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

6 Investigation of the xz-plane
300
250
200
Vortex pair
z
+
150
Vortex pair
Vortex pair
100
50
0
0 50 100 150 200 250 300 350 400 450 500 550
300
250
??]
x [???]
z
+
200
150
Q2
Q2
Q4
Q2
100
Q2
50
Q4
0
0 50 100 150 200 250 300 350 400 450 500 550
x
+
y [???]
x [???]
FIGURE 6.27: Velocity fluctuations measured at Ó ® Ú¥Ø
(top) and Reynolds stress component &C
(bottom).
tic velocity pattern, the velocity structure of the PIV measurements is analysed in stream-wise
direction for various span-wise locations. For the comparison it is important to keep in mind
that in the PIV experiment the spatial variation of the velocity is considered at a fixed time
while the time signal of the velocity is considered at a fixed point in the hot wire investigation.
The left image of figure 6.30 shows three typical instantaneous signals of the § -velocity
component which nicely matches with the ensemble averaged pattern deduced from the hot
wire measurements. The signals were extracted from figure 6.28 along the red lines located
at Ï ® ¿ ÈÀ , 120 and 220. It can be clearly seen that the characteristic velocity pattern is
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