Wall Effects for Spheroidal Particle in Confined Bingham Plastic Fluids

Area of Science:

• Fluid Dynamics
• Rheology
• Particle Sedimentation

Background:

• Understanding particle motion in non-Newtonian fluids is crucial for industrial processes.
• Bingham plastic fluids exhibit a yield stress, complicating sedimentation dynamics.
• Wall effects in confined geometries significantly alter particle behavior.

Purpose of the Study:

• To investigate the wall effects on the sedimentation of a single spheroidal particle in Bingham plastic fluid.
• To analyze the influence of Reynolds number, radius ratio, aspect ratio, and Bingham number on particle motion.
• To validate a Computational Fluid Dynamic (CFD) model for this complex flow scenario.

Main Methods:

• A fixed computational domain was used with a Computational Fluid Dynamic (CFD) model in steady-state mode.
• The Bingham plastic rheological model was regularized using smoothly varying viscosity.
• The CFD model was validated against existing literature for both bounded and unbounded mediums.

Main Results:

• The drag coefficient decreases with increasing Reynolds number.
• Higher Bingham numbers increase the contribution of pressure force to drag compared to friction force.
• Yield stress suppresses recirculation wake formation and size; wall influence becomes negligible for radius ratios > 5 when Bingham number ≥ 100.

Conclusions:

• The study quantifies wall retardation effects on particle sedimentation in Bingham plastics.
• Critical yield-gravity parameters were determined, showing independence from Reynolds number and radius ratio for specific aspect ratios.
• CFD modeling provides a robust method for analyzing particle dynamics in complex non-Newtonian fluids.