Topological transition and helicity conversion of vortex knots and links

Weiyu Shen, Jie Yao, Fazle Hussain, Yue Yang

Research output: Contribution to journalArticlepeer-review

Abstract

Topological transition and helicity conversion of vortex torus knots and links are studied using direct numerical simulations of the incompressible Navier-Stokes equations. We find three topological transitional routes (viz. merging, reconnection and transition to turbulence) in the evolution of vortex knots and links over a range of torus aspect ratios and winding numbers. The topological transition depends not only on the initial topology but also on the initial geometry of knots/links. For small torus aspect ratios, the initially knotted or linked vortex tube rapidly merges into a vortex ring with a complete helicity conversion from the writhe and link components to the twist. For large torus aspect ratios, the vortex knot or link is untied into upper and lower coiled loops via the first vortex reconnection, with a helicity fluctuation including loss of writhe and link, and generation of twist. Then, the relatively unstable lower loop can undergo a secondary reconnection to split into multiple small vortices with a similar helicity fluctuation. Surprisingly, for moderate torus aspect ratios, the incomplete reconnection of tangled vortex loops together with strong vortex interactions triggers transition to turbulence, in which the topological helicity decomposition fails due to the breakdown of vortex core lines.

Original languageEnglish (US)
Article numberA41
JournalJournal of Fluid Mechanics
Volume943
DOIs
StatePublished - Jul 25 2022

Keywords

  • topological fluid dynamics
  • vortex dynamics

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering
  • Applied Mathematics

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