PhD project: Purely Elastastic Instabilities and Turbulence

Project description

Solutions of long flexible polymer molecules do not flow like water. A classical example of such a strange behaviour is observed when a rod is rotated in a polymer solution -- the fluid tends to climb the rod! This behaviour is caused by the flow-induced stretching and orientation of polymer molecules, which in turn results in large anisotropic elastic stresses in the solution. Typically polymer solutions are very viscous and flow slowly, and, therefore, will not exhibit inertial hydrodynamic instabilities and turbulence typical for water.

Unexpectedly, it was recently discovered that polymeric flows do become unstable but these instabilities are instead caused by anisotropic elastic stresses due to polymer stretching. Even more surprisingly, at higher flow rates (but still flowing very slowly!) the flow becomes chaotic and exhibits turbulent-like features at, essentially, zero Reynolds numbers [1,2]. The mechanism of this new type of chaotic motion - the so-called purely elastic turbulence - is presently not understood. You will employ direct numerical simulations to uncover the physical origins of purely elastic instabilities and turbulence in various flows.

[1] Turbulence without inertia, R. G. Larson, Nature 405, 27 (2000).

[2] An introductory essay on subcritical instabilities and the transition to turbulence in visco-elastic parallel shear flows, A. N. Morozov and W. van Saarloos, Physics ReportsĀ  447, 112 (2007).

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