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subsequently by du Puits et al. (
2007
). The absence of wind could be either a con-
sequence of a completely random motion, or due to the formation of more complex
structures. Resolving this kind of questions experimentally requires the visualization
of the global flow structure. To our knowledge, the highest Rayleigh number in a
large aspect ratio experiment is
10
9
9 in the air experiments by du Puits
et al. (
2013
). If we consider only the experiments that visualized the global flow
structures, the maximum Rayleigh number is
Ra
∼
for
ʓ
=
10
7
11 cell by
Hogg and Ahlers (
2013
). More experiments at large aspect ratios and large
Ra
are
therefore needed, in particular with capabilities for visualizing the flow structures
(see Fig.
6
).
=
2
×
in the
ʓ
=
10
18
10
16
10
14
10
12
Ra
10
10
10
8
10
6
10
4
0
2
4
8
10
12
ʓ
Wu and Libchaber 1992 (He)
Whitehead and Parsons 1977 (Silicone Oil)
Niemela et al. 2000 (He)
Niemela and Sreenivasan 2003 (He)
Niemela and Sreenivasan 2006 (He)
Urban et al. 2014 (He)
Krishnamurti and Howard 1981 (Water)
Hogg and Ahlers 2013 (gases)
Xia et al. 2003 (water)
Verdoold et al. 2006 (water)
Ahlers et al. 2012 (SF6)
Shishkina and Wagner 2005 (DNS)
von Hardenberg et al. 2008 (DNS)
He et al. 2012a (SF6)
Funfschilling et al. 2005 (water)
du Puits et al. 2013 (air)
Bailon-Cuba et al. 2010 (DNS)
Fig. 6
The plot shows the maximum Rayleigh numbers achieved by some selected experiments
and simulations for different values of the aspect ratio. Open symbols denote conditions for possible
visualization
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