On the logarithmic layer in open channel flow*

We carry out DNS of open channel flow up to Re_τ=6000. Compared with the case of a full channel, the outer part of the flow exhibits organization on a larger scale, with wider scale separation between the inner and the outer energetic sites. This implies changes in the outer-layer velocity profile, which stays much closer to a genuine logarithmic distribution that in a full channel, for given Reynolds number. Velocity variances are also affected, being generally larger than in the full channel case. Our results seem to support the notion that deviations from the logarithmic behavior observed in previous channel and pipe flow DNS are likely due to limited Reynolds number, rather that to other physical effects