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Astron. Astrophys. 317, 290-298 (1997)

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Rotational effects in turbulence driven by convection

Cesar Meirelles Filho 1, 2, 3, Mauricio R.Ruiz 1 and Chuan Luo 1

1 Space Physics and Astronomy Department, Rice University, Houston, TX 77005, USA
2 Physics of High Energy Plasmas, Massachusetts Institute of Technology, Cambridge, MA 02139
3 Present Address: Instituto de Fisica, Universidade de Sao Paulo, C.P. 66318, 05389-970 Sao Paulo, SP, Brazil (meirelles@if.usp.br)

Received 18 April 1994 / Accepted 4 April 1996

Abstract

We analyze rotational effects in turbulence driven by convection in the outer regions of an accretion disk, where opacity is mainly given by ice. These effects are explicitly considered through the introduction of an efficiency factor which takes into account inverse energy cascade processes and through the consideration of a centrifugally supported basic state. By adopting a procedure which assigns some dynamics to the anisotropy factor, we obtain an equation that describes how the turbulent structures behave along the disk. Stationary solutions to that equation are only found if the accretion rate, the efficiency factor, the rotational intensity and the Brunt-Väisälä frequency satisfy a known critical condition. If the rotational intensity is below the critical one, there are two branches of solutions for that equation. If the accretion rate is not very high, the effective Rayleigh number for the onset of the convective instability decreases and, in the upper branch, longitudinal scales are always greater than the horizontal scales; in the lower branch, as we approach the surface of the disk, horizontal scales become greater than longitudinal ones. In both branches, centrifugal effects prevail over the effects due to the Coriolis force. If the accretion rate is high, the effective Rayleigh number for the onset of the convective instability increases. In the lower branch, the size of the turbulent structures increases as [FORMULA] ; in the upper branch, the size of the turbulent structures decreases as [FORMULA]. In the lower branch, generation of waves occurs all long the disk. In the upper branch, it is confined to regions close to the point where convection sets in. For those high values of the accretion rate, the effects due to the Coriolis force prevail over the those due to the centrifugal forces.

Key words: accretion — turbulence — convection

Send offprint requests to: C. Meirelles Filho (at present address)

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