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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Centrally-Rupturing Squib-Closure Disks

Rupture-disk design makes squib action more predictable. In new design, center of rupture disk contains cruciform indentation in which thickness reduced to about 0.5 mil (0.013 mm). Reduces strength of center of rupture disk in same manner as that of pull tabs on beverage cans; therefore, disk will fail predictably in center.

Richter, R.↗
NASA NTRS1985

Galaxy luminosity functions, M/L ratios, and closure of the Universe - Numbers and problems

Data on the luminosity function (LF) of galaxies are reviewed and compared, and the result of Kirshner et al. (1983) giving a 'standard LF' is chosen as a best guess. Departures from the 'standard LF' for specific galaxy types and environments (clusters, groups, field) are discussed briefly. A luminosity density of about 1.4 x 10 to the -2nd h 'galaxies' per cubic megaparsec is obtained. The mean M/L ratio needed to give critical cosmological density (Omega sub 0 = 1) is then 920 h in solar units on the face-on magnitude system. Comparison with measured M/L ratios for galaxies and clusters, and with constraints imposed by inflation and nucleosynthesis, poses two problems of 'invisible mass'.

Felten, J. E.↗
NASA NTRS1985

Closure measurements on short fatigue cracks

Single-edged notched specimens, 2.3 mm thick, of 2024-T3 aluminum were cyclicly loaded at R-ratios of 0.5, 0.0, -1.0 and -2.0. The notch roots were periodically inspected with an optical microscope to locate the initiation of very short cracks. Acetate replicas were also taken. The loads were selected to produce fatigue lives of 500,000 cycles or less. Crack opening displacements were measured at single positions across cracks as short as 0.035 mm and as long as the full thickness of the specimen. The opening load ratios for the short cracks are somewhat smaller than for long cracks at positive R-ratios, but are considerably smaller for negative R-ratios.

Lee, J. J.↗
NASA NTRS1987

Closure models of turbulent third-order momentum and temperature fluctuations

A study is made for the development and computations of the separating and reattaching shear flows. The highlight of the study is an attempt to predict the third-moments of turbulent velocity which is responsible for the diffusion transport of the Reynolds stresses. The present computations show that the third-moments obtained by employing the law-Reynolds number model of transport equations improve the prediction of the third-moments. The modelling for scalar variables is also performed for the heat transfer computations. Since the transport equations for (u sub j theta)* and (u sub i u sub j theta) have been given in the last NASA CR, the study has been extended further to the modeling of (theta sup 2), (u sub i theta sup 2) and epsilon sub theta (dissipation rate of (theta sup 2)). The formulations are shown in this report.

Amano, R. S.↗
NASA NTRS1987

Computation of turbulent flows using an extended k-epsilon turbulence closure model

An extended kappa-epsilon turbulence model is proposed and tested with successful results. An improved transport equation for the rate of dissipation of the turbulent kinetic energy, epsilon, is proposed. The proposed model gives more effective response to the energy production rate than does the standard kappa-epsilon turbulence model. An extra time scale of the production range is included in the dissipation rate equation. This enables the present model to perform equally well for several turbulent flows with different characteristics, e.g., plane and axisymmetric jets, turbulent boundary layer flow, turbulent flow over a backward-facing step, and a confined turbulent swirling flow. A second-order accurate finite difference boundary layer code and a nearly second-order accurate finite difference elliptic flow solver are used for the present numerical computations.

Chen, Y.-S.↗
NASA NTRS1987

An experimental study of closure behavior of naturally initiated small cracks

Small cracks were initiated on the edges of 2024-T3 aluminum specimens by fatigue loading with various R-ratios. The crack opening displacement was then measured with a laser based interferometric technique and used to determine the operating load ratio. This ratio decreased with increasing distance from the tip. However, it remained essentially constant as the crack grew if a constant measuring system was used.

Su, X.↗
NASA NTRS1986

Closure in turbulence theory using stabilization principle

The approach presented is based upon the concept that the velocity fluctuations driven by the instability of the original flow grow until a new stable state is approached. The application of this stabilization principle is demonstrated by describing the smoothing out of a velocity discontinuity.

Zak, Michail↗
NASA NTRS1987

Investigation of third-order closure model of turbulence for the computation of incompressible flows in a channel with a backward-facing step

To predict the diffusion process of the Reynolds stresses in reattaching shear flows, the transport model for the triple-velocity products has been developed and tested for the computation of the flow in a channel with a backward-facing step. Upon comparison of the results of uuv, uvv, and vvv with those obtained by using existing algebraic correlations, it was shown that the present model improved the prediction of the triple-velocity products.

Amano, R. S.↗
NASA NTRS1988

The dependence of crack closure on fatigue loading variables

Optical and electron microscopy and stereoimaging techniques are used to determine crack opening loads local to the crack tip in aluminum alloy 7091 and 304 stainless steel. It is found that the crack peels open nonlinearly such that significant load increases are necessary to open the crack the last few microns from the tip. The stress intensity range ratio is shown to depend on fatigue loading variables according to a given relationship.

Hudak, Stephen J., Jr.↗
NASA NTRS1988

Closure measurements on short fatigue cracks

Single-edged notched specimens, 2.3 mm thick, of 2024-T3 aluminum were cyclically loaded at R-ratios of 0.5, 0.0, -1.0, and -2.0. The notch roots were periodically inspected with an optical microscope to locate the initiation of very short cracks. Acetate replicas were also taken. The loads were selected to produce fatigue lives of 500,000 cycles or less. Crack opening displacements were measured at single positions across cracks as short as 0.035 mm and as long as the full thickness of the specimen. The opening load ratios for the short cracks are somewhat smaller than for long cracks at positive R-ratios, but are considerably smaller for negative R-ratios.

Lee, Joo-Jin↗
NASA NTRS1988

An experimental study of the closure behavior of short and long cracks

Experiments were conducted on 2024-T3 aluminum specimens. The laser-based interferometric strain/displacement optical system was used to measure crack opening displacement. The displacement data were measured near the crack tip, at the crack mouth, and at other locations along the crack line for both short and long cracks. The dependence of opening load ratio on measurement locations was observed. The ratio decreased systematically as the measurement locations moved away from the crack tip. However, the ratio stayed roughly the same for the near tip surface measurements at various crack lengths.

Su, X.↗
NASA NTRS1988

A closure model of diffusion transport of the Reynolds-stress equations and its application to a turbulent step flow

A study is made for the development and computations of the separating and reattaching shear flows. The highlight of the study is an attempt to predict the third-moments of turbulent velocity which is responsible for the diffusion transport of the Reynolds stresses. The present computations show that the third-moments obtained by employing the low-Reynolds number model of transport equations improve the prediction of the third-moments.

Amano, R. S.↗
NASA NTRS1989

Closure of field-aligned currents carried by super-Alfvenic auroral electrons

A linear analysis is carried out to investigate how the return current is generated for the field-aligned current carried by a super-Alfvenic auroral electron beam. If the electron beam is a thin sheet with thickness less than or equal to the electron inertia length, the negative space charge of the beam is neutralized by the ion polarization current produced by the beam. The return current in this case is generated on the two outsides of the beam connected to the polarization current to form a closed current loop. This current structure can explain the thin (a few km) current sheets in the auroral arcs observed by satellites.

Nakamura, Tadas↗