Problems with identification of vortex rings when using anemometry measurements

Measurement of key vortex rings properties with the use of anemometry techniques is not so straightforward due to the angular dispersion of these structures and in consequence change of their trajectories as they move downstream. Owing to the fact that in available literature no much attention is paid to this issue, there is still a need to address this problem. In the present work we show some preliminary data which allowed to quantify the dispersion of vortex rings when these propagate over a distance up eight orifice diameters. The presented results indicate that the vortex structures generated at a certain frequency are characterized by increasing unrepeatability and angular dispersion as a function of distance from the generator. This leads to difficulties in their identification because their position in respect to the fixed position of the hot-wire probe changes.