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Active polymers

At finite value of the concentration, when $\eta > 0$, 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 $Wi > 1$. 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).

Figure 4.5: Interferograms of the thickness field of a soap film in the polymer-free case (left) and viscoelastic case (right). Y. Amarouchene, H. Kellay, Phys. Rev. Lett. 89, 104502 (2002)
\includegraphics[draft=false, scale=0.75, clip=true]{P_amarouch1.eps} \includegraphics[draft=false, scale=0.75, clip=true]{P_amarouch2.eps}
Figure: Snapshots of the vorticity field ${\mbox{\boldmath $\nabla$}} \times {\mbox{\boldmath $u$}}$ in the Newtonian (left) and in the viscoelastic case with strong feedback (right). Notice the suppression of large-scale structures in the latter case.
\includegraphics[draft=false, scale=0.7, clip=true]{P_newton.eps} \includegraphics[draft=false, scale=0.7, clip=true]{P_visco.eps}



Subsections
next up previous contents
Next: Depletion of kinetic energy Up: Two-dimensional turbulence of dilute Previous: Stretched state   Contents
Stefano Musacchio 2004-01-09