Characterizing Elastic Turbulence in Channel Flows at Low Reynolds number

TL;DR

This paper experimentally explores elastic turbulence in viscoelastic channel flows at low Reynolds number, revealing nonlinear instabilities and contrasting flow behaviors with cylinder flows, and proposes a mechanism based on polymer stretching.

Contribution

It provides the first detailed experimental characterization of elastic turbulence in parallel shear flows at low Reynolds number and compares it with flow around cylinders, highlighting key differences.

Findings

Elastic turbulence exhibits broad-spectrum velocity fluctuations.

Flow around cylinders shows different spectral and flow structure characteristics.

Polymer stretching due to velocity gradient fluctuations explains velocity fluctuation growth.

Abstract

We experimentally investigate the flow of a viscoelastic fluid in a parallel shear geometry at low Reynolds number. As the flow becomes unstable via a nonlinear subcritical instability, velocimetry measurements show non-periodic fluctuations over a broad range of frequencies and wavelengths, consistent with the main features of elastic turbulence. Using the same experimental setup, we compare these features to those in the flow around cylinders, which is upstream to the parallel shear region; we find significant differences in power spectra scaling, intermittency statistics, and flow structures. We propose a simple mechanism to explain the growth of velocity fluctuations in parallel shear flows based on polymer stretching due to fluctuations in streamwise velocity gradients.