Seminar Sandra Lerouge (MSC Paris)

Elastic turbulence in von Karman swirling flow of  viscoelastic fluids

Viscoelastic polymeric solutions flowing in flow geometries with curved streamlines are well known to undergo purely elastic flow instabilities with a global phenomenology reminiscent of
their Newtonian counterpart. The prototypical example is given by the Taylor-Couette flow where a succession of bifurcations is observed with increasing shear rate, from a purely azimuthal base flow to a toroidal secondary flow, followed by several space and time-dependent flow states and subsequent transition to `purely elastic turbulence’. The phenomenon of elastic turbulence was first characterized in von Karman swirling flow. The main features of this disordered flow state are a large increase of the flow resistance with a strong hysteretic character and excitation of a broad range of spatial and temporal scales leading to power law decay in the power spectra of the velocity fluctuations. Furthermore, the transition to elastic turbulence in this flow geometry is supposed to be mediated by the existence of a large toroidal vortex having the vessel size.
In this work, we propose to revisit the transition towards elastic turbulence in experimental conditions very similar to those used in the original studies. We test two types of viscoelastic systems, polymer and micelle solutions. We study the full transitional pathway from the laminar flow state to the fully developed turbulent state. The flow structure is simultaneously investigated using flow visualizations in different planes and velocimetry measurements. Our experiments reveal new findings, shaking the picture established so far.