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Vorticity Determines the Force on Bodies Immersed in Active Fluids
Thomas Speck1, Ashreya Jayaram1
1Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7-9, 55128 Mainz, Germany.
Physical Review Letters
|April 16, 2021
Summary
Passive bodies in active Brownian particle fluids move linearly or angularly based on shape. Forces driving this motion are linked to particle density and current far from the body, enabling rational design of self-propelling shapes.
Area of Science:
- Physics
- Soft Matter Physics
- Fluid Dynamics
Background:
- Active Brownian particles (ABPs) create dynamic fluid environments.
- Passive bodies in ABP fluids can exhibit directed motion.
- The forces governing this motion are not fully understood.
Purpose of the Study:
- To relate forces on passive bodies to far-field particle behavior.
- To investigate shape-dependent motion in ABP fluids.
- To understand the role of vorticity in particle propulsion.
Main Methods:
- Exploitation of the divergence theorem.
- Theoretical derivation of forces.
- Numerical corroboration of results.
- Analysis of particle density and current.
Main Results:
- Forces are composed of dipolar field contributions and boundary-induced vorticity.
- Vorticity is localized near the body and areas of changing curvature.
- Periodic systems exhibit different force scaling than unbounded systems.
Conclusions:
- The study provides a theoretical framework for understanding propulsion in ABP fluids.
- Rational design of particle shapes for controlled motion is enabled.
- Localized vorticity is key to propulsion and shape design.
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