  The widest spanwise scales in turbulent channel flows are studied through the
use of three periodic channel-flow simulations at friction Reynolds number
$\mathrm{Re}_{\tau}=550$. The length and height of the channels are the same in
all cases ($L_x/h=8\pi$ and $L_y/h=2$ respectively), while the width is
progressively doubled: $L_z/h = \{4\pi, 8\pi, 16\pi\}$. The effects of
increasing the domain can not be determined with statistical significance in
our simulations, since the difference in the statistics between the simulations
is of the same order as the errors of convergence. A channel flow similar to
the smaller one ($\textit{J. Fluid Mech.}$, vol. 500, 2004, pp. 135--144),
which was averaged over a very long time, was used as a reference. The
one-dimensional spanwise spectrum of the streamwise velocity is computed with
the aim of assessing the domain-size effect on the widest scales. Our results
indicate that $90\%$ of the total streamwise energetic fluctuations is
recovered without a significant influence of the size of the domain. The
remaining $10\%$ of the energy reflects that the widest scales in the outer
layer are the ones most significantly affected by the spanwise length of the
domain. The power-spectral density for $k_z = 0$ remains constant even if the
size of the domain in the spanwise direction is increased up to 4 times the
standard spanwise length, indicating that wide, spanwise coherent structures
are not an artifact of domain truncation.
