Automated Vortex Analysis through Axis-line Extraction: Application in Newtonian and Viscoelastic Turbulence

Abstract: Coherent structures such as vortices are central to understanding the self-sustaining dynamics of flow turbulence. Various vortex identification methods have been proposed in the past for converting detailed velocity fields into scalar fields representing local vortex strength. The analysis of such vortex fields still relies heavily on visual inspection and intuitive arguments. We propose an algorithm, Vortex Axis Tracking by Iterative Propagation (VATIP), to extract the axis-lines of vortices that represent their configurations. Axis-lines are used to identify individual vortices from a continuous flow field, as well as to quantify the size, position, shape, and topology of vortices in a fully automated process without human intervention. Application to viscoelastic channel flow data reveals a distinct shift in vortex regeneration mechanisms that underpins the transition between low- and high-extent drag reduction (LDR and HDR) stages. In our ongoing efforts, statistical classification is applied to vortex axis-lines to study the effects of different types of vortices in turbulent dynamics. Temporal tracking of axis-lines between time instances further depicts the lifetime evolution and regeneration dynamics of vortices. Our ultimate goal is to develop a fully automated, objective, and quantitative toolset for studying turbulent vortex dynamics.

Bio: Dr. Li Xi is an Associate Professor of Chemical Engineering at McMaster University in Hamilton, Ontario, Canada. He earned his Ph.D. from the University of Wisconsin–Madison, where he studied the nonlinear dynamics and flow instabilities of viscoelastic fluids. He subsequently conducted postdoctoral research at the Massachusetts Institute of Technology (MIT), focusing on polymer materials modeling and its applications in pharmaceutical manufacturing. At McMaster, Dr. Xi leads a multidisciplinary research group working at the intersection of fluid mechanics, polymer dynamics and rheology, and advanced manufacturing. His work in fluid mechanics centers on wall‑bounded turbulence and turbulent drag reduction by polymer additives, using direct numerical simulation as a primary investigative tool. More recently, his group has advanced turbulent vortex analysis by developing Vortex Axis Tracking by Iterative Propagation (VATIP), a methodology that identifies the rotation axes of all vortices in a turbulent flow field. This framework aims to establish a toolkit for high‑throughput, quantitative, and objective studies of vortex dynamics in turbulence.