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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Vertical axis wind rotors: Status and potential

The design and application of a vertical axis wind rotor is reported that operates as a two stage turbine wherein the wind impinging on the concave side is circulated through the center of the rotor to the back of the convex side, thus decreasing what might otherwise be a high negative pressure region. Successful applications of this wind rotor to water pumps, ship propulsion, and building ventilators are reported. Also shown is the feasibility of using the energy in ocean waves to drive the rotor. An analysis of the impact of rotor aspect ratio on rotor acceleration shows that the amount of venting between rotor vanes has a very significant effect on rotor speed for a given wind speed.

Vance, W.↗
NASA NTRS1974

Propagation of waves along an impedance boundary

A theoretical analysis of the scalar wave field due to a point source above a plane impedance boundary is presented. A surface wave is found to be an essential component of the total wave field. It is shown that, as a result of ducting of energy by the surface wave, the amplitude of the total wave near the boundary can be greater than it would be if the boundary were perfectly reflecting. Asymptotic results, valid near the boundary, are obtained both for the case of finite impedance (the soft-boundary case) and for the limiting case in which the impedance becomes infinite (the hard-boundary case). In the latter, the wave amplitude in the farfield decreases essentially inversely as the horizontal propagation distance; in the former (if the surface-wave term is neglected), it decreases inversely as the square of the horizontal propagation distance.

Wenzel, A. R.↗
NASA NTRS1974

Generalized Heisenberg theory of turbulence

Solutions of the generalized theory are obtained which are consistent with the previous work on energy transfer measurements. They also agree with the measurements of turbulent energy spectrum for wave numbers in the universal equilibrium range.

Uberoi, M. S.↗
NASA NTRS1975

The triggering and subsequent development of a solar flare

High temporal and spatial resolution solar X-ray pictures of a flare at 1827 UT on 5 September 1973 were taken with the S-056 telescope on the Apollo telescope mount. Photographs taken at 9 sec intervals allow detailed information to be obtained about the site of the energy release, as well as about the evolution of the flare itself. Observations suggest that the flare occurred in an entire arcade of loops rather than in any single loop. Sequential brightening of different X-ray features indicates that some excitation moved perpendicular to the magnetic field of the arcade at velocities of 180 to 280 km/sec. The most intense X-ray features were located in places where the magnetic field composing the arcade had a small radius of curvature with horizontal field gradients higher than the surroundings region and where the axis of the arcade changed direction. It was felt that the arcade geometry strongly influenced the propagation of the triggering disturbance, as well as the storage and site of the subsequent deposition of energy. A magnetosonic wave is suggested as the propagating mechanism triggering instabilities that may have existed in the preflare structure.

Vorpahl, J. A.↗
NASA NTRS1976

The triggering and subsequent development of a solar flare

A solar flare which occurred on Sept. 5, 1973, is discussed on the basis of high temporal and spatial resolution pictures taken with the Skylab S-056 X-ray telescope. The temporal evolution of the flare is outlined, and magnetic-field data for the active region are compared with the soft X-ray observations. A close similarity between calculated magnetic-field lines and the overall structure of the X-ray core is shown to suggest that the flare occurred in an entire arcade of loops rather than in a single loop. Sequential brightening of different X-ray features is taken as an indication that some triggering disturbance moved from one side to the other in the flare core at velocities of 180 to 280 km/s. The two most intense X-ray features were found in places where the magnetic field composing the arcade had a small radius of curvature with horizontal field gradients higher than the surrounding area and where the axis of the arcade changed direction. It is suggested that a magetosonic wave triggered the energy releases as it propagated down the arcade and steepened the field gradients

Vorpahl, J. A.↗
NASA NTRS1980

Quantitative ultrasonic evaluation of engineering properties in metals, composites, and ceramics

Ultrasonic techniques that have demonstrated potential for material characterization are reviewed. These techniques rely on physical acoustic properties of materials and the interaction of elastic stress waves with morphological factors in the ultrasonic regime. The speed of wave propagation and energy loss by interaction with material microstructure and geometrical factors underlie ultrasonic determination of material properties. Two categories of ultrasonic measurements are discussed: those related to material strengths (e.g., elastic moduli, tensile strength, and fracture toughness) and those related to morphology and material conditions that govern strength and performance (e.g., microstructure, void content, residual stress, fatigue damage). It is shown that large-scale industrial application of ultrasonic NDE will depend on advancement in such areas as theory development, instrumentation, system automation, standardization, and coordination with design.

Vary, A.↗
NASA NTRS1981

Electrical coupling between the lower atmosphere and the ionosphere

The evidence for interactions between the ionosphere and troposphere is reviewed as a first step in establishing the role of electrical coupling between two regions. Upward processes appear to include the transfer of energy through gravity waves, or through the transmittance of VLF radio waves induced by lightning. In each case, the excitation of the upper atmosphere by tropospheric sources can stimulate feedback processes returning to the troposphere. Downward coupling involves changes in the global and local electrical structure of the atmosphere, and is often induced by solar activity. These effects are more direct and may possibly bypass the stratosphere. The responses in the atmospheric circuit to local changes are nearly instantaneous, and therefore are looked on with promise for possible influences on weather systems. Emerging experimental evidence indicates that atmospheric electric fields, especially at high latitudes and in the upper atmosphere, are responsive to solar and geomagnetic phenomena. Corpuscular radiations are known to strongly enhance the local atmospheric electrical conductivity and ionizations at stratospheric and mesospheric altitudes. Theories postulate that the electric field perturbations regulated by solar activity may be responsibile for the observed statistical correlations between solar activity and thunderstorms.

Goldberg, R. A.↗
NASA NTRS1984

In Situ Data

In-situ planetary data include all measurements made by a wide variety of instruments whose sensors are exposed directly to the planetry environment. Typical measurements include those of magnetic fields, energetic particle densities and energy distributions, plasma wave characteristics, ionospheric and neutral gas densities, temperatures, composition and motions. A large body of scientists in the United States, and the world, are involved in research using in-situ data. Many of these scientists are associated with Mission investigations groups which provide specific types of in-situ data. These groups, in the course of data analysis, use data provided by similar groups. The interdisciplinary nature of these investigations fosters exchange and reliance upon one another for data is heavy. To a lesser extent, correlative data sets are obtained from the National Space Science Data Center (NSSDC). However, the data entries often have limited temporal and spatial resolution, are of uncertain quality, and are usually available only for measurements that are several years old.

Source record↗
NASA NTRS1984

Analysis of active control by surface heating

The excitation of boundary-layer disturbances by active, localized periodic heating of the flow surfaces is investigated analytically. A triple-deck model is used in the matched-asymptotics approach, and the incompressible case with small temperature variations, a linearized 3-deck problem, is considered. This case corresponds to the experimental (water-tunnel) conditions of Liepmann et al. (1982), who demonstrated that the induced disturbances can be used to enhance or suppress the Tollmien-Schlichting waves. Here the energy equation is uncoupled from the momentum and continuity equations to permit definition of the thermal-sublayer temperature profile by superposition of canonical solutions, which are presented in an appendix. A diagram of the 3-deck structure and graphs of calculated results are included.

Maestrello, L.↗
NASA NTRS1984

Apparent solar temperature enhancement due to large-amplitude waves

The effect of slow-mode acoustic-type MHD waves propagating outward in the solar atmosphere on the temperature structures predicted by empirical models is investigated analytically. A model is constructed, and numerical results are presented for wing intensities, line profiles, temperature enhancements, waves with higher energy flux, temperature depression, and the Si continuum. The flux in the MgII and CaII UV resonance lines is found to be increased relative to that in the IR continuum, leading to model temperatures which depend systematically on which observations are used in the computation. It is suggested that mechanical heating may take place in smaller regions such as flux tubes rather than uniformly over the surface.

Kalkofen, W.↗
NASA NTRS1986

Working group report on beam plasmas, electronic propulsion, and active experiments using beams

The JPL Workshop addressed a number of plasma issues that bear on advanced spaceborne technology for the years 2000 and beyond. Primary interest was on the permanently manned space station with a focus on identifying environmentally related issues requiring early clarification by spaceborne plasma experimentation. The Beams Working Group focused on environmentally related threats that platform operations could have on the conduct and integrity of spaceborne beam experiments and vice versa. Considerations were to include particle beams and plumes. For purposes of definition it was agreed that the term particle beams described a directed flow of charged or neutral particles allowing single-particle trajectories to represent the characteristics of the beam and its propagation. On the other hand, the word plume was adopted to describe a multidimensional flow (or expansion) of a plasma or neutral gas cloud. Within the framework of these definitions, experiment categories included: (1) Neutral- and charged-particle beam propagation, with considerations extending to high powers and currents. (2) Evolution and dynamics of naturally occurring and man-made plasma and neutral gas clouds. In both categories, scientific interest focused on interactions with the ambient geoplasma and the evolution of particle densities, energy distribution functions, waves, and fields.

Dawson, J. M.↗
NASA NTRS1986

Thermal stability analysis of the fine structure of solar prominences

The linear thermal stability of a 2D periodic structure (alternatively hot and cold) in a uniform magnetic field is analyzed. The energy equation includes wave heating (assumed proportional to density), radiative cooling and both conduction parallel and orthogonal to magnetic lines. The equilibrium is perturbed at constant gas pressure. With parallel conduction only, it is found to be unstable when the length scale 1// is greater than 45 Mn. In that case, orthogonal conduction becomes important and stabilizes the structure when the length scale is smaller than 5 km. On the other hand, when the length scale is greater than 5 km, the thermal equilibrium is unstable, and the corresponding time scale is about 10,000 s: this result may be compared to observations showing that the lifetime of the fine structure of solar prominences is about one hour; consequently, our computations suggest that the size of the unresolved threads could be of the order of 10 km only.

Demoulin, Pascal↗