An investigation of the flow field within patient-specific models of an abdominal aortic aneurysm under steady inflow conditions

The flow fields within three patient-specific models of an abdominal aortic aneurysm (AAA) were investigated under steady laminar inflow conditions over a range of Reynolds numbers. Each model extended from the renal arteries to downstream of the iliac bifurcation. The aneurysms (referred to as models A, B, and C) are mature, with D/d ratios of 1.83, 1.57, and 1.95 respectively. The mass flowrates in each of the iliac arteries were equal. Using flow visualization it was observed that the flow proximally in the aneurysm was characterized by a primary jet that separated from either the posterior wall or the lateral wall or both, producing large recirculating zones. The primary jet impinged either normally or obliquely upon the anterior or right lateral wall in the distal half of the aneurysm, the flow distally in the aneurysm having been greatly disturbed. Measurements of the turbulence intensity along the median lumen centre-line showed that in each model the onset of transition and full turbulence occurred at Reynolds numbers much lower than those previously measured in idealized models. Computational fluid dynamics showed substantial differences in the velocity and stress fields when using the shear stress transport turbulence model as opposed to a laminar viscous model. It was also observed that turbulence was largely produced along the shear layers surrounding the primary jet and, in particular, at interfaces between the jet and the recirculating zones. In conclusion, turbulence may be expected to exist at Reynolds numbers typically encountered within an AAA, and it must be taken account of in an analysis of the flow field.