Capturing multiscale interactions in fluid flow via Lagrangian coherent structures and modal analysis
Phys. Rev. Fluids 11, 094902 – Published 11 September, 2026
DOI: https://doi.org/10.1103/kgw4-ywtm
Abstract
We consider the relationship between Eulerian modal decompositions and Lagrangian coherent structures. The model sensitivity framework developed by Kaszás and Haller [Chaos 30, 113144 (2020)] is used to express data-driven modal representations of fluid flow in a Lagrangian space. The method, based on the computation of the finite-time Lyapunov exponent, computes the amplitude perturbations experienced by fluid particles due to specific modal components of the flow. Demonstrations of the method are presented for both periodic and turbulent flows, including direct numerical simulation (DNS) data of the classical cylinder wake flow, experimental data from the wake past an oscillating foil, and DNS data of a turbulent channel flow. This method provides a way to understand how Eulerian mode structures interact dynamically with features of the Lagrangian coherent structure across scales, offering additional physical insight into modal decompositions.
