Numerical Simulations of the Intra-Aneurysmal Vortex Shedding in Induced Mouse Abdominal Aortic Aneurysms Available to Purchase

A feature of particular interest observed in vivo in murine abdominal aortic aneurysm (AAA) is the presence of a vortex shed from the proximal edge of the abdominal aortic aneurysm. It is unclear whether the occurrence of the shed vortex is due to the periodic nature of the flow-rate waveform, to geometric features, or to the compliant nature of the vessel tissue. Numerical simulations were performed on 3D semi-idealized and 2D axi-symmetric models of the abdominal aortic aneurysm at a mean Reynolds number of 63 and a Womersley number of 2 (for unsteady inflow conditions). The numerical results from the 3D model showed good agreement with the flows visualized by Doppler Ultrasound with respect to the development of the observed shed vortex. The idealized axi-symmetric models under steady flow conditions showed no signs of vortex shedding. Under unsteady inflow conditions, however, shear-layer roll-up occurred near the peak systolic velocity. The presence of a proximal lip was found to lead to vortex separation (from the wall) earlier in the cardiac cycle, and the presence of the proximal narrowing led to the earliest vortex separation. The sensitivity to the inflow waveform shape also showed that the presence of the shedding, in the model with proximal narrowing, disappeared when the peak-to-mean velocity ratio was reduced by approximately half. Therefore, we conclude that the observed intra-aneurysmal vortex shedding is a shear-layer rollup phenomenon; however, the geometry can act to enhance further the observed vortex shedding.