Large- and Very Large-scale Structures - Transport and Coherent Structures in Wall Turbulence - page 412

high as , with a slight dependence on the Reynolds

number (Figure 6.25). Note that this zone is clearly in the
outer sublayer because the upper bound of the logarithmic
sublayer is

L

/ Λ= 4

0

, according to Marusic et al. [MAR 13].
It should also be pointed out that the order of magnitude
[6.9] proves to be more or less adequate. The significant
scales contributing to half of the cumulative streamwise
energy are twice as large as those transporting the Reynolds
shear stress, as illustrated in Figure 6.25.

y Λ= 0.15

0

Figure 6.26 shows the contours / uu , / vv and

( )

2

in the logarithmic layer at and

uv / uv uv −

y Λ= 0.27

0

, in a limited portion of the domain of calculation
that extends up to

Re

τ =

1, 1 0 0

in
direction z . These results need to be compared to those
shown in Figure 6.27 and Figure 6.28, which show the same
contours in the buffer sublayer at

+

in direction x and up to

+

8 π Λ 3 π Λ

0 0

. It is clear that the
streamwise and spanwise length scales of the streaks
induced by the wake and the amalgamation of the packets of
structures increase as we move further from the wall
(Figure 6.26(a) and Figure 6.27(a). According to Del Alamo et
al. [ALA 04], the characteristic length scales vary as

y + = 15

2
z

LL ∝

x

in the logarithmic sublayer. However, the spanwise length
has an approximately linear dependency on the distance
from the wall in that sublayer [TOM 03]. These

considerations imply a linear increase in L with increasing
y in the logarithmic sublayer. This increase peters out
further away from the wall, in the wake sublayer.

z Ly

∝