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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
DOE OSTI2020

Does the rotational direction of a wind turbine impact the wake in a stably stratified atmospheric boundary layer?

Stably stratified atmospheric boundary layers are often characterized by a veering wind profile, in which the wind direction changes clockwise with height in the Northern Hemisphere. Wind-turbine wakes respond to this veer in the incoming wind by stretching from a circular shape into an ellipsoid. We investigate the relationship between this stretching and the direction of the turbine rotation by means of large-eddy simulations. Clockwise rotating, counterclockwise rotating, and non-rotating actuator disc turbines are embedded in wind fields of a precursor simulation with no wind veer and in wind fields with a Northern Hemispheric Ekman spiral, resulting in six combinations of rotor rotation and inflow wind condition. The wake strength, extension, width, and deflection depend on the interaction of the meridional component of Ekman spiral with the rotational direction of the actuator disc, whereas the direction of the disc rotation only marginally modifies the wake if no veer is present. The differences result from the amplification or weakening/reversion of the spanwise and the vertical wind components due to the effect of the superposed disc rotation. They are also present in the streamwise wind component of the wake and in the total turbulence intensity. In the case of an counterclockwise rotating actuator disc, the spanwise and vertical wind components increase directly behind the rotor, resulting in the same rotational direction in the whole wake while its strength decreases downwind. In the case of a clockwise rotating actuator disc, however, the spanwise and vertical wind components of the near wake are weakened or even reversed in comparison to the inflow. This weakening/reversion results in a downwind increase in the strength of the flow rotation in the wake or even a different rotational direction in the near wake in comparison to the far wake. The physical mechanism responsible for this difference can be explained by a simple linear superposition of a veering inflow with a Rankine vortex.

17 WIND ENERGY↗
DOE OSTI2020

Exploring nuclear exotica at the limits

The study of nuclear limits has been performed and new physical mechanisms and exotic shapes allowing the extension of nuclear landscape beyond the commonly accepted boundaries have been established. The transition from ellipsoidal to toroidal shapes plays an essential role in potential extension of nuclear landscape to hyperheavy nuclei. Moreover, rotational excitations leading to the birth of particle (proton or neutron) bound rotational bands provide a mechanism for an extension of nuclear landscape beyond spin zero proton and neutron drip lines.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1966

High-speed furnace uses infrared radiation for controlled brazing

Furnace produces controlled heat for brazing and heat treating metals over a wide range of temperatures by using a near-infrared heat source positioned at one focus of an ellipsoidal reflector mounted below a cylindrical quartz chamber. This furnace maintains a pure atmosphere, has rapid heatup and cooldown, and permits visual observation.

Eckles, P. N.↗
NASA NTRS1968

Antiglare improvement for optical imaging systems

Baffle configuration provides a more efficient shade against interfering sources of illumination outside the desired field of view of optical imaging systems. It consists of a semi-ellipsoid of revolution about the minor axis with black specular reflecting surface and an aperture defined by the locus of the foci of the generating ellipse.

Davis, E. S.↗
NASA NTRS1969

Determination of quadric equation coefficients describing three-dimensional surfaces, their constraint and skewed planes, and view point areas

Mathematical model and a digital computer BLITZ language programming technique computes coefficients of quadric equations describing cylinders, paraboloids, ellipsoids, or planes with any orientation to a reference system, coordinates of a vector, and coefficients of quadric surfaces which limit the surface of three-dimensional space.

Paoletti, C. J.↗
NASA NTRS1968

On the Equilibrium Figure of the Earth

If de Sitter's hydrostatic equations are developed independent of the external potential theory, the hydrostatic geopotential coefficient J(sub h) occurs explicitly on the right-hand side of those equations. J(sub h) here has to be treated as an unknown in the solution, it becomes rather difficult to solve the equations independently, regardless of which of the dynamical parameters associated with the earth is taken as the initial datum. Solution is possible, however, with the help of a boundary condition derived from the external potential theory which neither assumes nor discounts the presence of equilibrium conditions in the earth's interior. If a general solution i s constructed on this basis, the three particular solutions, usually quoted in literature, stem from it in the wake of the appropriate assumptions. Of course, the only meaningful solution--of these-- is that corresponding to the polar moment of inertia as the initial datum. It is essential that the solution be constructed in this way in order to demonstrate clearly the correct structure of the problem of hydrostatic equilibrium. The anomalous gravity field of the earth referred to the hydrostatic figure is compared with that referred to the international reference ellipsoid.

Khan, M. A.↗
NASA NTRS1970

High intensity heat-pulse source operates without cooling system

Tungsten-iodine quartz lamp with on-off control is mounted at focus of ellipsoidal reflector and shutter is mounted at conjugate focus. Flux sensor monitors lamp and actuates shutter which emits a heat pulse when the radiant flux builds up to requisite level.

Russell, L. D.↗
NASA NTRS1971

Orbital accelerations of the Pageos spacecraft

Pageos spacecraft orbital acceleration prediction by radiation pressure perturbation theory accounting for nonisotropic scattering of solar spectra from rotating ellipsoidal body

Kissell, K. E.↗
NASA NTRS1971

An experimental study of axisymmetric modes in various propellant tanks containing liquid

An experimental study of several models used to analyze the longitudinal dynamics of oscillations in launch vehicle propellant tanks, is presented. Several vehicle structural configurations are considered: hemispherical and spherical, cylindrical and spherical, and semiellipsoidal and ellipsoidal. Various bulkheads and flanges are used with each configuration. The results are given in graphs.

Kana, D. D.↗
NASA NTRS1971

Further studies of propellant sloshing under low-gravity conditions

A variational integral is formulated from Hamilton's Principle and is proved to be equivalent to the usual differential equations of low-gravity sloshing in ellipsoidal tanks. It is shown that for a zero-degree contact angle the contact line boundary condition corresponds to the stuck condition, a result that is due to the linearization of the equations and the ambiguity in the definition of the wave height at the wall. The variational integral is solved by a Rayleigh-Ritz technique. Results for slosh frequency when the free surface is not bent-over compare well with previous numerical solutions. When the free surface is bent over, however, the results for slosh frequency are considerably larger than those predicted by previous finite-difference, numerical approaches: the difference may be caused by the use of a zero degree contact angle in the present theory in contrast to the nonzero contact angle used in the numerical approaches.

Dodge, F. T.↗