Capsules Rheology in Carreau-Yasuda Fluids

Area of Science:

• Computational Fluid Dynamics
• Non-Newtonian Fluid Mechanics
• Biophysics

Background:

• Accurate simulation of non-Newtonian fluids with immersed objects is crucial for understanding complex fluid dynamics.
• Existing models often simplify fluid behavior, necessitating advanced numerical methods for shear-dependent viscosity.
• The interaction between fluid rheology and immersed body dynamics requires detailed investigation.

Purpose of the Study:

• To develop and validate a computational model for simulating non-Newtonian fluid flow with immersed bodies.
• To analyze the influence of shear-dependent viscosity on flow patterns and immersed capsule behavior.
• To investigate capsule revolution and equilibrium positions in various non-Newtonian fluids.

Main Methods:

• Employed a Multi Relaxation Time Lattice Boltzmann scheme coupled with an Immersed-Boundary technique.
• Imposed no-slip boundary conditions on immersed bodies via a forcing term accounting for hydrodynamic and viscosity forces.
• Validated the model against benchmarks: flow in laminae and lid-driven cavity flow; analyzed capsule dynamics in Couette flow.

Main Results:

• The model accurately reproduces parabolic velocity profiles for varying viscosity exponents (n).
• In shear-thinning fluids, viscosity reduction in high-shear zones shifts minima towards lateral walls.
• Capsule revolution periods and tumbling inhibition (at critical Re) are consistent with existing models across different fluid types (shear-thinning, Newtonian, shear-thickening).

Conclusions:

• The developed numerical scheme effectively captures non-Newtonian fluid behavior and its interaction with immersed objects.
• Shear-dependent viscosity significantly influences flow fields and capsule dynamics.
• The study confirms the applicability of established capsule dynamics laws to non-Newtonian environments.