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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Advanced low NO/x/ combustors for supersonic high-altitude aircraft gas turbines

A test rig program was conducted with the objective of evaluating and minimizing the exhaust emissions, in particular NO(x), of two advanced aircraft combustor concepts at a simulated, high-altitude cruise condition. The two combustor designs, both members of the lean-reaction, pre-mixed family, are known as the Jet Induced Circulation (JIC) combustor and the Vortex Air Blast (VAB) combustor and were rig tested in the form of reverse flow can combustors in the 0.127-m size range. Various configuration modifications were applied to each of the initial JIC and VAB combustor model designs in an effort to reduce the emissions levels. The VAB combustor demonstrated a NO(x) level of 1.1 gm NO2/kg fuel with essentially 100 percent combustion efficiency at the simulated cruise combustor condition of 507 kPa, 833 K inlet pressure and temperature, respectively and 1778 K outlet temperature on Jet-A1 fuel. In addition, emissions data were obtained at low combustor inlet pressure and temperatures that indicate the potential performance at engine off-design conditions.

Roberts, P. B.↗
NASA NTRS1977

Gaseous-fuel nuclear reactor research for multimegawatt power in space

In the gaseous-fuel reactor concept, the fissile material is contained in a moderator-reflector cavity and exists in the form of a flowing gas or plasma separated from the cavity walls by means of fluid mechanical forces. Temperatures in excess of structural limitations are possible for low-specific-mass power and high-specific-impulse propulsion in space. Experiments have been conducted with a canister filled with enriched UF6 inserted into a beryllium-reflected cavity. A theoretically predicted critical mass of 6 kg was measured. The UF6 was also circulated through this cavity, demonstrating stable reactor operation with the fuel in motion. Because the flowing gaseous fuel can be continuously processed, the radioactive waste in this type of reactor can be kept small. Another potential of fissioning gases is the possibility of converting the kinetic energy of fission fragments directly into coherent electromagnetic radiation, the nuclear pumping of lasers. Numerous nuclear laser experiments indicate the possibility of transmitting power in space directly from fission energy. The estimated specific mass of a multimegawatt gaseous-fuel reactor power system is from 1 to 5 kg/kW while the companion laser-power receiver station would be much lower in specific mass.

Thom, K.↗
NASA NTRS1978

Paleohydraulics and hydrodynamics of Scabland floods

The last major episode of scabland flooding (approx. 18,000-13,000 years B.P.) left considerable high-water mark evidence in the form of: (1) eroded channel margins; (2) depositional features; (3) ice-rafter erratics; and (4) divide crossings. These were used to reconstruct maximum flood stages and water-surface gradients. Engineering hydraulic calculation procedures allowed the analyses of flood discharges and mean velocities from these data. Secondary flow phenomena, including various forms of vortices and flow separations, are considered to have been the principal erosive processes. The intense pressure and velocity gradients of vortices along the irregular channel boundaries produced the plucking-type erosion.

Baker, V. R.↗
NASA NTRS1979

Radiative amplification of sound waves in the winds of O and B stars

The velocity perturbation associated with an outwardly propagating sound wave in a radiation-driven stellar wind gives rise to a periodic Doppler shifting of absorption lines formed in the flow. A linearized theory applicable to optically thin waves is used to show that the resulting fluctuation in the absorption-line force can cause the wave amplitude to grow. Detailed calculations of the acceleration due to a large number of lines indicate that significant amplification can occur throughout the high-velocity portion of winds in which the dominant force-producing lines have appreciable optical depths. In the particular case of the wind of Zeta Pup (O4f), it is found that the e-folding distance for wave growth is considerably shorter than the scale lengths over which the physical properties of the flow vary. A qualitative estimate of the rate at which mechanical energy due to nonlinear waves can be dissipated suggests that this mechanism may be important in heating the supersonic portion of winds of early-type stars.

Macgregor, K. B.↗
NASA NTRS1980

Driver gas flow with fluctuations

A shock tube's driver gas can apparently provide flow with turbulent bursts. The fluctuations are interpreted using a boundary layer model of contact surface flow and results form a kinetic theory of turbulence. With this, a lower limit of 4 on the ratio of maximum to minimum turbulent intensities in contact surface instabilities has been estimated.

Johnson, J. A., III↗
NASA NTRS1982

New Method For Joining Stainless Steel to Titanium

In new process, edge of stainless-steel sheet is perforated, and joined to titanium by resistance seam welding. Titanium flows into perforations, forming a strong interlocking joint. Process creates a quasi-metallurgical bond between the thin sheets of stainless steel and titanium.

Emanuel, W. H.↗
NASA NTRS1981

Navier-Stokes solutions for nonaxisymmetric nozzle flows

The compressible Navier-Stokes equations for two-dimensional and three-dimensional flow are solved for nonaxisymmetric nozzle configurations. Both internal flow alone and combined internal and external flow cases are considered. An implicit approximate factorization algorithm is employed to solve the governing equations which are cast in terms of a body-fitted coordinate system. Turbulence closure is accomplished with a composite algebraic model. Two-dimensional results for a wedge plug nozzle flow in the form of surface pressures compare favorably with experimental data. Three-dimensional calculations for two nonaxisymmetric nozzles are also presented and compared with data.

Swanson, R. C.↗
NASA NTRS1982

Laser Doppler measurements of laminar and turbulent flow in a pipe bend

The streamwise components of velocity in the flow through a ninety degree bend of circular cross section for which the ratio of radius of curvature to diameter is 2.8 were measured. The development of strong pressure driven secondary flow in the form of a pair of counter rotating vortices in the steamwise direction is shown. Refractive index matching at the fluid wall interface was not employed; the displacement of the measurement volume due to refraction is allowed for in simple geometrical calculations.

Enayet, M. M.↗
NASA NTRS1983

Geochemistry of volcanic rocks from the Wawa greenstone belt

The Wawa greenstone belt is located in the District of Algoma and extends east-northeast from Lake Superior to the western part of the Sudbury District in Ontario, Canada. Recent mapping by Attoh has shown that an unconformity at the base of the Dore' Formation and equivalent sedimentary rocks marks a significant stratigraphic break which can be traced throughout the volcanic belt. This break has been used to subdivide the volcanic-sedimentary into pre- and post-Dore' sequences. The pre-Dore' sequence includes at least two cycles of mafic-to-felsic volcanism, each capped by an iron-formation unit. The post-Dore' sequence includes an older mafic-to-felsic unit, which directly overlies sedimentary rocks correlated with the Dore' Formation, and a younger felsic breccia unit interpreted to have formed as debris flows from a felsic volcanic center. In the present study, samples of both the pre-and post-Dore' volcanic sequences were analyzed for major and trace elements, incuding rare earths (REE). This preliminary study is part of an ongoing program to assess the petrogenesis of the volcanic rocks of the Wawa greenstone belt.

Schulz, K. J.↗
NASA NTRS1985

Basaltic Pressure Ridges: Formation and Relationship to Flow Emplacement

Pressure ridges and pressure plateau are common but not ubiquitous surface features on terrestrial basaltic lava flows and may reflect a specific flow emplacement mechanism. Many of the ridges are large enough to be detected on high-resolution orbital images; therefore, understanding these features could provide a means for interpreting volcanic flows on the mechanism of pressure ridge formation and how their formation relates to flow emplacement. Results from detailed field studies indicate that pressure ridges and plateaus: (1) are emplaced as individual flow lobes, (2) can be composed of primary or secondary material, (3) are dependent on duration and volume of activity within the flow unit, (4) are penecontemporaneous in formation, and (5) are indicative of slowly advancing flows with numerous flow lobes continuously forming and overriding each other.

Theilig, E.↗
NASA NTRS1985

Catastrophic debris avalanche deposit of Socompa volcano, northern Chile

Between 10,000 and 500 yr ago the Socompa volcano in northern Chile experienced a catastrophic collapse of a 70 deg sector of the original cone, causing a debris avalanche that descended nearly 3000 m vertically and traveled more than 35 km from the volcano. The deposits cover some 490 sq km and have a minimum volume of 15 cu km. Parts of the original cone slumped in a nearly coherent form and are now preserved as large blocks more than 400 m high. The primary avalanche traveled northwestward over sloping ground before coming to rest transiently, forming a prominent marginal ridge, and then slid away northeastward to form a secondary flow, overriding much of the primary avalanche deposit. Abundant, prismatic, jointed dacite blocks within the debris avalanche deposit and a thin, fine-grained pumiceous deposit beneath it suggest that the collapse was triggered by magmatic activity and may have been accompanied by a violent lateral blast. Collapse was followed by eruption of pumiceous pyroclastic flows and extrusion of voluminous dacite domes.

Francis, P. W.↗
NASA NTRS1987

Effect of a localized minimum in equatorial field strength on resistive tearing instability in the geomagnetotail

A two-dimensional, resistive-MHD computer code is used to investigate the spontaneous reconnection of magnetotaillike configurations. The initial conditions adopted in the simulations are of two types: (1) in which the equatorial normal magnetic field component B(ze) declines monotonically down the tail, and (2) in which B(ze) exhibits a deep minimum in the near-earth plasma sheet. To represent the case where the earthward convection stops before the X line forms, zero-flow boundary conditions are imposed at the edges of the computational box. The initial configurations are in equilibrium and table within ideal MHD. The dynamic evolution of the system starts after the resistivity is turned on. The main results of these simulations basically support the neutral-line model of substorms and confirm Birn's (1980) computer studies. Spontaneous formation of an X-type neutral point and a single O-type plasmoid with strong tailward flow on the tailward side of the X point is found. The time interval from the turning on of the resistivity to the formation of a plasmoid is much shorter in the case where there is an initial deep minimum. A simple analytic calculation is also carried out to demonstrate why the configuration with a deep minimum is more susceptible to the development of the neutral point.

Hau, L.-N.↗
NASA NTRS1987

Weak solar fields and their connection to the solar cycle

Videomagnetograph observations of the weak solar magnetic fields are discussed. Intranetwork (IN) elements are found to emerge in bipolar form, but to flow in a random pattern rather than toward the network elements. Merging of IN fields is found to be more important than the ephemeral regions as a source of new network elements. Arguments for and against the hypothesis that all solar fields are intrinsically strong are considered. It is noted that reconnection and merging of magnetic fields take place continually under the conditions presently examined.

Zirin, Harold↗
NASA NTRS1987

Preconditioned methods for solving the incompressible and low speed compressible equations

The introduction of artificial time derivatives which permit faster convergence to the steady state is used to precondition steady state incompressible equation-solving acceleration methods. An optimal value is obtained for beta, given constant alpha, where alpha and beta are arbitrary functions in the general preconditioning stage. A symmetric hyperbolic system is formed by the resulting incompressible equations. Compressible equations in conservation form with slow flow are also considered.

Turkel, Eli↗
NASA NTRS1988

Phenomenological modeling of hardening and thermal recovery in metals

Modeling of hardening and thermal recovery in metals is considered within the context of unified elastic-viscoplastic theories. Specifically, the choices of internal variables and hardening measures, and the resulting hardening response obtained by incorporating saturation-type evolution equations into two general forms of the flow law are examined. Based on the analytical considerations, a procedure for delineating directional and isotropic hardening from uniaxial hardening data has been developed for the Bodner-Partom model and applied to a nickel-base superalloy, B1900 + Hf. Predictions based on the directional hardening properties deduced from the monotonic loading data are shown to be in good agreement with results of cyclic tests.

Chan, K. S.↗
NASA NTRS1987

Roosevelt County 027 - A low-shock ureilite with interstitial silicates and high noble gas concentrations

The RC027 lightly-shocked ureilite contains less than 1 percent of a fine-grained interstitial silicate that has an igneous texture indicating crystallization from an interstitial liquid. RC027 is also noted to exhibit the strongest olivine preferred-orientation thus far observed in a ureilite; its fabric is characteristic of fabrics formed by tabular minerals in a fluid laminar flow regime, and is unlike those formed by synectonic recrystallization and plastic flow. The elemental and isotopic compositions of noble gases in RC027 are typical of previously analyzed ureilites.

Goodrich, Cyrena Anne↗