Kinetic zero-average contrast

This kinetic zero average contrast (KZAC) experiment [100-102] is an extension to the static zero average contrast (ZAC) described in Sect. 3.1.7. ZAC is used to effectively remove the structure factor such that interparticle correlations are eliminated and the single entities are visible, whereas in KZAC the trick is used to render mixing processes hence, diffusion and transport become observable without perturbing the system in any substantial way. 

Recall our short discussion in Section 18.5 where we learned that turbulence is kind of an analytical trick introduced into the theory of fluid flow to separate the large-scale motion called advection from the small-scale fluctuations called turbulence. Since the turbulent velocities are deviations from the mean, their average size is zero, but not their kinetic energy. The kinetic energy is proportional to the mean value of the squared turbulent velocities, Mt2urb, that is, of the variance of the turbulent velocity (see Box 18.2). The square root of this quantity (the standard deviation of the turbulent velocities) has the dimension of a velocity. Thus, we can express the turbulent kinetic energy content of a fluid by a quantity with the dimension of a velocity. In the boundary layer theory, which is used to describe wind-induced turbulence, this quantity is called friction velocity and denoted by u. In contrast, in river hydraulics turbulence is mainly caused by the friction at the... 

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