Affiliations: DITS-Fluid Mechabnics Laboratory, University
'La Sapienza' of Rome, Via Eudossiana 18-00184, Italy.
E-mail: stefania.espa@uniroma1.it
Abstract: One of the main consequences of chaos is that transport is enhanced
with respect to the fluid at rest, where only molecular diffusion is present.
Considering long times and spatial scales much larger than the length scale of
the velocity field, particles typically diffuse with a diffusion constant,
usually much bigger than the molecular one. Nevertheless there are some
important physical systems in which the particle motion is not a normal
diffusive process: in such a case one speaks of anomalous diffusion. In this
paper, anomalous diffusion is experimentally studied in an oscillating
two-dimensional vortex system. In particular, scalar enhanced diffusion due to
the synchronization between different characteristic frequencies of the
investigated flow (i.e., resonance) is investigated. The flow has been
generated by applying an electromagnetic forcing on a thin layer of an
electrolyte solution and measurements are made through image analysis. In
particular, by using the Feature Tracking (FT) technique, we are able to obtain
a large amount of Lagrangian data (i.e., the seeding density can be very high
and trajectories can be followed for large time intervals) and transport can be
characterized by analyzing the growth of the variance of particle displacements
versus time and the dependence of the diffusion coefficient on the flow
characteristic frequencies.