Cascade leading to the emergence of small structures in vortex ring collisions

Ryan McKeown, Rodolfo Ostilla-Mónico, Alain Pumir, Michael P. Brenner, Shmuel M. Rubinstein*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

When vortex rings collide head-on at high enough Reynolds numbers, they ultimately annihilate through a violent interaction which breaks down their cores into a turbulent cloud. We experimentally show that this very strong interaction, which leads to the production of fluid motion at very fine scales, uncovers direct evidence of an iterative cascade of instabilities in a bulk fluid. When the coherent vortex cores approach each other, they deform into tentlike structures and the mutual strain causes them to locally flatten into extremely thin vortex sheets. These sheets then break down into smaller secondary vortex filaments, which themselves rapidly flatten and break down into even smaller tertiary filaments. By performing numerical simulations of the full Navier-Stokes equations, we also resolve one iteration of this instability and highlight the subtle role that viscosity must play in the rupturing of a vortex sheet. The concurrence of this observed iterative cascade of instabilities over various scales with those of recent theoretical predictions could provide a mechanistic framework in which the evolution of turbulent flows can be examined in real time as a series of discrete dynamic instabilities.

Original languageAmerican English
Article number124702
JournalPhysical Review Fluids
Volume3
Issue number12
DOIs
StatePublished - Dec 2018
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2018 American Physical Society.

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