Start-up inertia as an origin for heterogeneous flow.

Area of Science:

• Rheology and Complex Fluids
• Computational Fluid Dynamics
• Material Science

Background:

• Shear banding in complex fluids was traditionally linked to nonmonotonic flow curves.
• Simple yield stress fluids were thought to lack shear banding due to monotonic flow curves.
• Recent experiments revealed shear banding in simple yield stress fluids, prompting new mechanistic explanations.

Purpose of the Study:

• To investigate the mechanisms initiating transient shear banding in simple yield stress fluids.
• To determine if fluid inertia during start-up can trigger shear banding under homogeneous stress conditions.
• To assess the relevance of inertial effects in realistic experimental setups.

Main Methods:

• Computational fluid dynamics (CFD) simulations were employed.
• The study focused on fluid start-up dynamics.
• Simulations considered homogeneous stress conditions and realistic experimental geometries.

Main Results:

• Transient shear banding can be initiated by fluid start-up inertia, even without initial stress heterogeneity.
• Inertial effects provide a viable mechanism for transient shear banding in simple yield stress fluids.
• This inertial mechanism is relevant under conditions mimicking real-world experiments.

Conclusions:

• Fluid start-up inertia is a key factor in initiating transient shear banding in simple yield stress fluids.
• The traditional requirement of nonmonotonic flow curves for shear banding is challenged.
• This work offers a new perspective on the rheological behavior of yield stress fluids.