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

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7 Investigation of the yz-plane
the near-wall region ¹&» Û below (see circles). Moreover it can be seen that these vortices
induce a wall-normal velocity as indicated in figure 1.3. This is fully consistent with the
results discussed in section 7.2.2. In addition the red contours, which represent a negative outof
plane velocity (ä Û fluctuation ), show that the stream-wise velocity of the fluid between
the vortex pairs is relatively low with respect to the mean motion. This implies that turbulence
is produced by these structures as expected and discussed in the previous chapters. The blue
contours indicate that the structures are frequently flanked by high-speed fluid.
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FIGURE 7.18: Velocity fluctuations (blue: 021Áž ; red: 023~ž ) with loop shaped structures, see circles.
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