Flow of wormlike micellar solutions over concavities

Area of Science:

• Rheology
• Fluid Dynamics
• Soft Matter Physics

Background:

• Viscoelastic fluids exhibit complex flow behaviors, especially in geometric constrictions.
• Shear-banding wormlike micellar (WLM) solutions are model systems for studying non-Newtonian fluid dynamics.

Purpose of the Study:

• Investigate the creeping flow of viscoelastic WLM solutions over concavities of varying dimensions.
• Characterize the transition in flow regimes and vortical structures.
• Develop phase diagrams to map flow behavior against geometric parameters and viscoelasticity.

Main Methods:

• Numerical simulations using the diffusive Giesekus model.
• Experimental validation with a 100:60 mM cetylpyridinium chloride:sodium salicylate WLM solution.
• Analysis of vortical structures and flow patterns.

Main Results:

• Observed a transition from 'cavity flow' to 'expansion-contraction flow' when concavity length (L) exceeds depth (D) plus channel width (W).
• Identified distinct large-scale recirculations in cavity flow versus corner-confined recirculations in expansion-contraction flow.
• Constructed L-D phase diagrams illustrating flow transitions influenced by Weissenberg number (Wi).

Conclusions:

• Concavity geometry significantly dictates the flow regime and vortical structure of viscoelastic WLM solutions.
• The diffusive Giesekus model accurately captures the observed flow transitions and fluid behavior.
• Viscoelastic effects play a crucial role in modifying flow patterns over complex geometries.