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Heat transport by turbulent rotating Rayleigh–Bénard convection and its dependence on the aspect ratio
Published online by Cambridge University Press: 02 September 2011
Abstract
We report on the influence of rotation about a vertical axis on heat transport by turbulent Rayleigh–Bénard convection in a cylindrical vessel with an aspect ratio (
is the diameter and
the height of the sample) and compare the results with those for larger
. The working fluid was water at
where the Prandtl number
is 4.38. For rotation rates
, corresponding to inverse Rossby numbers
between zero and twenty, we measured the Nusselt number
for six Rayleigh numbers
in the range
. For small rotation rates and at constant
, the reduced Nusselt number
initially increased slightly with increasing
, but at
it suddenly became constant or decreased slightly depending on
. At
a second sharp transition occurred in
to a state where
increased with increasing
. We know from direct numerical simulation that the transition at
corresponds to the onset of Ekman vortex formation reported before for
at
and for
at
(Weiss et al., Phys. Rev. Lett., vol. 105, 2010, 224501). The
-dependence of
can be explained as a finite-size effect that can be described phenomenologically by a Ginzburg–Landau model; this model is discussed in detail in the present paper. We do not know the origin of the transition at
. Above
,
increased with increasing
up to
. We discuss the
-dependence of
in this range in terms of the average Ekman vortex density as predicted by the model. At even larger
there is a decrease of
that can be attributed to two possible effects. First, the Ekman pumping might become less efficient when the Ekman layer is significantly smaller than the thermal boundary layer, and second, for rather large
, the Taylor–Proudman effect in combination with boundary conditions suppresses fluid flow in the vertical direction.
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