Journal
JOURNAL OF FLUID MECHANICS
Volume 950, Issue -, Pages -Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/jfm.2022.836
Keywords
microscale transport; viscoelasticity; porous media
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Funding
- OIST
- Cabinet Office, Government of Japan
- Japanese Society for the Promotion of Science (JSPS) [21K14080, 21K03884]
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This study investigates the phenomenon of elastic turbulence and its effects on the flow state of polymer chains and flow fields. By conducting experimental observations and analysis on the flow in a three-dimensional ordered porous medium, it is found that elastic turbulence can be triggered when specific parameters exceed a critical value. In the state of elastic turbulence, polymer chains are influenced by the curvature of the flow streamline, leading to flow instability.
Viscoelastic flow instability, which is compelled by elastic effects rather than inertia, can be driven to a chaotic state termed elastic turbulence (ET) manifested as strong velocity fluctuations with an algebraic decay in the frequency spectrum and increased mixing. We report the first spatiotemporally complete description of ET by considering a broad volume within a novel three-dimensional ordered porous medium, reconstructing flow at a micrometre characteristic length scale (Reynolds numbers << 1) via time-resolved microtomographic particle image velocimetry. Beyond a critical Weissenberg number of 2, we observe an elastic flow instability accompanied by an enhanced pressure drop with spectral characteristics typical of ET. Polymer chains in the ET flow state are advected along increasingly curved streamlines between pores such that they accumulate strain and generate a local flow instability evaluated per an established instability criterion based on local evaluation of elastic tensile stress and streamline curvature. The onset of ET leads to increased pore-scale resistance and positive feedback on upstream streamline curvature. ET is thus characterized by a continuous evolution between states of laminar and unstable flow: pores with unstable flow flood their adjacent peers and thus encourage straightened streamlines and flow stability across the array, while positive feedback from flow resistance on streamline curvature results in the instability propagating upstream along the array. By employing a geometrically ordered medium, we permit flow state communication between pores, yielding generalized insights highlighting the significance of spatial correlation and flow history, and thus provide new avenues for explaining the mechanisms of ET.
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