Influence of Abdominal Aortic Aneurysm Shape on Hemodynamics

Direct numerical simulation was performed on two patient-specific abdominal aortic aneurysms (AAA) using physiologically realistic flow conditions. The patients have AAA with diameters of approximately 5 and 7 cm, respectively. The blood flow hemodynamics are shown to consist of large-scale periodic structures and the flow transitions from laminar-to-turbulent and back to laminar during a pulse. Transition does not occur until after the maximum flow rate has been reached and turbulence persists in the AAA after the bulk flow decelerates to a laminar condition. For both cases, a jet of blood forms at the AAA throat and impinges against the arterial wall at the site of maximal aortic diameter. During the pulse structures shear across the AAA causing locally high wall shear stress (WSS). It is shown that the cases have significantly different hemodynamics. The smaller sized AAA has faster moving flow structures, higher WSS, higher turbulent kinetic energy, and the blood spirals down the AAA toward the iliac arteries. In the larger sized AAA, the blood flow channels down on the anterior side and a large recirculation zone forms on the posterior side. A large recirculation zone causes low WSS which is know to promote atherosclerosis.