Large- and Very Large-scale Structures - Transport and Coherent Structures in Wall Turbulence - page 381

Packets are not large-scale structures with a negligible
dynamical role; they are, in fact, far from it. The contribution
made by packets to the quadrant- II events, which is defined
by

∑
∑

−
= −

uv

∈ PS

c

PS

uv

∈ QII

is greater than the contribution of solitary ejections at c

SS

y +

, as shown in Figure 6.6. The sum is

> 50

cc +

PS SS

obviously the contribution of the ejections to quadrant

II
and is 70% according to the results advanced by Luchik and
Tiederman [LUC 87].

,

Figure 6.6. Contribution of packets of structures to
quadrant-II events at Re = 500

t

6.4. Kinematic consequences of coherent clustering of
structures

Packets of structures give rise to local wakes. The
coherent alignment of these wakes in the streamwise