Abstract
We report on an experimental study of turbulent vortex rings injected with velocity U v0 into a grid-generated turbulent flow (with RMS streamwise velocity u *) and followed relative to the mean flow. The initial Reynolds number of the vortices varies from 4500 to 11,500. The turbulence was characterised by an intensity It =u */U v0, which varied over the range 0<It <0.03. A mathematical model based on a stochastic model of the vortex core is developed to explain and interpret the results. The vortex radius grows diffusively in time with the rate of increase of the square of the vortex radius increasing linearly with It . As the vortices grow, they slow down sufficiently rapidly in a manner that they penetrate a finite distance into the turbulence. The vortex velocity, averaged over many experiments, showed an initial t −1 decay, consistent with Maxworthy’s experiments. The analysis and experiments show that such vortices ultimately only move a finite distance from their point of generation and this distance varies inversely with It .
Acknowledgments
Acknowledgements
OA is indebted to Prof. Dr. Eduard Naudascher (University of Karlsruhe). CAK acknowledges support from ASTAR.