Experimental study of transition to turbulence in steady flow through rigid models of abdominal aortic aneurysms

As an investigation into the mechanical factors which contribute to aneurysm growth and rupture, flow field measurements for steady flow are presented for a range of Reynolds numbers. Steady flow through rigid aneurysm models with roughly elliptical geometry is studied. Data is reported for a model of length 4d and diameter 2.5d, where d is the inner diameter of the entrance tube. Flow rates were chosen such that model Reynolds numbers matched in vivo Reynolds numbers for a range of subject activity level from resting to highly active. Laser-Doppler velocimetry (LDV) was used to verify flow patterns visualized with CDFI, and to quantify the flow velocities during laminar, transition and turbulent flow regimes. A well defined core flow was observed for all Reynolds numbers studied. The observed flow as laminar at Re=450 and Re=1300, and a stable recirculation zone occurred outside the core flow. Turbulent flow was observed at Re=2800 and no recirculation was seen in this case. This investigation represents an initial step in a more extensive study of flow fields within abdominal aortic aneurysms, the results of which will have significant implications for clinical decisions concerning the treatment of aortic aneurysms.