Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Universal fluctuations in the bulk of Rayleigh-B\'enard turbulence   We present an investigation of the root-mean-square (rms) temperature
$\sigma_T$ and the rms velocity $\sigma_w$ in the bulk of Rayleigh-B\'enard
turbulence, using new experimental data from the current study and experimental
and numerical data from previous studies. We find that, once scaled by the
convective temperature $\theta_*$, the value of $\sigma_T$ at the cell centre
is a constant, i.e. $\sigma_{T,c}/\theta_* \approx 0.85$, over a wide range of
the Rayleigh number ($10^{8}\leq Ra\leq 10^{15}$) and the Prandtl number
($0.7\leq Pr \leq 23.34$), and is independent of the surface topographies of
the top and bottom plates of the convection cell. A constant close to unity
suggests that $\theta_*$ is a proper measure of the temperature fluctuation in
the core region. On the other hand, $\sigma_{w,c}/w_*$, the vertical rms
velocity at the cell centre scaled by the convective velocity $w_*$, shows a
weak $Ra$-dependence ($\sim Ra^{0.07\pm0.02}$) over $10^8\leq Ra\leq 10^{10}$
at $Pr\sim4.3$ and is independent of plate topography. Similar to a previous
finding by He \& Xia ({\it Phys. Rev. Lett.,} vol. 122, 2019, 014503), we find
that the rms temperature profile $\sigma_T(z)/\theta_*$ in the region of the
mixing zone with a mean horizontal shear exhibits a power-law dependence on the
distance $z$ from the plate, but now the universal profile applies to both
smooth and rough surface topographies and over a wider range of $Ra$. The
vertical rms velocity profile $\sigma_w(z)/w_*$ obey a logarithmic dependence
on $z$. The study thus demonstrates that the typical scales for the temperature
and the velocity are the convective temperature $\theta_*$ and the the
convective velocity $w_*$, respectively. Finally, we note that $\theta_*$ may
be utilised to study the flow regime transitions in the ultra-high-$Ra$-number
turbulent convection.

0
The categories of this paper are: hep-ph
20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
2
The categories of this paper are: math
14
The categories of this paper are: math-ph
24
The categories of this paper are: dg-ga
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
17
The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas