Effect of blockage ratio on flow of a viscoelastic wormlike micellar solution past a cylinder in a microchannel.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 36374283.
- Also identified by DOI 10.1039/d2sm01162j and PMC identifier 9709659.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
We present experiments on the flow of a viscoelastic wormlike micellar solution around cylinders (radius <i>R</i>) confined in straight microchannels (width <i>W</i>). Thirteen flow geometries are tested where the blockage ratio is varied over a wide range 0.055 ≤ <i>B</i><sub>R</sub> = 2<i>R</i>/<i>W</i> ≤ 0.63. Experiments are performed at negligible Reynolds number, and for Weissenberg numbers <i>Wi</i> = <i>λU</i>/<i>R</i> up to 1000, where <i>U</i> is the average flow speed and <i>λ</i> is the relaxation time of the fluid. Micro-particle image velocimetry is used to characterise the flow state at each <i>B</i><sub>R</sub> and <i>Wi</i>. In all of the geometries, a first critical Weissenberg number marks a transition from symmetric flow to an asymmetric but time-steady flow state, while a second higher critical Weissenberg number marks the onset of time-dependent flows. However, we report a clear shift in behaviour over a narrow intermediate range of 0.33 ≲ <i>B</i><sub>R</sub> ≲ 0.41. Channels with <i>B</i><sub>R</sub> ≤ 0.33 fall in a 'low' <i>B</i><sub>R</sub> regime, with instabilities that originate from the downstream stagnation point, while those with <i>B</i><sub>R</sub> ≥ 0.44 fall in a 'high' BR regime, with instabilities developing at the upstream stagnation point. Behaviour within the newly-identified intermediate <i>B</i><sub>R</sub> regime is complex due to the competing influence of the two stagnation points. We summarise all our results in a flow state diagram covering <i>Wi</i>-<i>B</i><sub>R</sub> parameter space, clearly defining the different regimes of blockage ratio for the first time. Our results contribute to the understanding of the complexities of viscoelastic flow in this benchmark geometry.