Optimal transient growth on a vortex ring and its transition via cascade of ringlets

X. Mao, F. Hussain

Research output: Contribution to journalArticle

3 Scopus citations

Abstract

Linear and nonlinear transient growths of perturbations on a vortex ring up to Reynolds number ( circulation/viscosity) are studied. For short time intervals, perturbations around the ring axis undergo the strongest linear transient growth and lead to secondary structures in the form of ringlets, owing to the Orr mechanism and an inviscid vorticity-amplification mechanism: in contrast to the well-reported instabilities and lobe structures along the vortex ring core. These secondary ringlet structures induce a tertiary group of ringlets through similar transient perturbation growth. This cascade of ringlets lead to the breakup of the main ring even before activation of the vortex-core instabilities. Such a cascade scenario is also observed in the development of a vortex ring perturbed by random disturbance in the axis region. These new modes and mechanisms for the generation and breakup of vortex ring structures bring insights into the dynamics and control of vortex ring flows.

Original languageEnglish (US)
Pages (from-to)269-286
Number of pages18
JournalJournal of Fluid Mechanics
Volume832
DOIs
StatePublished - Dec 10 2017

Keywords

  • transition
  • vortex breakdown
  • vortex instability

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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