  An improved understanding of how vortices develop and propagate under
pulsatile flow can shed important light on the mixing and transport processes
including the transition to turbulent regime occurring in such systems. For
example, the characterization of pulsatile flows in obstructed artery models
serves to encourage research into flow-induced phenomena associated with
changes in morphology, blood viscosity, wall elasticity and flow rate. In this
work, an axisymmetric rigid model was used to study the behaviour of the flow
pattern with varying constriction degree ($d_0$), mean Reynolds number
($\bar{Re}$) and Womersley number ($\alpha$). Velocity fields were acquired
experimentally using Digital Particle Image Velocimetry and generated
numerically. For the acquisition of data, $\bar{Re}$ was varied from 385 to
2044, $d_0$ was 1.0 cm and 1.6 cm, and $\alpha$ was varied from 17 to 33 in the
experiments and from 24 to 50 in the numerical simulations. Results for the
considered Reynolds number, showed that the flow pattern consisted of two main
structures: a central jet around the tube axis and a recirculation zone
adjacent to the inner wall of the tube, where vortices shed. Using the
vorticity fields, the trajectory of vortices was tracked and their displacement
over their lifetime calculated. The analysis led to a scaling law equation for
the maximum vortex displacement as a function of a dimensionless variable
dependent on the system parameters Re and $\alpha$.
