Ordering of small particles in one-dimensional coherent structures by time-periodic flows

TL;DR

This paper demonstrates that inertial particles in time-periodic flows tend to spontaneously form one-dimensional structures due to phase locking, explaining previously mysterious particle accumulation phenomena.

Contribution

It reveals a new mechanism linking inertial particle alignment to phase locking in time-periodic flows, explaining experimental particle accumulation structures.

Findings

Inertial particles form one-dimensional structures in certain flows.

Phase locking explains particle accumulation phenomena.

Small particles can deviate from flow trajectories, forming coherent structures.

Abstract

Small particles transported by a fluid medium do not necessarily have to follow the flow. We show that for a wide class of time-periodic incompressible flows inertial particles have a tendency to spontaneously align in one-dimensional dynamic coherent structures. This effect may take place for particles so small that often they would be expected to behave as passive tracers and be used in PIV measurement technique. We link the particle tendency to form one-dimensional structures to the nonlinear phenomenon of phase locking. We propose that this general mechanism is, in particular, responsible for the enigmatic formation of the `particle accumulation structures' discovered experimentally in thermocapillary flows more than a decade ago and unexplained until now.