  To isolate the multiscale dynamics of the logarithmic layer of wall-bounded
turbulent flows, a novel numerical experiment is conducted in which the mean
tangential Reynolds stress is eliminated except in a subregion corresponding to
the typical location of the logarithmic layer in channels. Various statistical
comparisons against channel flow databases show that, despite some differences,
this modified flow system reproduces the kinematics and dynamics of natural
logarithmic layers well, even in the absence of a buffer and an outer zone.
This supports the previous idea that the logarithmic layer has its own
autonomous dynamics. In particular, the results suggest that the mean velocity
gradient and the wall-parallel scale of the largest eddies are determined by
the height of the tallest momentum-transferring motions, implying that the very
large-scale motions of wall-bounded flows are not an intrinsic part of
logarithmic-layer dynamics. Using a similar set-up, an isolated layer with a
constant total stress, representing the logarithmic layer without a driving
force, is simulated and examined.
