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J. Fluid Mech. (2008), vol. 607, pp. 119139. c 2008 Cambridge University Press doi:10.1017/S0022112008001882 Printed in the United Kingdom
 

Summary: J. Fluid Mech. (2008), vol. 607, pp. 119­139. c 2008 Cambridge University Press
doi:10.1017/S0022112008001882 Printed in the United Kingdom
119
Torsional oscillations of the large-scale
circulation in turbulent Rayleigh­B´enard
convection
DENIS FUNFSCHILLING, ERIC BROWN
AND GUENTER AHLERS
Department of Physics and iQCD, University of California, Santa Barbara, CA 93106, USA
(Received 8 May 2007 and in revised form 28 March 2008)
Measurements over the Rayleigh-number range 108 < R < 1011
and Prandtl-number
range 4.4 < < 29 that determine the torsional nature and amplitude of the oscillatory
mode of the large-scale circulation (LSC) of turbulent Rayleigh­B´enard convection
are presented. For cylindrical samples of aspect ratio = 1 the mode consists of
an azimuthal twist of the near-vertical LSC circulation plane, with the top and
bottom halves of the plane oscillating out of phase by half a cycle. The data for
= 1 and = 4.4 showed that the oscillation amplitude varied irregularly in time,
yielding a Gaussian probability distribution centred at zero for the displacement
angle. This result can be described well by the equation of motion of a stochastically

  

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

 

Collections: Physics