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

7.4 Spatio-temporal correlations with çéè
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7 Investigation of the yz-plane
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In this section various one-dimensional spatio-temporal correlation functions calculated from
measurements in spatially separated planes will be examined. This particular experimental arrangement
allows to select a flow pattern at an upstream position and to measure the structural
changes due to the mean velocity gradients and to the turbulent motion as a function of the
spatial distance between the light-sheet pairs and the time delay between the measurements.
Figure 7.15 to figure 7.17 reveal the primary correlation functions for various wall distances
from the fixed point and time delays between the measurements. The results were obtained
by cross-correlating the measurements acquired at different locations (325 wall-units streamwise
separation between both measurement planes) while the downstream measurement was
performed after the upstream measurement as indicated by the axis label. As the local mean
velocity is approximately ¿ ä » according to figure 7.3, the structures selected at the upstream
1
1
0.8
0.8
R uu
(∆t + =0)
0.6
0.4
0.2
R uu
(∆t + =20)
0.6
0.4
0.2
0
1
£
0
100
£
200
£
y + +∆y +
300
£
400
£
500
£
0
1
£
0
100
£
200
£
y + +∆y +
300
£
400
£
500
£
0.8
0.8
R uu
(∆t + =8)
0.6
0.4
0.2
R uu
(∆t + =25)
0.6
0.4
0.2
0
1
£
0
100
£
£
200 300
y + +∆y + ¤
400
£
500
£
0
1
£
0
100
£
£
200 300
y + +∆y + ¤
400
£
500
£
0.8
0.8
R uu
(∆t + =15)
0.6
0.4
0.2
R uu
(∆t + =30)
0.6
0.4
0.2
0
£
0
100
£
200
£
y + +∆y +
300
£
400
£
500
£
0
£
0
100
£
200
£
y + +∆y +
300
£
400
£
500
£
FIGURE 7.15: ˜ ·· correlation measured at ˜ášLœ§§žž and © » š
location of the maximum) for various temporal delays (see axis label).
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