Canopy elastic turbulence: spontaneous formation of waves in beds of slender microposts

TL;DR

This paper reports the discovery of spontaneous wave formations in viscoelastic microfluidic flows over flexible micropost canopies, exhibiting characteristics of elastic turbulence and coupling between flow and canopy deformation.

Contribution

It introduces the phenomenon of canopy elastic turbulence, demonstrating wave formation and flow-structure interactions in viscoelastic microfluidic canopies, a novel observation in this context.

Findings

Waves form at an angle depending on pillar array geometry

Flexible structures are deflected by passing waves

Wave behavior resembles inertial turbulence over vegetation canopies

Abstract

In a viscoelastic flow over a microfluidic canopy of polymeric pillars, we report the spontaneous emergence of waves in the form of propagating regions of low flow velocity compared to the surrounding flow. The occurrence of the wave is chaotic and shows characteristics of elastic turbulence. We systematically study the coupling between the low velocity wave and the microfluidic canopy by combining flow velocimetry experiments and high speed tracking of the pillars. The waves form an angle $\beta$ with the primary flow direction that depends on the geometry of the pillar array. If the canopy is composed of flexible structures, the passage of a wave deflects the structures locally in a manner reminiscent of the emergence of the Monami waves observed in inertial turbulence over canopies of vegetation. Due to the analogies with classical (inertial) canopy turbulence, we name our newly-observed phenomenon as canopy elastic turbulence.