Elastic Instabilities in Flows through Pillared Micro channels

TL;DR

This study reveals novel elastic instabilities in viscoelastic fluids flowing through pillared microchannels, characterized by large lateral excursions and flow asymmetries at low Reynolds numbers, driven by the interplay of pore structure and fluid rheology.

Contribution

It provides the first experimental evidence of elastic instabilities in porous media flows, highlighting unique flow behaviors not previously reported in simple shear or curved flows.

Findings

Observation of large lateral excursions and flow lanes.

Transition from symmetric to asymmetric and nonlinear flow.

Instabilities occur at very low Reynolds number (< 0.01).

Abstract

Viscoelastic fluids exhibit elastic instabilities in simple shear flow and flow through curved streamlines. Surprisingly, we found in a porous medium such fluids show strikingly different hydrodynamic instabilities depicted by very large sideways excursions and presence of fast and slow moving lanes which have not been reported before. Particle image velocimetry (PIV) measurements through a pillared microchannel, provide experimental evidence of such instabilities at very low Reynolds number (< 0.01). We observe a transition from a symmetric laminar to an asymmetric flow, which finally transforms to a nonlinear aperiodic flow with strong lateral movements. The instability is characterized by a rapid increase in spatial and temporal fluctuations of velocity components and pressure at a critical Deborah number (De). Our experiments reveal the presence of a fascinating interplay between pore space and fluid rheology.