Regeneration and Self-Maintaining of Coherent Structures - Transport and Coherent Structures in Wall Turbulence - page 372

to flows with Reynolds numbers as low as to create

synthetic local turbulence in order to improve mixing
[TAR 12].

Re = 4

The regeneration of turbulent coherent near-wall vortices
is a complex phenomenon which encompasses several
aspects. In spite of the numerous correlations that exist
between the self-sustaining mechanism of regeneration of
quasi-streamwise near-wall structures and the interactive
process proposed in this section, we cannot state that this
proposed process accounts fully for the phenomenon. The
conventional technique relating to the 3D instability of the
streaks can, though, be “bypassed” in certain conditions. The
compression/stretching of the preexisting structures on the
wall-normal vorticity layers surrounding the streaks help
speed up the transition. The process is illustrated in
Figure 5.46. The conventional mechanism as proposed in
[WAL 95, WAL 97] and [JIM 99] is shown by the solid line.
The interactive mechanism which bypasses it is represented
by the dashed line.

Figure 5.46. The generally accepted regeneration cycle
(solid line) and the interactional mechanism (dashed line).
This figure is adapted from [TAR 08a]