Elastic instabilities in straight channel: An increase of apparent viscosity
Abstract
Polymeric solutions are viscoelastic: they are characterized by a relaxation time-that is the time required by the polymer molecules to adjust to changes in the flow conditions. The existence of this characteristic time is at the origin of purely elastic instabilities which are observed at very low Reynolds numbers and do not have their counter part in pure Newtonian fluids. The instability threshold depends on the curvature of the streamlines. These flows are linearly unstable in curved geometry and stable in straight channels. In this work, we revisit this question and display a comprehensive picture of the flow in those systems in straight geometries. Using state to the art microfluidic techniques, we measure the entire velocity profile and extract the local flow curve, the slip velocity and analyze their dynamics. Our main originality is to show the impact of the elastic instability in straight channel on the rheological behavior, to point out the turbulent nature of the flow and to evidence the common features sheared by the elastic and by the inertial turbulence.
- Publication:
-
APS Division of Fluid Dynamics Meeting Abstracts
- Pub Date:
- November 2013
- Bibcode:
- 2013APS..DFDL11006C