Microscopic flow around a diffusing particle.

Area of Science:

• Fluid dynamics
• Computational physics
• Statistical mechanics

Background:

• Classical hydrodynamics describes fluid flow around objects using continuum assumptions.
• Stokes flow with slip boundary conditions is often used for small particles in fluids.
• Particle fluctuations can significantly alter microscopic fluid behavior.

Purpose of the Study:

• To compute the microscopic fluid flow induced by a tagged particle's motion using molecular dynamics simulations.
• To investigate deviations from classical hydrodynamics at the particle-fluid interface.
• To explore the impact of particle fluctuations on fluid properties and boundary conditions.

Main Methods:

• Molecular dynamics simulations of a tagged particle in a fluid.
• Analysis of fluid velocity fields at the microscopic level.
• Comparison with theoretical models like Stokes flow and experimental data from granular gases.

Main Results:

• Stokes solution with slip boundary conditions is recovered at distances beyond a few particle diameters.
• Particle fluctuations renormalize bath viscosity and lead to apparent violation of non-penetrability in the lab frame.
• A generalized boundary condition is identified, satisfied in the particle frame or for heavy particles.

Conclusions:

• Microscopic fluid flow is significantly influenced by particle dynamics and fluctuations.
• Classical hydrodynamic descriptions require modification to account for these effects.
• The findings have implications for understanding transport phenomena in complex fluids and granular systems.