Lagrangian coherent structures in the human carotid artery bifurcation

The carotid artery bifurcation is known as a site of atheromatous plaque formation which is closely related to hemodynamics. To investigate the fluid mechanics inside the bifurcation, a transparent model of the carotid geometry was built to estimate the feasibility of using stereoscopic particle image velocimetry (PIV) in a complex three-dimensional geometry. As a first approach, steady inflow conditions are considered. Velocity data are acquired in cross-sectional planes and combined to yield the full three-dimensional velocity vector field in the region of the bifurcation. The finite-time Lyapunov exponent (FTLE) is used as a criterion to reveal the complex flow structure and is found to be particularly efficient in discriminating between reverse flow and recirculation regions. The Lagrangian criterion is also computed with time-resolved, two-component PIV measurements obtained by increasing the Reynolds number up to the onset of unsteadiness. The FTLE field produces in this case a detailed visualization of the instability development.