Vortex dynamics within an idealized abdominal aortic aneurysm manifesting a stenosed angulated neck

Abdominal aortic aneurysm is a medical condition where the wall of the human aorta weakens as it dilates and can ultimately prove to be fatal. It is initially caused by pulsatile hemodynamic wall loading and is further aggravated by time-dependent displacement of flow structures within the aorta. The modified flow field increases the severity of wall loading, thus coupling the flow field with wall deformation. The details of the flow structures are strongly dependent on the three-dimensional flow space. The present study considers a symmetric aneurysm with an angulated stenosed neck on the inlet side and bent towards the left. On the outflow section, the bulged portion bifurcates into two branches. It is a variation of a simpler geometry, studied by the authors earlier. The spatio-temporal evolution of vortex structures in the three-dimensional geometry is studied at the flow frequency (f = 1.2 - 2.4 Hz) over a range of Reynolds numbers (Re_peak = 334 - 1192). Experiments have been conducted in a flow loop using particle image velocimetry and comparable 3D pulsatile flow simulations performed using the ANSYS-Fluent 22.1 software. With increasing Reynolds number, the vortex in the bulge shifts from one side of the wall to the other, aligning with the bend on the inflow section. The position of the vortex greatly impacts regions of low and high wall shear stress, weakening the arterial wall. Wall loading is significantly higher when the inflow geometry is bent while comparing it against a straight model. Inflow asymmetry also impacts flow distribution in the branches of the bifurcation.