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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Cellular automatons applied to gas dynamic problems

This paper compares the results of a relatively new computational fluid dynamics method, cellular automatons, with experimental data and analytical results. This technique has been shown to qualitatively predict fluidlike behavior; however, there have been few published comparisons with experiment or other theories. Comparisons are made for a one-dimensional supersonic piston problem, Stokes first problem, and the flow past a normal flat plate. These comparisons are used to assess the ability of the method to accurately model fluid dynamic behavior and to point out its limitations. Reasonable results were obtained for all three test cases, but the fundamental limitations of cellular automatons are numerous. It may be misleading, at this time, to say that cellular automatons are a computationally efficient technique. Other methods, based on continuum or kinetic theory, would also be very efficient if as little of the physics were included.

Long, Lyle N.↗
NASA NTRS1992

Grain size reduction in granular flows of spheres - The effects of critical impact energy

Methods employed to derive recent kinetic theories for rapid noncomminuting granular flows are extended to homogeneous flows in which a fraction of the repeated collisions produce tiny fractures on the particles' peripheries and gradually reduce their effective diameters. The theory consists of balance equations for mass, momentum, and energy, as well as constitutive relations for the presence tensor and collisional rates of mass and energy lost. The work of Richman and Chou (1989) is improved by incorporating into the constitutive theory the critical impact energy below which no mass loss occurs in a binary collision. The theory is applied to granular shear flows and, for fixed shear rates, predicts the time variations of the solid fraction granular temperature, and induced stresses, as well as their extreme sensitivities to small changes in the critical impact energy.

Richman, M. W.↗
NASA NTRS1995

Simulating the interaction of the heliosphere with the local interstellar medium: MHD results from a finite volume approach, first bidimensional results

We have designed a full compressible MHD code working on unstructured meshes in order to be able to compute accurately sharp structures embedded in large scale simulations. The code is based on a finite volume method making use of a kinetic flux splitting. A bidimensional version of the code has been used to simulate the interaction of a moving interstellar medium, magnetized or unmagnetized with a rotating and magnetized heliopspheric plasma source. Being aware that these computations are not realistic due to the restriction to two dimensions, we present it to demonstrate the ability of this new code to handle this problem. An axisymetric version, now under development, will be operational in a few months. Ultimately we plan to run a full 3d version.

Chanteur, G.↗
NASA NTRS1996

Propellant Chemistry for CFD Applications

Current concepts for reusable launch vehicle design have created renewed interest in the use of RP-1 fuels for high pressure and tri-propellant propulsion systems. Such designs require the use of an analytical technology that accurately accounts for the effects of real fluid properties, combustion of large hydrocarbon fuel modules, and the possibility of soot formation. These effects are inadequately treated in current computational fluid dynamic (CFD) codes used for propulsion system analyses. The objective of this investigation is to provide an accurate analytical description of hydrocarbon combustion thermodynamics and kinetics that is sufficiently computationally efficient to be a practical design tool when used with CFD codes such as the FDNS code. A rigorous description of real fluid properties for RP-1 and its combustion products will be derived from the literature and from experiments conducted in this investigation. Upon the establishment of such a description, the fluid description will be simplified by using the minimum of empiricism necessary to maintain accurate combustion analyses and including such empirical models into an appropriate CFD code. An additional benefit of this approach is that the real fluid properties analysis simplifies the introduction of the effects of droplet sprays into the combustion model. Typical species compositions of RP-1 have been identified, surrogate fuels have been established for analyses, and combustion and sooting reaction kinetics models have been developed. Methods for predicting the necessary real fluid properties have been developed and essential experiments have been designed. Verification studies are in progress, and preliminary results from these studies will be presented. The approach has been determined to be feasible, and upon its completion the required methodology for accurate performance and heat transfer CFD analyses for high pressure, tri-propellant propulsion systems will be available.

Farmer, R. C.↗
NASA NTRS1996

Excitation of Plasma Waves in Aurora by Electron Beams

In this paper, we study numerically the excitation of plasma waves by electron beams, in the auroral region above 2000 km of altitude. We have solved the fully kinetic dispersion relation, using numerical method and found the real frequency and the growth rate of the plasma wave modes. We have examined the instability properties of low-frequency waves such as the Electromagnetic Ion Cyclotron (EMIC) wave as well as Lower-Hybrid (LH) wave in the range of high-frequency. In all cases, the source of free energy are electron beams propagating parallel to the geomagnetic field. We present some features of the growth rate modes, when the cold plasma parameters are changed, such as background electrons and ions species (H(+) and O(+)) temperature, density or the electron beam density and/or drift velocity. These results can be used in a test-particle simulation code, to investigate the ion acceleration and their implication in the auroral acceleration processes, by wave-particle interaction.

daSilva, C. E.↗
NASA NTRS2002

Non-Rocket Earth-Moon Transport System

This paper proposes a new method and transportation system to travel to the Moon. This transportation system uses a mechanical energy transfer and requires only minimal energy so that it provides a 'Free Trip' into space. The method uses the rotary and kinetic energy of the Moon. This paper presents the theory and results of computations for the project provided Free Trips (without rockets and spend a big energy) to the Moon for six thousand people annually. The project uses artificial materials like nanotubes and whiskers that have a ratio of tensile strength to density equal 4 million meters. In the future, nanotubes will be produced that can reach a specific stress up 100 millions meter and will significantly improve the parameters of suggested project. The author is prepared to discuss the problems with serious organizations that want to research and develop these innovations.

Bolonkin, Alexander↗
NASA NTRS1997

Cytogenetic effects of space radiation in lymphocytes of MIR-18 crews

For assessing health risk, the measurement of physical dose received during a space mission, as well as the LETs, energies and charges of particles is important. It is also important to obtain quantitative information regarding the effectiveness of space radiation in causing damage to critical biological targets, e.g., chromosomes, since at present the estimated uncertainty of biological effects of space radiation is more than a factor of two. Such large uncertainty makes accurate health risk assessment very difficult. For this very reason, a study on cytogenetic effects of space radiation in human lymphocytes was proposed and done for MIR-18 mission. This study used FISH technique to score chromosomal translocations and C-banding method to determine dicentrics. Growth kinetics of cells and SCE were examined to ensure that chromosomal aberrations were scored in first mitosis and were induced not by chemical mutagens. Our results showed that chromosomal aberration frequency of post-flight samples was significantly higher than that of pre-flight ones and that SCE frequency was similar between pre- and post-flight samples. Based on a dose-response curve of preflight samples exposed to gamma rays, the absorbed dose received by crews during the mission was estimated to be about 14.5 cSv. Because the absorbed dose measured by physical dosimeters is 4.16 cGy for the entire mission, the RBE is about 3.5.

Mir Project↗
NASA NTRS2018

Collisionless Relaxation of the Ion Ring Distribution in Space Plasma

Energetic processes often produce transversely-heated angular distributions of the magnetized core (lowest energy) plasma. This characteristic is found in solar wind ion pickup, resulting from cometary or interstellar gas ionization, in Earths' ionosphere, and with hot ions formed around the Space Transportation System during gas releases. We investigate the thermalization of O+ ion pickup using the 2.5D hybrid simulation method (with fluid electrons and kinetic ions) of the ion pickup (ring) distributions, formed in the auroral ionosphere, with a range of ring velocities and thermal to magnetic pressure ratios. We find that in the unstable collisonless regime the anisotropy of the non-thermal distribution produces the ion-cyclotron instability, and the nonlinear relaxation is accompanied by wave-particle scattering that results in an emitted power of EMIC waves. We conclude that ionospheric pickup thermalization is slow due to the small ring speed compared to the thermal and Alfven speeds, while in the solar wind and other space plasmas regions with larger ion-ring velocity the collisionless relaxation and thermalization is rapid in terms of O+ ion gyro-period.

Ofman, Leon↗
NASA NTRSDate not supplied

Determination of Interfacial Energy for Solid-State Precipitation

Precipitation of strengthening phases from solid state is a critical process for many materials. For example, the high-temperature creep resistance of Ni-based superalloys is governed by ’ precipitates. However, the interfacial energy which controls the precipitation is expensive to determine experimentally. For simulations, the atomic nature of precipitation events necessitates using Molecular Dynamics (MD) so relying on fitting to a-priori experimental behavior is not required. However, the solid-state precipitation takes orders of magnitude longer time than is accessible for traditional MD simulation. Taking inspiration from Kinetic Monte-Carlo (KMC) methods for simulating diffusion on a rigid lattice, we have developed a hybrid KMC-MD approach to enable simulation of solid-state precipitation (and determination of the interfacial energy). Implementing these methods in LAMMPS, we calculated the interfacial energy for the ’ precipitation out of a super-saturated  phase in Ni-based superalloys. The resulting interfacial energy value for the Ni-Al system is well within the accuracy of experimental values, demonstrating the capability of this method. Enabling the calculation of the interfacial energy without a-priori experimental knowledge of the precipitation unlocks a more efficient ICME-based approach for guiding annealing protocols in Ni-based superalloys and other solid-state precipitation systems.

Precipitation↗
NASA NTRS1978

Collisional excitation of interstellar molecules - Linear molecules CO, CS, OCS, and HC3N

Rates for excitation of CO, CS, OCS, and HC3N by collisions with He atoms and H2 molecules are presented. These have been obtained from extensive theoretical calculations using methods of known reliability. In general, rates necessary for modeling interstellar molecular clouds with kinetic temperatures to 100 K have been included. Methods for fitting these rates in more compact form are discussed.

Green, S.↗
NASA NTRS1988

Kinetics of thermochemical gas-solid reactions important in the Venus sulfur cycle

The thermochemical net reaction CaCO3 + SO2 yields CaSO4 + CO is predicted to be an important sink for incorporation of SO2 into the Venus crust. The reaction rate law was established to understand the dependence of rate on experimental variables such as temperature and partial pressure of SO2, CO2, and O2. The experimental approach was a variant of the thermogravimetric method often employed to study the kinetics of thermochemical gas-solid reactions. Clear calcite crystals were heated at constant temperature in SO2-bearing gas streams for varying time periods. Reaction rate was determined by three independent methods. A weighted linear least squares fit to all rate data yielded a rate equation. Based on the Venera 13, 14 and Vega 2 observations of CaO content of the Venus atmosphere, SO2 at the calculated rate would be removed from the Venus atmosphere in about 1,900,00 years. The most plausible endogenic source of the sulfur needed to replenish atmospheric SO2 is volcanism. The annual amount of erupted material needed for the replenishment depends on sulfur content; three ratios are used to calculate rates ranging from 0.4 to 11 cu km/year. This geochemically derived volcanism rate can be used to test if geophysically derived rates are correct. The work also suggests that Venus is less volcanically active than the Earth.

Fegley, Bruce, Jr.↗
NASA NTRS1989

Time-resolved simplified chemical kinetics modelling using computational singular perturbation

A CO-CH4-air reaction system is used to demonstrate the computational singular perturbation (CSP) method for deriving time-resolved simplified chemical kinetics models. CSP provides a programmable algorithm to group the given collection of elementary reactions into reaction groups which are ordered according to their speed. The concept of Importance Index k(m)exp s is introduced: k(m)exp s is defined to be a number between 0 and 1 which measures the importance of the m-th reaction group to the s-th reactant and can readily be computed from data generated by CSP. It is suggested that the robustness of the solutions of the reaction system can be qualitatively assessed by inspecting the Importance Index data.

Lam, S. H.↗
NASA NTRS2023

Chemical Thermodynamics and the Mathematical Integration of Reaction Kinetics

Key advances in the development of numerical methods for non-reacting compressible flows have been enabled by translating physical requirements into concrete numerical guidelines, such as the satisfaction of entropy inequalities for shock-capturing techniques [Lax, Contributions to Nonlinear Functional Analysis (1971) 603-634]. In the present work, we present nonlinear numerical analysis tools that draw from Chemical Thermodynamics , the branch of Nonequilibrium Thermodynamics that deals with chemical reactions. Through Gibbs formalism, chemical thermodynamics provides a well-known theoretical expression for the chemical equilibrium constant of a reaction in terms of reduced chemical potentials. A less-known, yet extremely valuable result, due to [Krambeck, Arch. Ration. Mech. Anal. , 38 (1970) 317], states that when this expression is implemented, mass-action kinetic models are consistent with the dynamical prescriptions of the 2nd law of thermodynamics. For fixed-temperature ordinary differential equations modeling constant-volume reacting gas mixtures, this leads to a decreasing Helmholtz free energy. If the temperature is allowed to vary in accordance with conservation of energy (1st law), this leads to the statement of increasing entropy. These nonlinear prescriptions can, and should be, used to further develop temporal integration techniques for reaction kinetics. We demonstrate that Krambeck's result holds even when the equilibrium constants are approximated from data. We prove this result by constructing the implicit free energy and the implicit entropy inherent to a given approximation. This is first done for a 5-species, 17-reaction model problem for air. With this structure established, elements of discrete entropy-stability theory [Tadmor, Acta Numer. , 12 (2003) 451] are leveraged to examine the consistency of time-integration schemes with these prescriptions. Using chemical potentials, one can compute the respective contributions of the kinetics model and of the temporal scheme to free energy/entropy variations. We introduce a nonlinear-stable version of the Discontinuous-Galerkin (DG) scheme in time which shows robustness improvements over the standard linearly-stable version. Most notably, the maximum timestep that can be resolved with the nonlinearly-stable variant tends to grow with polynomial order, in contrast to the linearly-stable variant. We generalize our constructions to arbitrary systems of reversible chemical reactions, ultimately showing that the compressible reacting Euler system admits the opposite of the implicitly constructed thermodynamic entropy as a mathematical entropy . This lays important theoretical foundations towards robust scheme development [Harten, J. Comput. Phys. 49 (1983) 151-164].

STMD↗
NASA NTRS1992

Recovery and separation of precious metals from space

During the past year a viable procedure centered around centrifugal partition chromatography (CPC), a multistage liquid-liquid partitioning technique for the separation of precious metals (Pt, Pd, Rh, Ir, Os, Ru), was developed. Stable and inexpensive ligands that can be readily recycled to achieve the separations of the precious metals were identified. The separation methods developed so far yield three separate fractions: Pt, Pd, and Rh-Ir. The Rh-Ir pair can be separated in a subsequent run. The total amount of precious metals separated in a single experiment varied from 1 to 50 mg. The factors affecting the efficiencies of these separations were studied. The kinetics of the decomposition of the complex and the ion pair have a major bearing on these efficiencies, with slow kinetics resulting in poor efficiencies. The methods for the improvement of the efficiencies were also investigated. For example, significant improvement in the efficiencies and separation times for Pt and Pd were achieved by the use of chloride gradient in the mobile phase. Two papers were published and talks were presented on our work at the FACSS meeting in Anaheim, Oct. 1991, and at the Pittsburgh Conference in New Orleans, Mar. 1992.

Freiser, H.↗
NASA NTRS1986

A method for screening of plant species for space use

A cost-effective methodology which monitors numerous dynamic aspects of carbon assimilation and allocation kinetics in live, intact plants is discussed. Analogous methods can apply to nitrogen uptake and allocation. This methodology capitalizes on the special properties of the short-lived, positron-gamma emitting isotope C-11 especially when applied as CO2-11 in a special extended square wave (ESW) pattern. The 20.4 minute half-life allows for repeated or continuous experiments on the same plant over periods of minutes, hours, days, or weeks. The steady-state isotope equilibrium approached during the ESW experiments, and the parameters which can be analyzed by this technique are also direct results of that short half-life. Additionally, the paired .511 MeV gamma rays penetrate any amount of tissue and their 180 deg opposite orientation provides good collimation and allows coincidence counting which nearly eliminates background.

Goeschl, J. D.↗
NASA NTRS1997

Automated Simplification of Full Chemical Mechanisms

A code has been developed to automatically simplify full chemical mechanisms. The method employed is based on the Intrinsic Low Dimensional Manifold (ILDM) method of Maas and Pope. The ILDM method is a dynamical systems approach to the simplification of large chemical kinetic mechanisms. By identifying low-dimensional attracting manifolds, the method allows complex full mechanisms to be parameterized by just a few variables; in effect, generating reduced chemical mechanisms by an automatic procedure. These resulting mechanisms however, still retain all the species used in the full mechanism. Full and skeletal mechanisms for various fuels are simplified to a two dimensional manifold, and the resulting mechanisms are found to compare well with the full mechanisms, and show significant improvement over global one step mechanisms, such as those by Westbrook and Dryer. In addition, by using an ILDM reaction mechanism in a CID code, a considerable improvement in turn-around time can be achieved.

Norris, A. T.↗
NASA NTRS1997

Application of Low Dimensional Manifolds in NO(x) Prediction

A new post-processing technique has been developed, based on the Intrinsic Low Dimensional Manifold (ILDM) method of Maas and Pope. The ILDM method is a dynamical systems approach to the simplification of large chemical kinetic mechanisms. By identifying low-dimensional attracting manifolds, the method allows complex full mechanisms to be parameterized by just a few variables: In effect, generating reduced chemical mechanisms by an automatic procedure. These resulting mechanisms however, still retain all the species used in the full mechanism. The NO(x) post-processor takes an ILDM reduced mechanism and attempts to map this mechanism to the results of a CFD calculation. This mapping allows the NO(x) concentrations at each grid node to be obtained from the ILDM reduced mechanism, as well as other trace species of interest. Because a mapping procedure is used, this method is very fast, being able to process one million node calculations in just a few minutes.

Norris, A. T.↗