Coherent Wall Structures: Dynamics and Contribution to Turbulent Activity - Transport and Coherent Structures in Wall Turbulence - page 201

Robinson [ROB 91a and ROB 91b] was the first to carry
out a rigorous and methodical examination of the DNS
performed by Spallart [SPA 88]. He essentially based that
examination on the low-pressure zones to identify the
structures (see Figure 4.1). This approach is obviously
questionable, in view of our discussions from the previous
chapter. Various structures, such as quasi-streamwise
vortices (QSVs), HPVs or arc structures, were observed (as
Figure 4.2 illustrates). Yet HPVs represent only 9% of the
structures detected (see Figure 4.3). The arc structures are
most common. QSVs, for their part, account for around one-
third of the vortices detected.

Figure 4.2. Different structures identified by Robinson [ROB 91b]
and the quadrant events associated therewith

Jeong et al. [JEO 97] estimated that no vortices exist at
. They used the lambda-2 technique to detect the
structures. First, they determined the distribution of the

y + < 10

( )

1/ 2

()

2

mean value and the RMS value λλλ

'

=−

2

in λ

2

2 2 2

the inner lay er . Their results are shown in Figure 4.4. We
can see that at

y +

and that it is also comparable

λ 2 > 0 < 10