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J. Fluid Mech. (2006), vol. 568, pp. 351386. c 2006 Cambridge University Press doi:10.1017/S0022112006002540 Printed in the United Kingdom
 

Summary: J. Fluid Mech. (2006), vol. 568, pp. 351­386. c 2006 Cambridge University Press
doi:10.1017/S0022112006002540 Printed in the United Kingdom
351
Rotations and cessations of the large-scale
circulation in turbulent Rayleigh­B´enard
convection
By ERIC BROWN AND GUENTER AHLERS
Department of Physics and iQCD, University of California, Santa Barbara, CA 93106, USA
(Received 3 March 2006 and in revised form 18 May 2006)
We present a broad range of measurements of the angular orientation 0(t) of the
large-scale circulation (LSC) of turbulent Rayleigh-B´enard convection as a function
of time. We used two cylindrical samples of different overall sizes, but each with its
diameter nearly equal to its height. The fluid was water with a Prandtl number of
4.38. The time series 0(t) consisted of meanderings similar to a diffusive process, but
in addition contained large and irregular spontaneous reorientation events through
angles . We found that reorientations can occur by two distinct mechanisms. One
consists of a rotation of the circulation plane without any major reduction of the
circulation strength. The other involves a cessation of the circulation, followed by a
restart in a randomly chosen new direction. Rotations occurred an order of magnitude
more frequently than cessations. Rotations occurred with a monotonically decreasing

  

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

 

Collections: Physics