At finite value of the concentration, when , the
back reaction of polymers can not be neglected.
Polymers can affect
significantly the velocity dynamics, provided that they are sufficiently
elongated - a condition that is met at
.
This strong feedback regime is characterized in two dimensions by a
suppression of large-scale velocity fluctuations,
an effect first observed in soap film experiments [68].
In Figure 4.5 are reported two images of soap film experiments
from Amarouchene & Kellay. The large vortices in the polymer-free
case are strongly reduced by polymer addition. The same behavior
is observed in numerical simulations of 2D Oldroyd-B model
(Figure 4.6).
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