Three-dimensional structures and symmetry breaking in viscoelastic cross-channel flow

Area of Science:

• Fluid Dynamics
• Rheology
• Non-Newtonian Flows

Background:

• Viscoelastic instabilities are crucial in microfluidic devices and polymer processing.
• Understanding the 3D flow dynamics is key to controlling these instabilities.
• Previous studies often lacked detailed 3D structural information.

Purpose of the Study:

• To elucidate the three-dimensional flow structure of viscoelastic instability in cross-channel flow.
• To identify the onset and characteristics of tertiary flow.
• To investigate the relationship between flow structure and symmetry breaking.

Main Methods:

• Holographic particle tracking velocimetry (HPV) for high-resolution 3D velocity measurements.
• Cross-channel flow geometry to study impinging viscoelastic streams.
• Varying the Weissenberg number (Wi) to probe instability regimes.

Main Results:

• Observed emergence of tertiary flow beyond a critical Wi, forming toroidal vortices.
• Identified out-of-plane flow component distorting the flow separatrix.
• Demonstrated symmetry breaking normal to the extension plane.
• Noted propagation of disturbances upstream via stress fluctuations.

Conclusions:

• The study reveals complex 3D flow structures organizing viscoelastic instability.
• Observed phenomena, including symmetry breaking and upstream disturbance propagation, offer insights into elastic turbulence.
• These findings may be generalizable to other mixed viscoelastic flows.