Contact Line Instability of Gravity-Driven Flow of Power-Law Fluids

Area of Science:

• Fluid Dynamics
• Rheology
• Non-Newtonian Fluid Mechanics

Background:

• Contact line fingering instability is well-studied for Newtonian fluids but not for non-Newtonian fluids.
• The effect of shear-thinning properties on contact line instability remains largely unknown.
• Previous 2D models suggested shear-thinning reduces capillary ridge formation.

Purpose of the Study:

• To investigate how shear-thinning rheology affects the formation, growth, and shape of contact line instabilities.
• To test the hypothesis that increased shear-thinning suppresses finger growth and increases finger wavelength.
• To compare results from linear stability analysis (LSA) and 3D numerical simulations.

Main Methods:

• Developed a LSA model for gravity-driven flow of shear-thinning films.
• Conducted parametric studies on shear-thinning impact on fingering growth rates.
• Utilized fully 3D numerical simulations to verify LSA and explore multi-mode perturbations.

Main Results:

• Contact line fingers grew faster for Newtonian fluids than shear-thinning fluids on both vertical and inclined planes.
• Newtonian fluids formed shorter wavelength fingers than shear-thinning fluids on inclined planes.
• Finger spacing decreased on vertical planes compared to inclined planes for shear-thinning fluids.

Conclusions:

• Shear-thinning significantly suppresses contact line fingering instability growth.
• Results link 2D models, LSA, and 3D simulations for non-Newtonian fluid fingering.
• Findings provide insights for optimizing non-Newtonian fluid properties to minimize fingering in applications.