Hydrodynamic interactions between a point force and a slender filament

Ivan Tanasijević; Eric Lauga

doi:10.1103/physrevfluids.6.124101

Hydrodynamic interactions between aerosol particles in the transition regime

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.632 ◽

2018 ◽

Vol 855 ◽

pp. 535-553 ◽

Cited By ~ 1

Author(s):

James Corson ◽

G. W. Mulholland ◽

M. R. Zachariah

Keyword(s):

Knudsen Number ◽

High Volume ◽

Mean Free Path ◽

Point Force ◽

Dynamics Simulation ◽

Hydrodynamic Interactions ◽

Transition Regime ◽

Brownian Dynamics Simulation ◽

Knudsen Numbers ◽

Continuum Flow

We present a method for calculating the hydrodynamic interactions between particles in the kinetic (or transition regime), characterized by non-negligible particle Knudsen numbers. Such particles are often present in aerosol systems. The method is based on our extended Kirkwood–Riseman theory (Corson et al., Phys. Rev. E, vol. 95 (1), 2017c, 013103), which accounts for interactions between spheres using the velocity field around a translating sphere as a function of Knudsen number. Results for the two-sphere problem at small Knudsen numbers are in good agreement with those obtained using Felderhof’s interaction actions for mixed slip-stick boundary conditions, which are accurate to order $r^{-7}$ (Felderhof, Physica A, vol. 89 (2), 1977, pp. 373–384). The strength of the interactions decreases with increasing Knudsen number. Results for two fractal aggregates demonstrate that one can apply a point force approach for interactions between particles in the transition regime; the interaction tensor is similar to the Oseen tensor for continuum flow. Using this point force approach, we present an analysis for the settling of an unbounded cloud of particles. Our analysis shows that for sufficiently high volume fractions and cloud radii, the cloud behaves as a gas droplet in continuum flow even when the individual particles are small relative to the mean free path of the gas. The method presented here can be applied in a Brownian dynamics simulation analogous to Stokesian dynamics to study the behaviour of a dense aerosol system.

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Hydrodynamics can determine the optimal route for microswimmer navigation

Communications Physics ◽

10.1038/s42005-021-00522-6 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Abdallah Daddi-Moussa-Ider ◽

Hartmut Löwen ◽

Benno Liebchen

Keyword(s):

Flow Field ◽

Hydrodynamic Interactions ◽

Optimal Trajectories ◽

Optimal Route ◽

Active Particles ◽

Navigation Strategy ◽

Navigation Strategies

AbstractAs compared to the well explored problem of how to steer a macroscopic agent, like an airplane or a moon lander, to optimally reach a target, optimal navigation strategies for microswimmers experiencing hydrodynamic interactions with walls and obstacles are far-less understood. Here, we systematically explore this problem and show that the characteristic microswimmer-flow-field crucially influences the navigation strategy required to reach a target in the fastest way. The resulting optimal trajectories can have remarkable and non-intuitive shapes, which qualitatively differ from those of dry active particles or motile macroagents. Our results provide insights into the role of hydrodynamics and fluctuations on optimal navigation at the microscale, and suggest that microorganisms might have survival advantages when strategically controlling their distance to remote walls.

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