Fluid Structure Interaction and Non-Newtonian Blood Flow in Stent Grafts for Abdominal Aortic Aneurysms

Abstract

Abdominal aortic aneurysm(AAA) is a common problem encountered which leads to dilation of the abdominal aorta. One novel way of treating AAA is using endovascular aortic repair (EVAR) where a polymer stent graft (SG) is used to redirect blood flow. Post operative concerns are common with EVAR like stent graft migration that are caused due to displacement forces acting on the ends of the SG. In this thesis, the aim is to correlate experimental results with a developed computational model which is used to evaluate forces acting on the ends of an iliac limb stent graft. Chosen liquid for the experiment was water as pressure is said to be the main driving force and viscous effects are negligible. Displacement forces are numerically evaluated using a finite volume approach for fluid-structure interaction (FSI) with the open source tool OpenFOAM for different pressures (145/80, 170/90, 195/100 mm.Hg) and different stroke rates (60, 80 and 100 BPM). Further, different blood viscosity models are studied and a comparison of forces for Newtonian and non-Newtonian blood models are presented. Wall shear stress(WSS) and velocity contours are presented for both blood models and complex flow phenomenon like secondary flow structures are explained. Viscous forces are found to be negligible and pressure is the main cause of displacement forces which is consistent with the experiment and justifies the usage of water in the experiment. Newtonian and non- Newtonian models yielded similar results for displacement forces as that of water and small variations were observed in velocities and WSS.