Large- and Very Large-scale Structures - Transport and Coherent Structures in Wall Turbulence - page 414

and w also increase
with increasing distance from the wall. However, they are
markedly decoupled from the streamwise velocity scales.
Remember that production is written as

The characteristic scales of v , uv

−

( )

+

Puv Uy

+

=− ∂∂

+ +

= 1 κ y

+

in the logarithmic sublayer for Re . It rapidly becomes

insignificant in comparison to P + in the inner layer. The
large- and very large-scale structures undoubtedly transport
a significant proportion of the Reynolds shear stress in the
logarithmic sublayer. However, it seems difficult to envisage
their playing a significant dynamic role in a zone where the
mean production is small, unless they directly affect P + in
the buffer sublayer.

τ →∞

The inner sublayer

y +

is essentially governed by the

< 100

wall parameters . The numerical experiments

conducted by Jimenez et al . [JIM 04], in which the
fluctuations in vorticity from the outer sublayer were
artificially removed, showed that the structure of the inner
sublayer is robust and has only a marginal dependence on
the large-scale structures originating in the outer flow. As
previously indicated in this topic, the predominant length
scales of the characteristic individual units in the inner
sublayer are

and u ν

τ

in the streamwise direction, which is
simply the length of the quasi-streamwise vortices and
100

L +

= 400

in the spanwise direction - a scale that corresponds
to the spacing of the high- and low-velocity streaks. The
formation of the packets and the coherent alignment of their
wakes give rise to structures whose length scale may exceed
1, 0 0 0

L +

=

, as discussed at the beginning of this chapter.
These structures carry and transport energy uu . Given that
the packets are made up of individual vortices, structures

L +

≥