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Accueil > Evénements > Séminaires > Archives 2009 > Exact coherent structures
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Séminaire général

Exact coherent structures and drag-reduction in Newtonian turbulence

Par : Alexander Morozov

Flows of fluids are known to become turbulent at large enough Reynolds numbers. Until now, it was virtually impossible to predict the Reynolds number of the laminar — turbulent transition or to describe flow dynamics even in the vicinity of the transition. Recently, however, it has been discovered that in simple shear flows (like pressure-driven flows in a pipe or between two plates) there exist the so-called coherent structures which organize the turbulent dynamics close to the laminar-turbulent transition. I will review the modern developments in the field and present a new theory by F.Waleffe which proposes a pictorial view of how turbulent state is constructed from coherent structures and allows one to estimate the transitional Reynolds number and many other properties of the transitional turbulent flows.

In the second part of the talk, I will present recent results on how small amounts of polymers affect turbulence — question relevant to the drag-reduction problem. I will derive a low-dimensional model for this process and discuss how coherent structures change in the presence of polymers.