Civil Engineering Reference
In-Depth Information
()
filtering at
E u
. It represents the
amplitude modulation imposed on the fluctuations
is written as
L
Λ>
1
0
L
S
()
S
ut
by
the large-scale structures from the logarithmic sublayer.
Figure 6.22 shows the distribution of the coefficient of
correlation between the envelope
()
E u
and the large-scale
L
S
fluctuations
, which is defined by
L
Λ>
1
0
(
)
(
)
⎡
⎤
uyt Euyt
+++
;
+++
;
⎣
⎦
()
()
L
L
S
[6.3]
+
R
y
=
+
+
uE u
(
)
LLS
()
2
u Eu
+
2
+
L
L
S
The correlation reaches values as high as 0.7 at the end of
the viscous sublayer, and gradually decreases, finally
disappearing entirely at
y
+
, near to the position of the
=
300
second peak
(Figure 6.20). It is interesting to
y
Λ=
0.06
0
()
()
LLS
note that
+
changes sign at
y
+
, which
R
y
>
300
+
+
uE u
indicates that the large-scale negative fluctuations
are associated with high positive values of the envelope
()
.
The rather complex behavior at the end of the boundary
layer is attributable to its intermittence. The analysis of the
experimental data in the range
E u
+
.
8
The opposite situation is true at
y
+
<
300
LS
2,800
Re
<<×
650
10
3
by
Marusic's group indicates that the position
y
+
, where the
R
=
0
()
()
LLS
correlation
+
becomes null, corresponds to the
R
y
+
+
uE u
nominal median point
y
+
of the logarithmic sublayer.
8 Which is associated with energetic values of the small-scale signal
u
+
.
S
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