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Direct numerical simulations of a microswimmer in a viscoelastic fluid
Takuya Kobayashi1, Gerhard Jung1,2, Yuki Matsuoka3
1Department of Chemical Engineering, Kyoto University, Kyoto 615-8510, Japan. ryoichi@cheme.kyoto-u.ac.jp.
Soft Matter
|September 11, 2023
Summary
Fluid elasticity significantly impacts particle motion. Swirling flows enhance squirmer speed in viscoelastic fluids, with pushers outperforming pullers and specific viscosity ratios maximizing propulsion.
Area of Science:
- Fluid dynamics
- Rheology
- Biophysics
Background:
- Understanding micro-particle and micro-organism locomotion in complex fluids is crucial.
- Viscoelastic fluids exhibit unique flow behaviors not seen in Newtonian fluids.
Purpose of the Study:
- To investigate the motion of passive and active squirming particles in Newtonian and viscoelastic fluids using the smoothed profile method.
- To elucidate the role of fluid elasticity and particle-generated flow on swimming dynamics.
Main Methods:
- Direct numerical simulations utilizing the smoothed profile (SP) method.
- Analysis of particle velocity, fluid velocity fields, and polymer conformation.
- Investigation of forces on fixed squirmers to understand propulsion mechanisms.
Main Results:
- Fluid elasticity significantly alters particle transient behavior and steady-state velocity.
- Swirling flow enhances squirmer swimming speed with increasing Weissenberg number.
- Pushers outperform pullers in Oldroyd-B fluids; maximum speeds occur at intermediate viscosity ratios.
Conclusions:
- Swirling flow in viscoelastic fluids enhances propulsion through pusher-like extensional flow characteristics and asymmetric polymer conformation.
- Polymer stress is critical for enhanced swimming speeds of swirling squirmers.
- Particle type and fluid properties (elasticity, viscosity ratio) critically influence locomotion in complex fluids.
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