General hydrodynamic features of elastoviscoplastic fluid flows through randomised porous media

TL;DR

This study numerically investigates elastoviscoplastic and viscoplastic fluids flowing through randomly constructed porous media, revealing how elasticity influences pressure drop, yielding, and flow stability across various rheological parameters.

Contribution

It introduces a comprehensive numerical analysis of elastoviscoplastic flows in porous media, highlighting the impact of elasticity on flow resistance and stability, which was not thoroughly explored before.

Findings

Elastic effects increase with Weissenberg and Bingham numbers.

Elasticity can both increase and decrease pressure drop depending on Bingham number.

Elastic stresses promote yielding and can lead to unsteady, chaotic flows.

Abstract

A numerical study of yield-stress fluids flowing in porous media is presented. The porous media is randomly constructed by non-overlapping mono-dispersed circular obstacles. Two class of rheological models are investigated: elastoviscoplastic fluids (i.e. Saramito model) and viscoplastic fluids (i.e. Bingham model). A wide range of practical Weissenberg and Bingham numbers is studied at three different levels of porosities of the media. The emphasis is on revealing some physical transport mechanisms of yield-stress fluids in porous media when the elastic behaviour of this kind of fluids is incorporated. Thus, computations of elastoviscoplastic fluids are performed and are compared with the viscoplastic fluid flow properties. At a constant Weissenberg number, the pressure drop increases both with the Bingham number and the solid volume fraction of obstacles. However, the effect of elasticity is less trivial. At low Bingham numbers, the pressure drop of an elastoviscoplastic fluid increases compared to a viscoplastic fluid, while at high Bingham numbers we observe drag reduction by elasticity. At the yield limit (i.e. infinitely large Bingham numbers), elasticity of the fluid systematically promotes yielding: elastic stresses help the fluid to overcome the yield stress resistance at smaller pressure gradients. We observe that elastic effects increase with both Weissenberg and Bingham numbers. In both cases, elastic effects finally make the elastoviscoplastic flow unsteady, which consequently can result in chaos and turbulence. Keywords: Yield-stress fluids; Viscoplastic fluids; Elastoviscoplastic fluids; Porous media