The significance of coherent flow structures for the turbulent mixing ...

6 Investigation of the xz-plane
300
250
Q2
200
z
+
150
100
Q2
50
Q2
300
0
0 50 100 150 200 250 300 350 400 450 500 550
??]
x [???]
250
200
Q2
Q2
Q4
Q2
z
+
150
Q2
100
50
Q2
Q4
0
0 50 100 150 200 250 300 350 400 450 500 550
FIGURE 6.22: Velocity fluctuations measured at Ó ® Ú¥Ø
(red: C_ Ø
; blue: CG! Ø
).
x
+
??]
x [???]
Ñ Ë correlation in figure 6.8 and 6.9 and implies that no pairs of stream-wise counter-rotating
Ã
vortices flank the low-speed regions over their total length, as proposed by some authors [54].
Otherwise, one would expect to detect a sign change in the out-of-plane motion on both sides
of the streaks or at least a large variation over the length of the streaks.
·
6.4.2 Sweeps
The production of turbulence caused by the lifting of the low-speed streaks is one of the
basic processes identified in near-wall turbulence as already mentioned. However, due to the
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