Chaotic tracer scattering and fractal basin boundaries in a blinking vortex-sink system

We consider passive tracer advection in a model of a large planar basin of fluid with two sinks opened alternately. In spite of the incompressibility of the fluid, the phase space of the tracer dynamics contains (simple) attractors, the sinks. We show that the advection is chaotic due to the appearance of a locally Hamiltonian chaotic saddle. Properties of this saddle and its invariant manifolds are investigated, and fractal and dynamical characteristics of the tracer patterns are extracted by means of the thermodynamical formalism applied to the time-delay function.