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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

The effects on the MHD stability of field line tying to the end faces of a cylindrical magnetic loop

The ideal MHD energy equation is used to derive a stability equation for a specific class of perturbations, in an examination of magnetic loop MHD stability which takes field line tying at its root points into account. It is found that the field line tying effect is negligible to the m=1 kink mode, but important to the localized modes, in the case of a loop of aspect ratio greater than 10. The stability criterion for high-m value localized modes is derived, and compared with the Suydam criterion, to show that there are two field line tying effects for the perturbation of the class studied: (1) a field line bending effect, which is always stabilizing, and (2) a shear effect which is stabilizing or destabilizing depending on the sign of the gradient of the potential magnetic field. The net effect of field line tying is determined by the sum of these two effects.

An, C. Y.↗
NASA NTRS1982

Moonport to Spaceport - The changing face at KSC

The facilities and planned operations of the Orbiter Processing Facility (OPF) at Kennedy Space Center are described, noting an eventual goal of five to six weeks turnaround for the vehicle. The dual-bay OPF is being developed to handle processing of two Orbiters in parallel. Once in the facility, all fuels are drained, parts and systems needing maintenance are removed for shipping and refurbishing or repair in-place, hazardous cargo is secured, and a thorough visual inspection is made of all accessible areas. Mobile launch platforms previously used as transports in the Apollo program have been upgraded and modernized and serve for the Shuttle launch preparations. Details of launch procedures are outlined, and the reduction of launch personnel to 45 persons is mentioned. Finally, details of payload insertion and mating with the Spacelab modules are described, along with the progress on the test flights.

Boggs, W. H.↗
NASA NTRS1981

Hostile environmental conditions facing candidate alloys for the automotive Stirling engine

The materials research program in support of the Automotive Stirling Engine Project focuses on the hot heater head of the engine including the heater head tubes, cylinders, and regenerator housings, which are considered to be the most critical components from a materials viewpoint. The specific areas of investigation in the program involve hydrogen permeability testing, doping of the hydrogen working fluid to reduce permeability rates, oxidation/corrosion studies, creep-rupture evaluation, and assessing effects of hydrogen environment on mechanical properties. Emphasis is placed on the materials challenges that result from the use of hydrogen as the working fluid. Previously announced in STAR as N81-26236

Stephens, J. R.↗
NASA NTRS1984

Composites for large transports - Facing the challenge

NASA has undertaken development and test programs in collaboration with the large transport aircraft construction industry, in order to remove existing barriers to the use of composite material primary structures and to assess their advantages in terms of both acquisition cost and mission performance. These programs are expected to reach design technology readiness for wing and fuselage structures by 1988, paving the way for the validation of design and manufacturing methods in the early 1990s. While composites promise a reduction in fuselage manufacturing costs, it is judged that the relative cost of a metallic wing will be more difficult to surpass. Nevertheless, a 40 percent wing weight saving may more than compensate for increased wing structure cost.

Bohon, H. L.↗
NASA NTRS1984

The many faces of Capella - A search for rotational modulations and a study of systematic velocities of emission lines in the ultraviolet

The UV spectra of Capella were monitored for fluctuations using IUE instrumentation, and radial velocities of the emission lines were determined. The possible fluctuations were studied from March through April 1981, and radial velocity data were taken over six days in 1982. The Capella surface activity emissions proved to be steady, while redshifts from high excitation were found in the photospheric plasma. Downflows of 100,000 K plasma in the stellar transition zone could produce the redshifts. The FWHMs of the emission lines exceeded the redshift by an order of magnitude, suggesting that the observed excitations could be only averaged values of the dynamics of the outer atmosphere of Capella.

Ayres, T. R.↗
NASA NTRS1986

Variable friction secondary seal for face seals

Vibration and stability of a primary seal ring is controlled by a secondary seal system. An inflatable bladder which forms a portion of the secondary seal varies the damping applied to this seal ring. The amplitude of vibration of the primary seal ring is sensed with a proximity probe that is connected to a microprocessor in a control system. The bladder pressure is changed by the control system to mitigate any sensed instability or vibration.

Dirusso, E.↗
NASA NTRS1985

Numerical simulation of a turbulent flame stabilized behind a rearward-facing step

Flow of combustible mixtures in a plane channel past a smooth contraction followed by an abrupt expansion, in a typical dump combustor configuration, is modeled by a two-dimensional numerical technique based on the random vortex method. Both the inert and the reacting case are considered. In the latter, the flame is treated as an interface, self-advancing at a prescribed normal burning speed, while the dynamic effects of expansion due to the exothermicity of combustion are expressed by volumetric source lines delineated by its front. Solutions are shown to be in satisfactory agreement with experimental results, especially with respect to global properties such as the average velocity profiles and the reattachment length. The stochastic turbulent velocity components manifest interesting differences, especially near the walls where three-dimensional effects of turbulence are expected to be of importance.

Hsiao, C. C.↗
NASA NTRS1987

Three-dimensional numerical predictions of the flow behind a rearward-facing-step in a supersonic combustor

A CFD code was developed to compute the mixing and combustion of hydrogen fuel in the turbulent flow fields of scramjets. The code is based on the complete Reynold's time-averaged three-dimensional Navier-Stokes equations, and chemical species equations. The code includes a global finite rate hydrogen-air chemical reaction model and the Baldwin-Lomax (1978) turbulence model. The validity of this CFD code was demonstrated by comparing computed results from the code with existing data for three configurations, each containing an important feature of the scramjet combustor flow. The code was then applied to the reacting flow field in a complex combustor model in which hydrogen fuel was injected transversely into a supersonic hot airstream through several fuel injectors.

Uenishi, K.↗
NASA NTRS1988

Thermal effects in two-phase flow through face seals

When liquid is sealed at high temperature, it flashes inside the seal due to pressure drop and/or viscous heat dissipation. Two-phase seals generally exhibit more erratic behavior than their single phase counterparts. Thermal effects, which are often neglected in single phase seal analyses, play an important role in determining seal behavior under two-phase operation. It is necessary to consider the heat generation due to viscous shear, conduction into the seal rings and convection with the leakage flow. Analytical models developed work reasonably well at the two extremes - for low leakage rates when convection is neglected and for higher leakage rates when conduction is neglected. A preliminary model, known as the Film Coefficient Model, is presented which considers conduction and convection both, and allows continuous boiling over an extended region unlike the previous low-leakage rate model which neglects convection and always forces a discrete boiling interface. Another simplified, semi-analytical model, based on the assumption of isothermal conditions along the seal interafce, has been developed for low leakage rates. The Film Coefficient Model may be used for more accurate and realistic description.

Basu, Prithwish↗