DNS of turbulent channel flow at very low Reynolds numbers

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.