Experimental study of the vortex rings generated by an oscillating disc
Résumé
This study experimentally investigates the generation of vortices at the edges of an
oscillating disc in an initially quiescent fluid. The roll-up of the shear layer produced at
the edge of the disc generates a vortex ring at each half-oscillation which interacts with the
vortex ring generated in the previous half-cycle.
First, we describe the different flow regimes by flow visualizations depending on the
disc diameter D, the amplitude A, and the frequency f of oscillation. We identify mainly
four regimes. The asymmetry between the vortex rings generated at each half-oscillation
characterizes one of these regimes: a circular core vortex ring is generated during one halfoscillation,
preventing the creation of the vortex ring that is supposed to be generated at
the next half-oscillation.
Then, in this asymmetric regime, we determine the features of the circular core vortex
ring by PIV (Particle Image Velocimetry). The characteristics of the vortex ring, i.e., its size,
position, and circulation, can be fitted to scaling laws depending on the variable parameters.