Stochastic dynamics of particles trapped in turbulent flows

TL;DR

This study investigates the long-term behavior of large particles in turbulent shear flows, revealing slow dynamics and trapping phenomena modeled effectively by stochastic equations with inhomogeneous fluctuations.

Contribution

It introduces a stochastic model capturing particle trapping and slow dynamics in turbulent flows, emphasizing the role of noise correlation and spatial inhomogeneity.

Findings

Particles exhibit slow back-and-forth motions between attractors.

A stochastic model with colored noise reproduces experimental dynamics.

Inhomogeneous fluctuations are essential for accurate modeling.

Abstract

The long time dynamics of large particles trapped in two inhomogeneous turbulent shear flows is studied experimentally. Both flows present a common feature, a shear region that separates two colliding circulations, but with different spatial symmetries and temporal behaviors. Because large particles are less and less sensitive to flow fluctuations as their size increases, we observe the emergence of a slow dynamics corresponding to back-and-forth motions between two attractors, and a super-slow regime synchronized with flow reversals when they exist. Such dynamics is substantially reproduced by a one dimensional stochastic model of an over-damped particle trapped in a two-well potential, forced by a colored noise. An extended model is also proposed that reproduces observed dynamics and trapping without potential barrier: the key ingredient is the ratio between the time scales of the noise correlation and the particle dynamics. A total agreement with experiments requires the introduction of spatially inhomogeneous fluctuations and a suited confinement strength.