Three-dimensional simulation of blood flow in an abdominal aortic aneurysm using steady and unsteady computational methods

Atherosclerosis and atherosclerotic aneurysms often occur in the abdominal aorta. Since blood flow can have a significant influence on the blood vessel walls and thrombus formation, steady and unsteady three-dimensional flow cases were simulated in an abdominal aortic aneurysm using a flow simulation package on a graphics workstation. In the steady flow case, three aneurysm models of 8.0 cm length were simulated using Reynolds numbers of 350 and 700 with a parabolic inlet flow profile. In the unsteady flow case, blood flow in an asymmetric aneurysm of 8.0 cm length was simulated at Reynolds numbers of 350 and 700 and 1400, and the inlet flow was a time-varying aortic wave form with a flat cross-sectional flow profile. In the steady flow case, in the aneurysm center, two symmetric vortices were formed, and flow separation started at the aneurysm inlet. Regions of high pressure were observed at the aneurysm exit caused by the symmetric jets that were formed, implying that this high-pressure region could be an area where rupture is most likely. The shear stress was low in the aneurysm portion of the vessel, and local maximum values were observed at the distal aneurysm constriction. In the unsteady flow case, the main vortex appeared and disappeared and changed position in the unsteady flow case and induced vortices were formed; in the steady flow case only one constant vortex was observed in the centerline view. Although the centerline view shows the vortices change position with time, cross-sectional view show that two symmetric vortices are present or partially formed throughout the entire flow cycle. Regions of maximum pressure moved depending on the flow cycle time; at peak flow, local pressure maximums were observed at the distal aneurysm; these oscillated, tending to put an additional strain on the distal portion of the aneurysm.