Perspectives on viscoelastic flow instabilities and elastic turbulence

Abstract

Viscoelastic fluids are a common subclass of rheologically complex materials that are encountered in diverse fields from biology to polymer processing. Often the flows of viscoelastic fluids are unstable in situations where ordinary Newtonian fluids are stable, owing to the nonlinear coupling of the elastic and viscous stresses. Perhaps more surprisingly, the instabilities produce flows with the hallmarks of turbulence-even though the effective Reynolds numbers may be O(1) or smaller. We provide perspectives on viscoelastic flow instabilities by integrating the input from speakers at a recent international workshop: historical remarks, characterization of fluids and flows, discussion of experimental and simulation tools, and modern questions and puzzles that motivate further studies of this fascinating subject. The materials here will be useful for researchers and educators alike, especially as the subject continues to evolve in both fundamental understanding and applications in engineering and the sciences.I.

Upstream wall vortices in viscoelastic flow past a cylinder

“…3D numerical simulations of viscoelastic flow past a cylinder, and a systematic experimental study that varies the channel blockage and aspect ratios, and the rheology of the test fluid will be instructive. Our results contribute to the rapidly growing understanding viscoelastic flow instabilities in microfluidic geometries, 15,24,57 and should be considered in the design of microfluidic devices and lab-on-a-chip systems that utilize viscoelastic fluids.…”

“…Such flows are prone to instability in a variety of different geometries, driven entirely by elastic effects. 4,[7][8][9][10][11][12][13][14][15] These elastic instabilities can affect widespread industrially and biologically relevant processes such viscoelastic flow in porous media, [16][17][18][19][20][21][22][23][24] hemodynamics, [25][26][27] and jet fragmentation. 28,29 A common morphological structure that appears due to elastic instability is the formation of a vortex, or vortices, upstream of a geometric feature in a channel.…”

“…Such flows are prone to instability in a variety of different geometries, driven entirely by elastic effects. 4,7–15 These elastic instabilities can affect widespread industrially and biologically relevant processes such viscoelastic flow in porous media, 16–24 hemodynamics, 25–27 and jet fragmentation. 28,29…”

Effects of vertical confinement on the flow of polymer solutions in planar constriction microchannels

“…Flow of polymer solutions through extensional microstructures, where the cross-sectional area changes along the length of the fluid passage, can induce non-linear viscoelastic responses. [1][2][3] Such scenarios are frequently encountered in many engineering fields such as petroleum engineering, groundwater remediation, point-of-care diagnostics, etc. [4][5][6][7] Understanding the nature of polymer flows in contraction and/or expansion microchannels thus becomes important in making the performance and design decisions.…”

“…These solutions are noted to have been frequently used for industrial and microfluidic applications. [3][4][5][6][7][8]18,19,27 They are each tested along with water from the non-inertial to inertia-dominated flow regime in every channel for a systematic understanding of both the sole and combined effects of fluid shear thinning, elasticity and inertia on the channel depth-dependent instabilities. Small fluorescent particles are seeded into each of the prepared solutions for a direct visualization of the flow pattern in the contraction-expansion region of the microchannels.…”