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

7.5 Properties of coherent velocity structures
assumed to be universal and thus independent on the magnitude of /. äŸã , it is evident that their
geometrical and dynamical properties can be best examined when the effect of the background
turbulence, which often deteriorates the analysis of the less intense structures, becomes small
in relation to the structures under investigation. Figure 7.20 shows two samples measured
independently ª«§_¬ ®w¯ at . Clearly visible in both velocity fields is the high-momentum
large-scale motion (blue), which moves towards the wall, and the effect when these structures
interact in the near-wall region with the low-momentum structures (red).
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FIGURE 7.21: Same as figure 7.18 but measured simultaneously at spatially separated (É ¨ » š
planes
) to examine the length of the stream-wise vortices in ¨ -direction.
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