Numerical simulation of blood flow in flexible carotid artery bifurcation

Abstract

To investigate the effect of the flexible artery wall on the flow field and to determine the wall shear stresses in the carotid artery wall, numerical simulations for the blood flow are carried out. For solving the equation of motion for the structure in typical fluid-structure interaction (FSI) problems, it is necessary to calculate the fluid force on the surface of the structure explicitly. To avoid the complexity due to the necessity of additional mechanical constraints, we use the combined formulation which includes both the fluid and structure equations of motion into single coupled variational equation. The Navier-Stokes equations for fluid flow are solved using a P2P1 Galerkin finite element method (FEM) and mesh movement is achieved using arbitrary Lagrangian-Eulerian (ALE) formulation. The Newmark method is employed for solving the dynamic equilibrium equations for linear elastic solid mechanics. The time-dependent, three-dimensional, incompressible flows of Newtonian fluids constrained in the flexible wall are analyzed. The study shows strongly skewed axial velocity and flow separation in the internal carotid artery (ICA). Flow separation results in locally low wall shear stress. High oscillatory shear and residence time exist near the carotid sinus which means high risk of atherogenesis. In particular, strong secondary motion and severe distortion of axial velocity profile at the upstream region of the sinus is generated in the large ICA angle case because of the geometric effect. Small ICA angle increases the area of particularly high oscillatory shear near the apex. On the other hand, the bifurcation angle has only a small effect on the possible risk of atherogenesis. Thus, relatively high ICA angle dependence of the atherogenesis risk region in observed. Further, the influence of the vessel wall thickness and wall stiffness in carotid artery to the flow field is investigated. A high correlation between vessel wall flexibility and vessel wall displacement is observed. Whereas, relatively slight dependence of vessel wall thickness and wall stiffness to the risk region of atherogenesis is observed.