Passive tracer transport in a four-vortex hydrodynamic system

Passive tracer transport processes in a four-vortex quasi-two-dimensional f low that are due to regular reconnections occurring between streamlines of the same sign after the stationary now loses its stability are studied expe rimentally. These processes are characterized by a relatively rapid mixing between vortices of the same vorticity sign and a slow mixing between regio ns differing in vorticity sign, which can be interpreted in the context of the theory of adiabatic chaos. Typical trajectories of Lagrangian particles are classified. The laboratory experimental data are compared to numerical results obtained by integrating trajectories of Lagrangian particles in th e flow field measured previously in detail. A qualitative agreement between experiment and theory is observed; however a strong discrepancy between th em is revealed. The randomization of particle trajectories in the laborator y experiment proceeds significantly more slowly, which testifies to traject ory ordering due to the small-scale structure of the flow field.