Wake asymmetry weakening in viscoelastic fluids: Numerical discovery and mechanism exploration

TL;DR

This study uses numerical simulations to demonstrate that viscoelastic fluids reduce wake asymmetry behind blunt bodies by forming a symmetric elastic stress shield, restoring flow symmetry at high Weissenberg numbers.

Contribution

The paper provides the first numerical evidence and mechanistic explanation for wake symmetry restoration in viscoelastic flows around various blunt bodies.

Findings

High elastic stress regions form in front of blunt bodies at high Weissenberg numbers.

These regions act as shields, restoring flow symmetry behind the bodies.

Viscoelasticity weakens flow asymmetry in multiple configurations.

Abstract

Viscoelasticity weakens the asymmetry of laminar shedding flow behind a blunt body in a free domain. In the present study, this finding is confirmed by four unsteady viscoelastic flows with asymmetric flow configuration, i.e., flow over an inclined flat plate with various angles of incidence, flow over a rotating circular cylinder, flow over a circular cylinder with asymmetric slip boundary distribution, and flow over an inclined row of eight equally closely spaced circular cylinders (which can be considered as a single large blunt body) through direct numerical simulation combined with the Peterlin approximation of the finitely extensible nonlinear elastic (FENE-P) model. At high Weissenberg number, an arc shape region with high elastic stress, which is similar to shock wave, forms in the frontal area of the blunt body. This region acts as a stationary shield to separate the flow into different regions. Thus, the free stream resembles to pass this shield instead of the original blunt body. As this shield has symmetric feature, the wake flow restores symmetry.