Visualization of Lagrangian fluid transport of a vortex ring based on time-resolved PIV

We carry out experiments on vortex ring flows submerged underwater which are generated by a pulsatile circular jet with the stroke ratio of 10. The pulsatile Reynolds number, based on centerline exit velocity and jet diameter, is a cosinusoidal function of time with a mean part of 2000 and an oscillating part of 820. This axisymmetric flow field is measured in a meridian symmetry plane by time-resolved planar particle image velocimetry. For revealing the interaction among the starting vortex ring, the trailing jet and the ambient quiescent fluid, we apply finite-time Lyapunov exponent in the Lagrangian framework to the Eulerian-based PIV dataset. By tracking trajectories of typical virtually color-dyed fluid parcels, we obtain clear visualizations of the entrainment and detrainment processes by the vortex ring, the advection transport of the trailing jet and the advection transport of trailing shear layer, during the longitudinal propagation of the vortex ring.