On the identification of a vortex

Jinhee JEong, Fazle Hussain

Research output: Contribution to journalArticle

4201 Scopus citations

Abstract

Considerable confusion surrounds the longstanding question of what constitutes a vortex, especially in a turbulent flow. This question, frequently misunderstood as academic, has recently acquired particular significance since coherent structures (CS) in turbulent flows are now commonly regarded as vortices. An objective definition of a vortex should permit the use of vortex dynamics concepts to educe CS, to explain formation and evolutionary dynamics of CS, to explore the role of CS in turbulence phenomena, and to develop viable turbulence models and control strategies for turbulence phenomena. We propose a definition of a vortex in an incompressible flow in terms of the eigenvalues of the symmetric tensor S2+122; here S and Q are respectively the symmetric and antisymmetric parts of the velocity gradient tensor ∇u. This definition captures the pressure minimum in a plane perpendicular to the vortex axis at high Reynolds numbers, and also accurately defines vortex cores at low Reynolds numbers, unlike a pressure-minimum criterion. We compare our definition with prior schemes/definitions using exact and numerical solutions of the Euler and Navier-Stokes equations for a variety of laminar and turbulent flows. In contrast to definitions based on the positive second invariant of ∇u or the complex eigenvalues of ∇u. our definition accurately identifies the vortex core in flows where the vortex geometry is intuitively clear.

Original languageEnglish
Pages (from-to)69-94
Number of pages26
JournalJournal of Fluid Mechanics
Volume285
DOIs
StatePublished - Feb 1995

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