  We investigate the dynamics of passive particles in a two-dimensional
incompressible open flow composed of a fixed topographical point vortex and a
background current with a periodic component. The tracer dynamics is found to
be typically chaotic in a mixing region and regular in far upstream and
downstream regions of the flow. Chaotic advection of tracers is proven to be of
a homoclinic nature with transversal intersections of stable and unstable
manifolds of the saddle point. In spite of simplicity of the flow, chaotic
trajectories are very complicated alternatively sticking nearby boundaries of
the vortex core and islands of regular motion and wandering in the mixing
region. The boundaries act as dynamical traps for advected particles with a
broad distribution of trapping times. This implies the appearance of
fractal-like scattering function: dependence of the trapping time on initial
positions of the tracers. It is confirmed numerically by computing a trapping
map and trapping time distribution which is found to be initially Poissonian
with a crossover to a power law at the PDF tail. The mechanism of generating
the fractal is shown to resemble that of the Cantor set with the Hausdorff
fractal dimension of the scattering function to be equal to d ~= 1.84.
