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(POD) and imperfect chaotic phase synchronization. The
ultimate goal of the POD approach is to reproduce the
essential dynamics of turbulence in a dynamical system of
finite dimensions. The coherent structures being advected in
the inner sublayer induce the so-called imperfect phase
synchronization of wall turbulence. This synchronization is
“hidden”, and special techniques are needed to detect it.
Chaotic synchronization of turbulence is not only important
from a fundamental point of view, but can also have
consequences for the development of strategies for
controlling wall turbulence. These aspects are briefly
discussed at the end of the chapter.
4.2. Structural morphology of wall turbulence. Quasi-
streamwise vortices or hairpin vortices?
In the previous chapter, we presented the hairpin
(or horseshoe) vortices discovered by Theodersen as being
the earliest conceptual model of coherent wall structures.
The immediate question thus is whether hairpin vortices
(HPVs) truly exist, and whether there are enough of them to
have a significant impact on the complex structures of wall
turbulence.
Figure 4.1.
Low-pressure zones on which the detection
of the vortex structures is based in [ROB 91a]
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