Turbulence in polymer solutions

The presence of minute long-chain polymers in a flow may strongly change the flow. At very low Reynolds numbers it gives rise to the interesting behaviour of elastic turbulence[1] and may enhance mixing[2]. At high Reynolds numbers introducing polymers into wall-bounded flows can lead to the fascinating drag reduction phenomenon, whch is a subject of intense current interest (see [3] for a recent review).

Using three-dimensional particle tracking, we are currently studying the effect of polymers on bulk turbulence at high Reynolds numbers far away from the boundary. The turbulence is generated by a von Kármán swirling water flow between counter-rotating baffled disks. Experiments are also performed in the Lagrangian Exploration Module (LEM), where the turbulence is more homogeneous and isotropic.

For Newtonian turbulence, most of our understanding comes from the Richardson-Kolmogorov energy cascade hypothesis[4] which states that the energy injected at large length scales is transferred to smaller length scales until it is dissipated at the smallest length scales where viscosity acts. This classical picture is not valid in the presence of polymeric additives. When stretched by the flow, polymer chains are able to store energy and can release it into the flow when stretching forces become smaller. There will also be losses of kinetic energy this stretching-recoiling process. Thus, polymer chains introduce new energy transfer and energy dissipation mechanisms into the flow, which can be very important even in a very dilute régime.

To determine the importance of elasticity we use different polymers and change fluid properties by adding other agents. We also carry out micro-scale measurements to characterise the alignment and the elongation of fluorescently dyed polymers in the turbulent flow.

Contact: Eberhard Bodenschatz

[1] A. Groisman and V. Steinberg, Nature, 405, 53 (2000)
[2] A. Groisman and V. Steinberg, Nature, 410, 905 (2001)
[3] I. Procaccia, V. L'vov, R. Benzi, Rev. Mod. Phys., 80, 225 (2008)
[4] А. Н. Колмогоров, Доклады АН СССР, 30, 299-303 (1941), English translation: A. N. Kolmogorov, Proc. R. Soc. A, 434, 9-13 (1991)