Extracting dominant dynamics about unsteady base flows

TL;DR

This paper reviews methods for extracting dominant flow dynamics and features in unsteady, aperiodic base flows, highlighting current techniques and future research directions in data-driven and operator-based approaches.

Contribution

It provides a comprehensive overview of existing methods for analyzing unsteady base flows and identifies key areas for future research in the field.

Findings

Reviewed data-driven decomposition techniques

Discussed operator-based methods and causality analysis

Highlighted future research directions

Abstract

A wide range of techniques exist for extracting the dominant flow dynamics and features about steady, or periodic base flows. However, there have been limited efforts in extracting the dominant dynamics about unsteady, aperiodic base flow. These flows appear in many applications such as when there is a sudden change in the flow rate through a pipe, when an airfoil experiences stall, or when a vortex forms. For these unsteady flows, it is valuable to know not only the dynamics of the base flow but also the features that form around this base flow. Here, we discuss the current state of research on extracting important flow structures and their dynamics in such cases with time-varying base flows. In particular, we consider data-driven decompositions, operator-based methods, causality analysis, and some other approaches. We also offer an outlook and call attention to key areas that require future efforts.