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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 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Evaluation of finite-element models and stress-intensity factors for surface cracks emanating from stress concentrations

A re-evaluation of the 3-D finite-element models and methods used to analyze surface crack at stress concentrations is presented. Previous finite-element models used by Raju and Newman for surface and corner cracks at holes were shown to have ill-shaped elements at the intersection of the hole and crack boundaries. Improved models, without these ill-shaped elements, were developed for a surface crack at a circular hole and at a semi-circular edge notch. Stress-intensity factors were calculated by both the nodal-force and virtual-crack-closure methods. Comparisons made between the previously developed stress-intensity factor equations and the results from the improved models agreed well except for configurations with large notch-radii-to-plate-thickness ratios. Stress-intensity factors for a semi-elliptical surface crack located at the center of a semi-circular edge notch in a plate subjected to remote tensile loadings were calculated using the improved models.

Tan, P. W.↗
NASA NTRS1990

Numerical prediction of turbulent flow over airfoil sections with a new nonequilibrium turbulence model

A new nonequilibrium turbulence closure model has been developed for computing wall bounded two-dimensional turbulent flows. This two-layer eddy viscosity model was motivated by the success of the Johnson-King model in separated flow regions. The influence of history effects are described by an ordinary differential equation developed from the turbulent kinetic energy equation. The performance of the present model has been evaluated by solving the flow around three airfoils using the Reynolds time-averaged Navier-Stokes equations. Excellent results were obtained for both attached and separated turbulent flows about the NACA 0012 airfoil, the RAE 2822 airfoil, and the Integrated Technology A 153W airfoil. Based on the comparison of the numerical solutions with the available experimental data, it is concluded that the new nonequilibrium turbulence model accurately captures the history effects of convection and diffusion on turbulence.

Ahmed, S.↗
NASA NTRS1989

Intrinsic fatigue crack propagation in aluminum-lithium alloys - The effect of gaseous environments

Gaseous environmental effects on intrinsic fatigue crack growth are significant for the Al-Li-Cu alloy 2090, peak aged. For both moderate Delta K-low R and low Delta K-high R regimes, crack growth rates decrease according to the environment order: purified water vapor, moist air, helium and oxygen. Gaseous environmental effects are pronounced near threshold and are not closure dominated. Here, embrittlement by low levels of H2O (ppm) supports hydrogen embrittlement and suggests that molecular transport controlled cracking, established for high Delta K-low R, is modified near threshold. Localized crack tip reaction sites or high R crack opening shape may enable the strong, environmental effect at low levels of Delta K. Similar crack growth in He and O2 eliminates the contribution of surface films to fatigue damage in alloy 2090. While 2090 and 7075 exhibit similar environmental trends, the Al-Li-Cu alloy is more resistant to intrinsic corrosion fatigue crack growth.

Piascik, Robert S.↗
NASA NTRS1990

Infrared reflectance measurements of the insulator-metal transition in solid hydrogen

Reflectance measurements on solid hydrogen to 177 GPa (1.77 Mbar) have been performed from near-infrared to ultraviolet wavelengths (0.5 to 3 eV). Above 150 GPa characteristic free-electron behavior in the infrared region is observed to increase sharply with increasing pressure. Analysis of volume dependence of the plasma frequency obtained from Drude-model fits to the spectra indicates that the pressure of the insulator-metal transition is 149 (+ or - 10) GPa at 295 K. The measurements are consistent with metallization by closure of an indirect gap in the molecular solid.

Mao, H. K.↗
NASA NTRS1990

A numerical study of the effects of reverse sweep on a scramjet inlet performance

A comparative numerical study of performance parameters of a similar and an opposite sweep sidewall compression inlet is made. The focus of the study is the investigation of the impact of alternate backward-forward sweep on the compression sidewalls as opposed to back-ward sweep on all the sidewalls. Two equivalent scramjet inlet configurations are designed for this purpose. These inlets have the same wetted areas of compression and expansion and same height and width; but in one inlet all the compression surface are swept back (similar sweep inlet) whereas in the other inlet, alternate surfaces are swept backward and forward (opposite sweep inlet). The cowl closure in both cases begins at the start of the throat region. A three-dimensional Navier-Stokes code is used to calculate the flow through these inlets. Results of these calculations are used to compare the two designs for their performance and flow quality. Effects of boundary- layer ingestion on the performance and overall flow features are also investigated.

Kumar, Ajay↗
NASA NTRS1990

A test matrix sequencer for research test facility automation

The hardware and software configuration of a Test Matrix Sequencer, a general purpose test matrix profiler that was developed for research test facility automation at the NASA Lewis Research Center, is described. The system provides set points to controllers and contact closures to data systems during the course of a test. The Test Matrix Sequencer consists of a microprocessor controlled system which is operated from a personal computer. The software program, which is the main element of the overall system is interactive and menu driven with pop-up windows and help screens. Analog and digital input/output channels can be controlled from a personal computer using the software program. The Test Matrix Sequencer provides more efficient use of aeronautics test facilities by automating repetitive tasks that were once done manually.

Mccartney, Timothy P.↗
NASA NTRS1990

Critical behavior in the hydrogen insulator-metal transition

The vibrational Raman spectrum of solid hydrogen has been measured from 77 to 295 K in the vicinity of the recently observed insulator-metal transition and low-temperature phase transition at 150 gigapascals. The measurements provide evidence for a critical point in the pressure-temperature phase boundary of the low-temperature transition. The result suggests that below the critical temperature the insulator-metal transition changes from continuous to discontinuous, consistent with the general criteria originally proposed by Mott (1949) for metallization by band-gap closure. The effect of temperature on hydrogen metallization closely resembles that of the lower-pressure insulator-metal transitions in doped V2O3 alloys.

Hemley, R. J.↗
NASA NTRS1990

Evolution and interaction of two- and three-dimensional instability waves

The present work is concerned with the nonlinear interactions of high-amplitude two- and three-dimensional instability waves in jets. A jet is excited by multifrequency axisymmetric and helical modes. Formulations are presented here for the nonlinear development of both the amplitudes and phases of the instability waves. The development of these waves are also coupled with the development of the mean flow and the background turbulence. In formulating this model it is assumed that each flow component can be characterized by conservations equations supplemented by closure models.

Mankbadi, R. R.↗
NASA NTRS1990

Past and present environmental control and life support systems on manned spacecraft

The spacecraft environmental control and life support systems (ECLSS) for Mercury, Gemini, Apollo, Skylab, Spacelab, the Space Shuttle Orbiter, and Space Station Freedom are reviewed, in addition to the ECLSS on Soviet spacecraft Vostok, Voskhod, Soyuz, Salyut Space Stations, the Buran Space Shuttle, and the Mir Space Station. Focus is placed on atmosphere control and supply, atmosphere revitalization, potable and supply water systems, waste-management systems, temperature and humidity control, water recovery and management, and fire detection and suppression. It is noted that the ECLSS evolution will continue during the lifetime of Space Station Freedom, leading to further simplifications and closure of the system which will become a controlled ecological life support system (CELSS).

Diamant, Bryce L.↗
NASA NTRS1990

Numerical computation of viscous flow about unconventional airfoil shapes

A new two-dimensional computer code was developed to analyze the viscous flow around unconventional airfoils at various Mach numbers and angles of attack. The Navier-Stokes equations are solved using an implicit, upwind, finite-volume scheme. Both laminar and turbulent flows can be computed. A new nonequilibrium turbulence closure model was developed for computing turbulent flows. This two-layer eddy viscosity model was motivated by the success of the Johnson-King model in separated flow regions. The influence of history effects are described by an ordinary differential equation developed from the turbulent kinetic energy equation. The performance of the present code was evaluated by solving the flow around three airfoils using the Reynolds time-averaged Navier-Stokes equations. Excellent results were obtained for both attached and separated flows about the NACA 0012 airfoil, the RAE 2822 airfoil, and the Integrated Technology A 153W airfoil. Based on the comparison of the numerical solutions with the available experimental data, it is concluded that the present code in conjunction with the new nonequilibrium turbulence model gives excellent results.

Ahmed, S.↗
NASA NTRS1989

Numerical simulation of nonlinear development of instability waves

The nonlinear interactions of high amplitude instability waves in turbulent jets are described. In plane shear layers Riley and Metcalf (1980) and Monkewitz (1987) have shown that these interactions are dependent, among other parameters, on the phase-difference between the two instability waves. Therefore, here researchers consider the nonlinear development of both the amplitudes and the phase of the instability waves. The development of these waves are also coupled with the development of the mean flow and the background turbulence. In formulating this model it is assumed that each of the flow components can be characterized by conservation equations supplemented by closure models. Results for the interactions between the two instability waves under high-amplitude forcing at fundamental and subharmonic frequencies are presented here. Qualitative agreements are found between the present predictions and available experimental data.

Mankbadi, Reda R.↗
NASA NTRS1989

Three-Man Solid Electrolyte Carbon Dioxide Electrolysis Breadboard

The development of the Three-Man (2.2 lb CO2/man-day) Solid Electrolyte CO2 Electrolysis Breadboard consisted of a Phase 1 and 2 effort. The Phase 1 effort constituted fabrication of three electrolysis cell types and performing parametric testing, off-design testing, and cell life testing. The Phase 2 consisted of the preliminary design, incorporation of palladium (Pd) tubes for hydrogen separation from the electrolyzer cathode feed gases, design support testing, final design, fabrication, and performance testing of the breadboard system. The results of performance tests demonstrated that CO2 electrolysis in an oxygen reclamation system for long duration space-based habitats is feasible. Closure of the oxygen system loop, therefore, can be achieved by CO2 electrolysis. In a two step process the metabolic CO2 and H2O vapor are electrolyzed into O2, H2, and CO. The CO can subsequently be disproportionated into carbon and CO2 in a carbon deposition reactor and the CO2 in turn be recycled and electrolyzed for total O2 recovery. The development effort demonstrated electrolyzer system can be designed and built to operate safely and reliably and the incorporation of Pd tubes for hydrogen diffusion can be integrated safely with predictable performance.

Isenberg, Arnold O.↗
NASA NTRS1990

Navier-Stokes analysis of transonic cascade flow

A new kind of C-type grid is proposed, this grid is non-periodic on the wake and allows minimum skewness for cascades with high turning and large camber. Reynolds-averaged Navier-Stokes equations are solved on this type of grid using a finite volume discretization and a full multigrid method which uses Runge-Kutta stepping as the driving scheme. The Baldwin-Lomax eddy-viscosity model is used for turbulence closure. A detailed numerical study is proposed for a highly loaded transonic blade. A grid independence analysis is presented in terms of pressure distribution, exit flow angles, and loss coefficient. Comparison with experiments clearly demonstrates the capability of the proposed procedure.

Arnone, A.↗
NASA NTRS1990

ZIP3D: An elastic and elastic-plastic finite-element analysis program for cracked bodies

ZIP3D is an elastic and an elastic-plastic finite element program to analyze cracks in three dimensional solids. The program may also be used to analyze uncracked bodies or multi-body problems involving contacting surfaces. For crack problems, the program has several unique features including the calculation of mixed-mode strain energy release rates using the three dimensional virtual crack closure technique, the calculation of the J integral using the equivalent domain integral method, the capability to extend the crack front under monotonic or cyclic loading, and the capability to close or open the crack surfaces during cyclic loading. The theories behind the various aspects of the program are explained briefly. Line-by-line data preparation is presented. Input data and results for an elastic analysis of a surface crack in a plate and for an elastic-plastic analysis of a single-edge-crack-tension specimen are also presented.

Shivakumar, K. N.↗
NASA NTRS1990

Turbulence modeling for high speed compressible flows

Turbulence models are necessary in numerical simulations because of the impracticality of computing all scales of turbulent motion. Approximate methods, or turbulence models, are introduced to simplify and make the computations practical. There are several approaches to turbulence modeling: subgrid scale modeling; modeling of all the scales of turbulent motion; eddy viscosity; and Reynolds stress turbulence closure models. In many instances, computations based on turbulence models are compared with available experimental data. The effort is directed at seeking models which have reasonable accuracy over a limited range of flow conditions. Future needs are briefly discussed. Work to date is outlined.

Chandra, Suresh↗
NASA NTRS1990

A comparison of fatigue life prediction methodologies for rotorcraft

Because of the current U.S. Army requirement that all new rotorcraft be designed to a 'six nines' reliability on fatigue life, this study was undertaken to assess the accuracy of the current safe life philosophy using the nominal stress Palmgrem-Miner linear cumulative damage rule to predict the fatigue life of rotorcraft dynamic components. It has been shown that this methodology can predict fatigue lives that differ from test lives by more than two orders of magnitude. A further objective of this work was to compare the accuracy of this methodology to another safe life method called the local strain approach as well as to a method which predicts fatigue life based solely on crack growth data. Spectrum fatigue tests were run on notched (k(sub t) = 3.2) specimens made of 4340 steel using the Felix/28 tests fairly well, being slightly on the unconservative side of the test data. The crack growth method, which is based on 'small crack' crack growth data and a crack-closure model, also predicted the fatigue lives very well with the predicted lives being slightly longer that the mean test lives but within the experimental scatter band. The crack growth model was also able to predict the change in test lives produced by the rainflow reconstructed spectra.

Everett, R. A., Jr.↗
NASA NTRS1990

Laboratory experiments on current flow between stationary and moving electrodes in magnetoplasmas

Laboratory experiments were performed in order to investigate the basic physics of current flow between tethered electrodes in magnetoplasmas. The major findings are summarized. The experiments are performed in an effectively very large laboratory plasma in which not only the nonlinear current collection is addressed but also the propagation and spread of currents, the formation of current wings by moving electrodes, the current closure, and radiation from transmission lines. The laboratory plasma consists of a pulsed dc discharge whose Maxwellian afterglow provides a quiescent, current-free uniform background plasma. Electrodes consisting of collectors and electron emitters are inserted into the plasma and a pulsed voltage is applied between two floating electrodes via insulated transmission lines. Besides the applied current in the wire, the total current density in the plasma is obtained from space and time resolved magnetic probe measurements via Maxwell's law. Langmuir probes yield the plasma parameters.

Stenzel, Reiner L.↗
NASA NTRS1991

Method for optimal configuration of an ECLSS on the Space Station Freedom

The establishment of a permanently manned Space Station represents a substantial challenge in the design of a life support system, specifically in the need to supply a large crew for missions of extended duration. The Space Station will evolve by time phased modular increments delivered and supplied by the Space Shuttle and other advanced launch systems. With the addition of each subsequent phase or alteration of mission duties, the requirements of the Station may differ from previous phases of development. With the addition of future crews and pressurized volume throughout the lifetime of the Space Station, change-out of individual subsystems may be necessary in order to meet the performance, safety, and reliability levels required from the Environmental Control and Life Support System (ECLSS). The analysis of this system growth demands the capability for advanced, integrated assessment techniques so that the unique mission drivers during each phase and mission scenario may be identified and evaluated. In order to determine the impacts of the interdependency between the ECLSS, the crew, the various user experiments, and the other distributed systems, consideration must be given to all Space Station resources and requirements during the initial and subsequent evolution phase. Therefore, it is necessary for analysis efforts to study the long term effects of established designs. These studies must quantify the optimal degree of loop closure within the capabilities of existing and future technologies including any resulting maintenance and logistics requirements. In addition, the necessity for subsystem retrofit during the lifetime of the Station must be examined. The source of system requirements due to long term exposure to the microgravity environment is illustrated, the criticality of the ECLSS functions is reviewed, and a method is described to develop an optimal design during each configuration based on the cross-consumption of Station resources. A comparison utilizing this procedure is discussed.

Gould, Marston J.↗