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  • Weitere Quellen  (6)
  • 1975-1979  (6)
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  • 1
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    In:  Other Sources
    Publikationsdatum: 2019-06-27
    Beschreibung: We expand the fluctuating flow variables of Boussinesq convection in the planform functions of linear theory. Our proposal is to consider a drastic truncation of this expansion as a possible useful approximation scheme for studying cellular convection. With just one term included, we obtain a fairly simple set of equations which reproduces some of the qualitative properties of cellular convection and whose steady-state form has already been derived by Roberts (1966). This set of 'modal equations' is analyzed at slightly supercritical and at very high Rayleigh numbers. In the latter regime the Nusselt number varies with Rayleigh number just as in the mean-field approximation with one horizontal scale when the boundaries are rigid. However, the Nusselt number now depends also on the Prandtl number in a way that seems compatible with experiment. The chief difficulty with the approach is the absence of a deductive scheme for deciding which planforms should be retained in the truncated expansion.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: Journal of Fluid Mechanics; 68; Apr. 29
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2019-06-28
    Beschreibung: A linear stability analysis of fluid layers under uniform rotation (generally oblique to gravity) which possess both vertical and horizontal temperature gradients is made by considering ideal fluids without diffusion within a Boussinesq approximation. This simplified configuration is used to assess the preferred convective modes as a function of latitude on a planet like Jupiter. The tilted rotation vector introduces a preference for roll-like disturbances with north-south orientations, while the horizontal temperature gradient produces a thermal wind shear which favors convective rolls oriented parallel to the flow in an east-west direction. It is found that the horizontal temperature gradient needed to produce a preference for the axisymmetric or east-west rolls increases with an increasing rotation rate and a decreasing latitude. The parameter values for Jupiter are estimated with the use of a simple radiative convective model, indicating a preference for axisymmetric rolls at nearly all latitudes if the convection zone depth is greater than about 200 km below the one atmosphere pressure level and convective roll characteristics which contribute to an equatorial acceleration.
    Schlagwort(e): GEOSCIENCES (GENERAL)
    Materialart: AD-A085390 , AFGL-TR-80-0103 , Geophysical and Astrophysical Fluid Dynamics; 13; 4, 19; 1979
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2019-06-27
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; 207; July 15
    Format: text
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  • 4
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    Unbekannt
    In:  Other Sources
    Publikationsdatum: 2019-06-27
    Beschreibung: In the Boussinesq approximation, single-mode equations describing thermal convection are constructed by expanding the fluctuating velocity and temperature fields in a complete set of functions (or planforms) of the horizontal coordinates and retaining just one term. Numerical solutions of the single-mode equations are investigated, chief consideration being given to hexagonal planforms. Extensive surveys of steady solutions are presented for various Rayleigh numbers, Prandtl numbers, and horizontal wavenumbers. The dependences on Rayleigh number and Prandtl number at very large Rayleigh number are in satisfactory agreement with the results of asymptotic expansions.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: Journal of Fluid Mechanics; 79; Jan. 20
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2019-06-27
    Beschreibung: Methods are developed for dealing with the various dynamical problems that arise because of convective zones in stars. A system of equations for stellar convection is derived from the full equations of compressible fluid dynamics with the aid of two major approximations. The first of these is the anelastic approximation, which involves both the filtering out of acoustic waves and a suitable linearization of the fluctuating thermodynamic variables. The second one approximates the horizontal structure of convection by expanding the motion in a set of horizontal cellular platforms and severely truncating the expansion. The resulting system of partial differential equations, referred to as the anelastic modal equations, is outlined along with suggested boundary conditions and techniques for solving the equations. Ways of assessing the overall validity of the present treatment are discussed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal; 207; July 1
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2019-06-27
    Beschreibung: Results are reported for simultaneous satellite and ground-based observations of supergranular velocities in the sun, which were made using a UV spectrometer aboard OSO 8 and a diode-array instrument operating at the exit slit of an echelle spectrograph attached to a vacuum tower telescope. Observations of the steady Doppler velocities seen toward the limb in the middle chromosphere and the photosphere are compared; the observed spectral lines of Si II at 1817 A and Fe I at 5576 A are found to differ in height of formation by about 1400 km. The results show that supergranular motions are able to penetrate at least 11 density scale heights into the middle chromosphere, that the patterns of motion correlate well with the cellular structure seen in the photosphere, and that the motion increases from about 800 m/s in the photosphere to at least 3000 m/s in the middle chromosphere. These observations imply that supergranular velocities should be evident in the transition region and that strong horizontal shear layers in supergranulation should produce turbulence and internal gravity waves.
    Schlagwort(e): SOLAR PHYSICS
    Materialart: PB-294163 , Astrophysical Journal; vol. 227
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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