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Séminaire Christian JONSSON

22 mars 2012

The effect of ambient turbulence upon the propagation of a vortex ring

Christian JONSSON - Univ. College of London

Vendredi 23 mars à 15h30 - Amphithéâtre Nougaro

Abstract :

An experimental investigation was undertaken to study how turbulence in the ambient environment interacts with and modifies the dynamics of a vortex ring. In particular, focus was put on determining how the presence of external turbulence affects the scaling of the vortex ring propagation velocity and radius with time (i.e. how the ring slows down and grows). The turbulence was generated by towing a grid of bars through a stationary water tank, and the vortex ring by ejecting fluid impulsively through a nozzle into the tank. The vortex ring was marked with dye and its motion recorded by a camera ; an image processing code was developed to derive the position and structure of the ring as a function of time. It was found that a vortex ring penetrates a relatively short distance when injected into a turbulent
environment ; this distance decreases with the relative intensity of the ambient turbulence. Further, it was noted that the effect on the structure of the ring two-fold : the turbulence tended both to induce irregularity on the vortex core and to stretch the core.