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Effect of the Earth's Coriolis force on the large-scale circulation of turbulent Rayleigh-Bnard convection

Summary: Effect of the Earth's Coriolis force on the large-scale circulation
of turbulent Rayleigh-Bénard convection
Eric Brown and Guenter Ahlers
Department of Physics and iQCD, University of California, Santa Barbara, California 93106
Received 21 July 2006; accepted 8 November 2006; published online 19 December 2006
We present measurements of the large-scale circulation LSC of turbulent Rayleigh-Bénard
convection in water-filled cylindrical samples of heights equal to their diameters. The orientation of
the LSC had an irregular time dependence, but revealed a net azimuthal rotation with an average
period of about 3 days for Rayleigh numbers R 1010
. On average there was also a tendency for the
LSC to be aligned with upflow to the west and downflow to the east, even after physically rotating
the apparatus in the laboratory through various angles. Both of these phenomena could be explained
as a result of the coupling of the Earth's Coriolis force to the LSC. The rate of azimuthal rotation
could be calculated from a model of diffusive LSC orientation meandering with a potential barrier
due to the Coriolis force. The model and the data revealed an additional contribution to the potential
barrier that could be attributed to the cooling system of the sample top that dominated the preferred
orientation of the LSC at high R. The tendency for the LSC to be in a preferred orientation due to
the Coriolis force could be canceled by a slight tilt of the apparatus relative to gravity, although this
tilt affected other aspects of the LSC that the Coriolis force did not. © 2006 American Institute of
Physics. DOI: 10.1063/1.2402875


Source: Ahlers, Guenter - Department of Physics, University of California at Santa Barbara


Collections: Physics