Disorder Suppresses Chaos in Viscoelastic Flows

Abstract

Viscoelastic flows transition from steady to time-dependent, chaotic dynamics under critical flow conditions, but the implications of geometric disorder for flow stability in these systems are unknown. Utilizing microfluidics, we flow a viscoelastic fluid through arrays of cylindrical pillars, which are perturbed from a hexagonal lattice with various degrees of geometric disorder. Small disorder, corresponding to ∼ 10% of the lattice constant, delays the transition to higher flow speeds, while larger disorders exhibit near-complete suppression of chaotic velocity fluctuations. We show that the mechanism facilitating flow stability at high disorder is rooted in a shift from extension-dominated to shear-dominated flow type with increasing disorder.

Shear-thinning mediation of elasto-inertial Taylor–Couette flow

“…Moreover, the strength of the extensional deformations induced by such perturbations would be reduced compared with the dominant radial shear rate, which is also in turn enhanced by the radial viscosity distribution. An analogy to this mechanism can be found in the recent work by Walkama, Waisbord & Guasto (2020), who performed an experimental study of the onset of elastic instabilities (at vanishing ) in a microfluidic flow of PEO-based Boger fluids past an array of cylinders. Spatial disorder was found to delay or even suppress the onset of elastic instability.…”

Active open-loop control of elastic turbulence

“…For example, in Ref. 31 , geometric disorder is introduced in a microfluidic flow, which leads to a disordered local shear rate and thereby delays the occurence of elastic turbulence to larger Wi. This corresponds to spatial shear rate modulations, where increased disorder is equivalent to faster modulations.…”

“…Both control schemes applied to flow patterns and fluid instabilities in Newtonian fluids have extensively been studied [18][19][20][21][22][23][24][25] . Also, passive control of viscoelastic fluid flow has been examined [26][27][28][29][30][31] using either geometric modifications 28,29 including spatially modulated cylinders in a Taylor-Couette geometry 30 and disorder in microfluidic flows to inhibit elastic turbulence 31 , or soft boundaries 27 , as well as thermal control 26 . In contrast, the search for active control strategies appropriate for viscoelastic fluids has so far been limited.…”

Localization in Flow of Non-Newtonian Fluids Through Disordered Porous Media

“…It has a shear-thinning rheology which changes its apparent viscosity over several orders of magnitude. While polymeric solutions often show viscoelastic behavior [51], the concentration of xanthan gum in our experimental solution was so low that no measurable elastic behavior could be observed during the experiment. The rheology of xanthan gum closely follows a Carreau model,…”