to be introduced that not only accurately represents the statistical nature of the composite microstructure but is also efficient. At the microscale, fiber aggregation creates local stress concentrations, where failure is likely to occur sooner than expected. A method of rapid microstructure generation, in conjunction with cluster characterization, is examined to develop accurate reproductions of 2D composite cross-sections. Parameterization of shape and size of fiber clusters is used to characterize representative volume elements. The discrete element method is used to generate pseudo-microstructures. The clustering parameters from the pseudo- and actual microstructure arrangements (obtained from micrographs) can be compared to determine the validity of the representative volume element generated with the discrete element method. Results show a promising approach to evaluating randomness of fiber distributions and how to accurately recreate microstructures for strength analysis.

Carbon fiber↗
NASA NTRS1979

Electron impact cross section measurements related to 'nuclear pumping'

In direct nuclear pumped lasers the high energy fission fragments generate a large number of secondary electrons and these electrons are mainly responsible for achieving the population inversion in the lasing media. Laboratory measurements concerned with these electron impact processes are summarized and new results are presented on rare gases, N2, CO, CF3I and UF6.

Trajmar, S.↗
NASA NTRS1983

Beam area determination for multiple-beam satellite communication applications

An exact analytical model and a simple numerical solution are presented for determining the surface area of the earth illuminated by a conical beam, with an elliptical cross section, emanating from a satellite. The model is used to generate sets of parametric curves for determination of the beam area as a function of the different satellite locations, beam locations, and beamwidths. Numerical results show that for a circular beam with a 0.25 deg beamwidth, the beam illuminating the northern Continental United States (CONUS) can cover an area about five times larger than the area covered by the same size beam illuminating the southern CONUS. Comparisons are also made with the available approximate methods.

Salmasi, A. B.↗
NASA NTRS1989

Hypersonic 3-D flow past winged bodies

The hypersonic flow past winged bodies is calculated using the 3D Navier-Stokes equations in both a space- and time-marching finite difference code. The bodies are a blunt ogive-cylinder with a delta wing planform and an elliptical body referred to as the allbody configuration. Laminar flow solutions for the ogive-cylinder-wing body and for the allbody configuration are presented. It is shown that the present technique has an excellent shock-capturing capability for all speed regimes. An axial zonal capability is incorporated to make the procedure more versatile. The grid system is created offline using an efficient hyperbolic grid generator which can handle the rapid variations in the body cross sections.

Chaussee, Denny S.↗
NASA NTRS1991

An examination of the damage tolerance enhancement of carbon/epoxy using an outer lamina of spectra (R)

Low velocity instrumented impact testing was utilized to examine the effects of an outer lamina of ultra-high molecular weight polyethylene (Spectra) on the damage tolerance of carbon epoxy composites. Four types of 16-ply quasi-isotropic panels (0, +45, 90, -45) were tested. Some panels contained no Spectra, while others had a lamina of Spectra bonded to the top (impacted side), bottom, or both sides of the composite plates. The specimens were impacted with energies up to 8.5 J. Force time plots and maximum force versus impact energy graphs were generated for comparison purposes. Specimens were also subjected to cross-sectional analysis and compression after impact tests. The results show that while the Spectra improved the maximum load that the panels could withstand before fiber breakage, the Spectra seemingly reduced the residual strength of the composites.

Lance, D. G.↗
NASA NTRS1992

Rate calculations for the simultaneous vibrational relaxation and dissociation of nitrogen

Experimental data on vibrational relaxation and dissociation rates in highly nonequilibrium gases are scarce. Recently there have been several attempts at generating these rates by direct calculation of inelastic collision cross-sections. Some issues that need to be considered if such calculations are to be used as a basis for analysis and design are examined. In particular, the following are examined: (1) collinear vs 3D scattering models, (2) accurate intermolecular potentials, (3) closed channels and acceleration schemes, (4) thermal averaging and thermal rates, and (5) code validation. It has been necessary to confront these issues during the course of N2-N2 and N2-N inelastic cross-section calculations.

Gonzales, David A.↗
NASA NTRS2011

Linearized T-Matrix and Mie Scattering Computations

We present a new linearization of T-Matrix and Mie computations for light scattering by non-spherical and spherical particles, respectively. In addition to the usual extinction and scattering cross-sections and the scattering matrix outputs, the linearized models will generate analytical derivatives of these optical properties with respect to the real and imaginary parts of the particle refractive index, and (for non-spherical scatterers) with respect to the ''shape'' parameter (the spheroid aspect ratio, cylinder diameter/height ratio, Chebyshev particle deformation factor). These derivatives are based on the essential linearity of Maxwell's theory. Analytical derivatives are also available for polydisperse particle size distribution parameters such as the mode radius. The T-matrix formulation is based on the NASA Goddard Institute for Space Studies FORTRAN 77 code developed in the 1990s. The linearized scattering codes presented here are in FORTRAN 90 and will be made publicly available.

Analytic linearization↗
NASA NTRS1986

External calibration of SIR-B Imagery with area-extended and point targets

Data collected by the Shuttle Imaging Radar-B (SIR-B) on two ascending orbits over a site in west-central Illinois were used to establish end-to-end transfer functions for conversion of the digital numbers on the eight-bit image to values of the radar backscattering coefficient, sigma(0). The transfer function for each data take was defined by the SIR response to an array of six calibrated point targets of known radar cross section and to a large number of area-extended targets, also with a known cross section, as measured by externally calibrated, truck-mounted scatterometers. In spite of variance in the SIR transmit power, end-to-end transfer functions generated from either point targets or area-extended targets were found to yield close agreement for a given pass, indicating that targets of known radar cross section can be used to provide transfer functions for orbital SAR. Although the use of area-extended targets yielded the most satisfactory results, the use of point targets is far simpler and may be the preferred alternative for many situations.

Dobson, M. C.↗
NASA NTRS1980

Determination of deep level capture cross sections in wide band-gap semiconductors by means of an electron beam

The paper presents a general theory for the determination of the short circuit current generated by a sinusoidally amplitude-modulated electron beam in the presence of recombination centers with an arbitrary number of charge states. It is shown that a measurement of the coherent phase shift with respect to the incident beam as a function of the modulation frequency of the beam ascertains the magnitudes of electron and hole capture cross sections. The surface exposed to the electron beam must have a negligible surface recombination velocity for the measurements to be unambiguous.

Von Roos, O.↗
NASA NTRS1984

Vortex generating flow passage design for increased film-cooling effectiveness and surface coverage

The fluid mechanics of the basic discrete hole film cooling process is described as an inclined jet in crossflow and a cusp shaped coolant flow channel contour that increases the efficiency of the film cooling process is hypothesized. The design concept requires the channel to generate a counter rotating vortex pair secondary flow within the jet stream by virture of flow passage geometry. The interaction of the vortex structures generated by both geometry and crossflow was examined in terms of film cooling effectiveness and surface coverage. Comparative data obtained with this vortex generating coolant passage showed up to factors of four increases in both effectiveness and surface coverage over that obtained with a standard round cross section flow passage. A streakline flow visualization technique was used to support the concept of the counter rotating vortex pair generating capability of the flow passage design.

Papell, S. S.↗
NASA NTRS1972

Photodetachment of an electron from selenide ion - The electron affinity and spin-orbit coupling constant for SeH.

The relative cross section for the gas phase photodetachment of an electron from SeH(-) was determined in the wavelength region 428 to 578 nm. An ion cyclotron resonance spectrometer was used to generate, trap, and detect the negative ions, and a 1000-W xenon arc lamp with a grating monochromator was employed as the light source. The cross section exhibited two sharp thresholds, whose positions remained unchanged for the photodetachment of SeD(-). As a result of these thresholds, the electron affinity and the spin-orbit coupling constant were evaluated.

Smyth, K. C.↗
NASA NTRS1996

Damage accumulation in closed cross-section, laminated, composite structures

The need for safe, lightweight, less expensive, and more reliable launch vehicle components is being driven by the competitiveness of the commercial launch market. The United States has lost 2/3 of the commercial lunch market to Europe. As low cost Russian and Chinese vehicles become available, the US market share could be reduced even further. This international climate is driving the Single Stage To Orbit (SSTO) program at NASA. The goal of the SSTO program is to radically reduce the cost of safe, routine transportation to and from space with a totally reusable launch vehicle designed for low-cost aircraft-like operations. Achieving this goal will require more efficient uses of materials. Composite materials can provide this program with the material and structural efficiencies needed to stay competitive in the international launch market place. In satellite systems the high specific properties, design flexibility, improved corrosion and wear resistance, increased fatigue life, and low coefficient of thermal expansion that are characteristic of composite materials can all be used to improve the overall satellite performance. Some of the satellites that may be able to take advantage of these performance characteristics are the Tethered Satellite Systems (TOSCIFER, AIRSEDS, TSS2, SEDS1, and SEDS2), AXAF, GRO, and the next generation Hubble Space Telescope. These materials can also be utilized in projects at the NASAIMSFC Space Optics Technology and System Center of Excellence. The successful implementation of composite materials requires accurate performance characterization. Materials characterization data for composite materials is typically generated using flat coupons of finite width. At the free edge of these coupons the stress state is exacerbated by the presence of stiffness and geometric discontinuities. The exacerbated stress state has been shown to dominate the damage accumulation in these materials and to have a profound affect on the material constants. Space structures typically have closed cross-sections, absent of free edges. As a result, composite material characterization data generated using finite width flat specimens does not accurately reflect the performance of the composite materials used in a closed cross-section structural configuration. Several investigators have recognized the need to develop characterization techniques for composite materials in closed cross-sectioned structures. In these investigations test methods were developed and cylindrical specimens were evaluated. The behavior of the cylindrical specimens were observed to depart from behavior typical of flat coupons. However, no attempts were made to identify and monitor the progression of damage in these cylindrical specimens during loading. The identification and monitoring of damage is fundamental to the characterization of composite materials in closed cross-section configurations. In the study reported here, a closed cross-sectioned test method was developed to monitor damage progression in 2 in. diameter cylindrical specimens and 1.5 in. finite width flat coupons subjected to quasi-static, tensile loading conditions. Damage in these specimen configurations was monitored using pulse echo ultrasonic, acoustic emission, and X-ray techniques.

Bucinell, Ronald B.↗
NASA NTRS1993

ERS-1 and Seasat scatterometer measurements of ocean winds: Model functions and the directional distribution of short waves

Calculation of accurate vector winds from scatterometers requires knowledge of the relationship between backscatter cross-section and the geophysical variable of interest. As the detailed dynamics of wind generation of centimetric waves and radar-sea surface scattering at moderate incidence angles are not well known, empirical scatterometer model functions relating backscatter to winds must be developed. Less well appreciated is the fact that, given an accurate model function and some knowledge of the dominant scattering mechanisms, significant information on the amplitudes and directional distributions of centimetric roughness elements on the sea surface can be inferred. accurate scatterometer model functions can thus be used to investigate wind generation of short waves under realistic conditions. The present investigation involves developing an empirical model function for the C-band (5.3 GHz) ERS-1 scatterometer and comparing Ku-band model functions with the C-band model to infer information on the two-dimensional spectrum of centimetric roughness elements in the ocean. The C-band model function development is based on collocations of global backscatter measurements with operational surface analyses produced by meteorological agencies. Strengths and limitations of the method are discussed, and the resulting model function is validated in part through comparison with the actual distributions of backscatter cross-section triplets. Details of the directional modulation as well as the wind speed sensitivity at C-band are investigated. Analysis of persistent outliers in the data is used to infer the magnitudes of non-wind effects (such as atmospheric stratification, swell, etc.). The ERS-1 C-band instrument and the Seasat Ku-band (14.6 GHz) scatterometer both imaged waves of approximately 3.4 cm wavelength assuming that Bragg scattering is the dominant mechanism. Comparisons of the C-band and Ku-band model functions are used both to test the validity of the postulated Bragg mechanism and to investigate the directional distribution of the imaged waves under a variety of conditions where Bragg scatter is dominant.

Freilich, Michael H.↗
NASA NTRS1976

Conceptual studies for new low-cost 64-m antennas

Recent software developments expedite design investigations of proposed new 64-m antenna structures. The software consists of programs to generate structure model data and a design program that chooses preferential cross sectional sizes of the structural members. Numerous new designs are summarized that can represent weight savings of from 25% to 50% with respect to the tipping weight of the existing Mars antenna. These designs provide a more favorable symmetrical support for the reflector backup and tend to provide superior surface accuracy for gravity, although not necessarily wind, loading on the antenna.

Levy, R.↗
NASA NTRS1988

Flow Analysis of Space Shuttle Feed Line 17-inch Disconnect Valve

A steady incompressible three-dimensional viscous flow analysis has been conducted for the Space Shuttle External Tank/Orbiter propellant feed line disconnect flapper valves with upstream elbows. The full Navier-Stokes code, INS3D, is modified to handle interior obstacles. Grids are generated by SVTGD3D code. Two dimensional initial grids in the flow cross section with and without the flappers are improved by elliptic smoothing to provide better orthogonality, clustering and smoothness to the three dimensional grid. The flow solver is tested for stability and convergence in the presence of interior flappers. An under-relaxation scheme has been incorporated to improve the solution stability. Important flow characteristics such as secondary flows, recirculation, vortex and wake regions, and separated flows are observed. Computed values for forces, moments, and pressure drop are in satisfactory agreement with water flow test data covering a maximum tube Reynolds number of 3.5 x 10(exp 6). The results will serve as a guide to improved design and enhanced testing of the disconnect.

Kandula, Max↗
NASA NTRS1992

Trajectory fitting in function space with application to analytic modeling of surfaces

A theory for representing a parameter-dependent function as a function trajectory is described. Additionally, a theory for determining a piecewise analytic fit to the trajectory is described. An example is given that illustrates the application of the theory to generating a smooth surface through a discrete set of input cross-section shapes. A simple procedure for smoothing in the parameter direction is discussed, and a computed example is given. Application of the theory to aerodynamic surface modeling is demonstrated by applying it to a blended wing-fuselage surface.

Barger, Raymond L.↗