Hydrodynamic Behavior of Self-Propelled Particles in a Simple Shear Flow

Area of Science:

• Fluid Dynamics
• Soft Matter Physics
• Computational Physics

Background:

• Self-propelled particles, like squirmers, exhibit complex behaviors in fluid environments.
• Understanding their hydrodynamic properties is crucial for applications in microfluidics and biological systems.
• Previous studies have explored squirmer dynamics, but comprehensive analysis across various flow regimes is ongoing.

Purpose of the Study:

• To investigate the hydrodynamic properties of a squirmer particle in a simple shear flow.
• To analyze the influence of swimming Reynolds number (Re), flow Reynolds number (Re), and wall interaction (κ) on squirmer motion.
• To identify and characterize distinct motion modes of the squirmer under varying conditions.

Main Methods:

• Utilized the immersed boundary-lattice Boltzmann method for numerical simulations.
• Investigated a range of parameters: 0.05 ≤ swimming Re ≤ 2.0, 40 ≤ flow Re ≤ 160, and 0.2 ≤ κ ≤ 0.5.
• Validated simulation results against existing literature data.

Main Results:

• Identified four distinct motion modes: horizontal, attractive oscillation, oscillation, and chaotic.
• Increasing flow Reynolds number (Re) transitions motion from tumbling near the centerline to stable horizontal or oscillatory modes near the wall.
• Increasing swimming intensity promotes stable, periodic motion, while higher flow Reynolds numbers (Re) can induce spiral or rotational movement. Wall attraction (κ) is strengthened by increasing κ and modified by swimming intensity.

Conclusions:

• The study elucidates the complex interplay between particle propulsion, shear flow, and confinement.
• Parameter variations significantly alter squirmer dynamics, leading to diverse emergent behaviors.
• Findings provide insights into the fundamental physics governing micro-scale active matter in complex flows.