Regeneration and Self-Maintaining of Coherent Structures - Transport and Coherent Structures in Wall Turbulence - page 365

A and B are indicated, respectively, by and in

ω ± ω ±

yA yB

Figure 5.44.

Figure 5.44. View of a section of two CRVPs in the plane y-z. The pair A
regenerates the wall-normal vorticity layers which are positive and

negative, respectively, on the left and on the right. Two similar vorticity
layers

ω ±

yA

are regenerated by the pair B. The pair B is shifted in relation
to the center of symmetry of A

ω ±

yB

requires the regeneration of the
streamwise variations of the zones

The creation of

∂∂ wx

. There will
be no regeneration if the spanwise symmetry, in direction z ,
is not broken. Thus, the “break-up” of the streaks in a
turbulent boundary layer is systematically preceded by
streamwise variations of the walls

and/or ω ω

x

y

associated therewith.

ω

y

The mechanism in question is detailed in [TAR 95a]. It is
based on observations obtained mainly by Brooke and
Hanratty [BRO 93] and Jiménez [JIM 94]. The aim here is to
demonstrate and illustrate this process, by the example of a
specific interaction of two localized disturbances. Indeed, in
Figure 5.44, we can see that the vortex pair B is shifted in
the spanwise direction. The structure B acts as a catalyst