Mixing layer instability and vorticity amplification in a creeping viscoelastic flow

Abstract

We report quantitative evidence of mixing-layer elastic instability in a viscoelastic fluid flow between two widely spaced obstacles hindering a channel flow at $Re\ll 1$ and $Wi\gg 1$. Two mixing layers with nonuniform shear velocity profiles are formed in the region between the obstacles. The mixing-layer instability arises in the vicinity of an inflection point on the shear velocity profile with a steep variation in the elastic stress. The instability results in an intermittent appearance of small vortices in the mixing layers and an amplification of spatio-temporal averaged vorticity in the elastic turbulence regime. The latter is characterized through scaling of friction factor with $Wi$, and both pressure and velocity spectra. Furthermore, the observations reported provide improved understanding of the stability of the mixing layer in a viscoelastic fluid at large elasticity, i.e. $Wi\gg 1$ and $Re\ll 1$, and oppose the current view of suppression of vorticity solely by polymer additives.

arXiv comment6 pages, 7 figures

References in corpus (7)

• Elastic turbulence in a polymer solution flow
• Efficient Mixing at low Reynolds numbers using polymer additives
• Elastic turbulence in curvilinear flows of polymer solutions
• Spectra of turbulence in dilute polymer solutions
• Elastic turbulence in von Karman swirling flow between two disks
• Elastic wake instabilities in a creeping flow between two obstacles
• Elastic turbulence in a curvilinear channel flow

Cited by in corpus (7)

• The center-mode instability of viscoelastic plane Poiseuille flow
• A continuous pathway between the elasto-inertial and elastic turbulent states in viscoelastic channel flow
• Elastic Alfven waves in elastic turbulence
• Elastically driven Kelvin-Helmholtz-like instability in planar channel flow
• New directions and perspectives in elastic instability and turbulence in various viscoelastic flow geometries without inertia
• Re-laminarization of elastic turbulence
• Pressure measurements in an elastically turbulent co-moving Kelvin-Helmholtz-like shear flow inside a straight Hele-Shaw cell