  Direct numerical simulations (DNS) of fully-developed turbulent channel flows
for very low Reynolds numbers have been performed with a larger computational
box sizes than those of existing DNS. The friction Reynolds number was
decreased down to 60, where the friction Reynolds number is based on the
friction velocity and the channel half width. When the Reynolds number was
decreased to 60 with small computational box size, the flow became laminar.
Using a large box, we found that a localized turbulence was observed to sustain
in the form of periodic oblique band. This type of locally disordered flow is
similar to a equilibrium turbulent puff in a transitional pipe flow. Various
turbulence statistics such as turbulence intensities, vorticity fluctuations
and Reynolds stresses are provided. Especially, their near-wall asymptotic
behavior and budget terms of turbulence kinetic energy were discussed with
respect to the Reynolds-number dependence and an influence of the computational
box size. Other detailed characteristics associated with the turbulence
structures were also presented and discussed.
