Lagrangian coherent structures and inertial particle dynamics

TL;DR

This paper explores how inertial particles behave in fluid flows by analyzing finite-time Lyapunov exponents, revealing structures that influence particle clustering and dispersion, with implications for understanding particle transport in complex flows.

Contribution

It introduces a novel application of FTLE fields to characterize inertial particle dynamics and structures in unsteady flows, incorporating the effects of Stokes number and density ratio.

Findings

Heavier particles attract to negative-time FTLE ridges.

Lighter particles are repelled by these FTLE structures.

Stokes number influences the filtering of particle trajectories.

Abstract

In this work we investigate the dynamics of inertial particles using finite-time Lyapunov exponents (FTLE). In particular, we characterize the attractor and repeller structures underlying preferential concentration of inertial particles in terms of FTLE fields of the underlying carrier fluid. Inertial particles that are heavier than the ambient fluid (aerosols) attract onto ridges of the negative-time fluid FTLE. This negative-time FTLE ridge becomes a repeller for particles that are lighter than the carrier fluid (bubbles). We also examine the inertial FTLE (iFTLE) determined by the trajectories of inertial particles evolved using the Maxey-Riley equations with non-zero Stokes number and density ratio. Finally, we explore the low-pass filtering effect of Stokes number. These ideas are demonstrated on two-dimensional numerical simulations of the unsteady double gyre flow.