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

6.4 Properties of coherent velocity structures
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FIGURE 6.23: Velocity fluctuations measured at Ó ® óÜ Ø
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complexity of the turbulent motion and the limitations of the measurement techniques the
cause and dynamic is still the subject of controversial discussions. In order to investigate this
exchange processes in detail, the interaction of the streaks with the surrounding fluid will be
investigated next. Especially the interaction regarding the high momentum flow structures
which move towards the wall will be considered, as only these possess the energy required to
alter the turbulence structure of the flow field effectively.
It is evident that the high-momentum flow structures must be visible in nearly each velocity
field in order to compensate the low-momentum movement of the streaks, but in contrast
to the low-speed streaks the variety of these structures is much larger. Usually they appear
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