Civil Engineering Reference
In-Depth Information
Adrian's group intensively analyzed the evolution of wall
turbulence under the influence of the injection of a structure
extracted by linear stochastic estimation by means of the
two-point correlations of the velocity field conditioned by an
event in quadrant
II
. Figure 3.17 shows the type of
structures thus injected. An overview of the results obtained
by this approach is presented in [ADR 07]. Thus, the
regenerated structures are artificial, and we inevitably see
the formation of clusters of HPVs, under certain conditions,
which will be analyzed in detail in Chapter 6. Figure 4.6
illustrates such a chaotic cluster of HPVs. It is not
inconceivable to occasionally observe clusters of HPVs in the
real world of wall turbulence, simulated numerically in
turbulent channel flows subject to periodic boundary
conditions [ADR 02].
Although
according to
our own
experience acquired with DNS in large domains of
computation, hairpin vortex structures are relatively rare
statistically, accounting for 10-20% of the total population,
and are less present than QSVs, if only up to
Re
τ
=
1,100.
Figure 4.6.
Cluster of hairpin vortices resulting from direct numerical
simulations in a channel flow at
Re = 395 . The initial condition at
t
+
0
is a symmetrical structure, similar to that shown in Figure 3.17 obtained
by linear stochastic estimation. The cluster of aligned HPVs shown in this
figure corresponds to
t = 356
. This figure is adapted from [ADR 07]. For a
color version of this figure, see www.iste.co.uk/tardu/wallturbulence.zip
=
τ
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