  In this work several lagrangian methods were used to analyze the mixing
processes in an experimental model of a constricted artery under a pulsatile
flow. Upstream Reynolds number $Re$ was changed between 1187 and 1999, while
the pulsatile period $T$ was kept fixed at 0.96s. Velocity fields were acquired
using Digital Particle Image Velocimetry (DPIV) for a region of interest (ROI)
located downstream of the constriction. The flow is composed of a central jet
and a recirculation region near the wall where vortex forms and sheds. To study
the mixing processes, finite time Lyapunov exponents (FTLE) fields and
concentration maps were computed. Two lagrangian coherent structures (LCS)
responsible for mixing and transporting fluid were found from FTLE ridges. A
first LCS delimits the trailing edge of the vortex, separating the flow that
enters the ROI between successive periods. A second LCS delimits the leading
edge of the vortex. This LCS concentrates the highest particle agglomeration,
as verified by the concentration maps. Moreover, from the particle residence
time maps (RT) the probability for a fluid particle of leaving the ROI before
one cycle was measured. As $Re$ increases, the probability of leaving the ROI
increases from 0.6 to 0.95. Final position maps $r{_f}$ were introduced to
evaluate the flow mixing between different subregions of the ROI. These maps
allowed us to compute an exchange index between subregions,
$\bar{\mathrm{EI}}$, which shows the main region responsible for the mixing
increase with $Re$. Finally by integrating the results of the different
lagrangian methods (FTLE, Concentration maps, RT and $r_f$ maps), a
comprehensive description of the mixing and transport of the flow was provided.
