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Bifurcations in flows of complex fluids around microfluidic cylinders
Simon J Haward1, Cameron C Hopkins1, Stylianos Varchanis1
1Micro/Bio/Nanofluidics Unit, Okinawa Institute of Science and Technology, Onna, Okinawa 904-0495, Japan. simon.haward@oist.jp.
Lab on a Chip
|October 14, 2021
Summary
Flow asymmetry in microfluidic devices arises from viscoelastic effects. This study reveals a novel flow instability in slender cylinders, crucial for understanding non-Newtonian fluid behavior in microscale applications.
Area of Science:
- Fluid dynamics
- Microfluidics
- Non-Newtonian fluid mechanics
Background:
- Flow around a cylinder is a benchmark for testing viscoelastic flows.
- Relevant to microscale industrial and biological processes like porous media and mucociliary flows.
Purpose of the Study:
- Investigate flow instability in microfluidic geometries with slender cylinders.
- Understand the mechanism of flow asymmetry in viscoelastic fluids.
Main Methods:
- Fabrication of slender cylinders in glass using selective laser-induced etching.
- Testing various viscoelastic fluids (wormlike micellar, polymer solutions).
- Utilizing high aspect ratio microchannels for approximately 2D flow fields.
Main Results:
- Observed a striking, steady-in-time flow asymmetry for certain non-Newtonian fluids.
- Flow asymmetry occurs when the dimensionless Weissenberg number exceeds a critical value.
- Identified a novel flow instability driven by viscoelastic forces.
Conclusions:
- The fundamental mechanism may explain phenomena in viscoelastic flows around particles, drops, bubbles, and porous media.
- Understanding this instability is vital for designing lab-on-a-chip devices using viscoelastic fluids.
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