P.Nithiarasu and R.Löhner (Eds.) AXISYMMETRIC AND NON-AXISYMMETRIC FLOW AND WALL SHEAR STRESS IN A MODEL FUSIFORM ABDOMINAL AORTIC

Pulsatile flow through a sinusoidal bulge in an otherwise straight circular tube is used to model the fluid mechanics within a fusiform abdominal aortic aneurysm. Three-dimensional flow is computed using a high-order spectral-element/Fourier method, driven by an anatomically realistic heartbeat waveform. Model dimensions and parameters are chosen to describe human abdominal aortic aneurysms consid-ered both low and high risk in terms of their likelihood of rupture. A Reynolds number of 330, a Womersley number of 10.7, and aneurysm length and diameter ranges of 2.9-5.2 and 1.3-2.1 times the vessel diameter, respectively, are investigated. Variation in wall shear stress with both time and as a function of aneurysm dimension is computed. From computations on a bulge with maximum diameter approximately twice the undilated tube diameter, the flow is found to be naturally three-dimensional under conditions consistent with the human abdominal aorta. However, the dominant feature of the flow remains an axisymmetric vortex ring, which is generated at the proximal end of the bulge during systole. Both three-dimensional flow and non-uniformity in azimuthal wall-shear-stress distribution are most pronounced in the vicinity of the distal end of the bulge during the resting phase of the heartbeat. The axial distribution of wall shear stress scales approximately with the length of the bulge. The flow is sensitive to changes in the bulge diameter: a bulge with maximum diameter 1.9 times the vessel diameter invokes significantly more complex dynamics than a modest bulge of 1.3 diameters