Demonstration of Experimental Three Dimensional Finite Time Lyapunov Exponents with Inertial Particles

TL;DR

This paper introduces an experimental method to measure three-dimensional finite time Lyapunov exponents for multiple particle groups in multiphase flows, enabling direct analysis of flow structures without intensive computation.

Contribution

It presents a novel experimental approach to directly compute finite time Lyapunov exponents for inertial particles in 3D flows from particle images.

Findings

Successfully measured 3D Lyapunov exponent fields in turbulence.

Identified Lagrangian coherent structures for inertial particles.

Demonstrated the method's applicability to multiphase flows.

Abstract

This work provides an experimental method for simultaneously measuring finite time Lyapunov exponent fields for multiple particle groups, including non-flow tracers, in three-dimensional multiphase flows. From sequences of particle images, e.g., from experimental fluid imaging techniques, we can directly compute the flow map and coherent structures, with out performing the computationally costly numerical integration. This is particularly useful to find three-dimensional Lagrangian coherent structures for inertial particles, that do not follow the bulk fluid velocity, as we demonstrate for a grid turbulence experiment. The technique described may provide a new means for exploring the physics of experimental multi-phase flows.