Stress and stretching regulate dispersion in viscoelastic porous media flows

TL;DR

This study investigates how viscoelastic instability influences fluid dispersion in porous media, revealing that flow order and instability significantly affect transverse and longitudinal dispersion through experimental and simulation analysis.

Contribution

It demonstrates the impact of viscoelastic instability on dispersion in porous media and highlights the role of flow order and Lagrangian structures in transport behavior.

Findings

Viscoelastic instability enhances transverse dispersion in ordered media.

Disordered media with flow paths suppress elastic instability, reducing transverse dispersion.

Flow along preferential paths increases longitudinal dispersion with higher Weissenberg numbers.

Abstract

In this work, we study the role of viscoelastic instability in the mechanical dispersion of fluid flow through porous media at high Peclet numbers. Using microfluidic experiments and numerical simulations, we show that viscoelastic instability in flow through a hexagonally ordered (staggered) medium strongly enhances dispersion transverse to the mean flow direction with increasing Weissenberg number (Wi). In contrast, preferential flow paths can quench the elastic instability in disordered media, which has two important consequences for transport: First, the lack of chaotic velocity fluctuations reduces transverse dispersion relative to unstable flows. Second, the amplification of flow along preferential paths with increasing Wi causes strongly-correlated stream-wise flow that enhances longitudinal dispersion. Finally, we illustrate how the observed dispersion phenomena can be understood through the lens of Lagrangian stretching manifolds, which act as advective transport barriers and coincide with high stress regions in these viscoelastic porous media flows.