Steady flow in abdominal aortic aneurysm models has been examined for
four aneurysm sizes over Reynolds numbers from 500 to 2600. The Reynol
ds number is based on entrance tube diameter, and the inlet condition
is fully developed flow. Experimental and numerical methods have been
used to determine: (i) the overall features of the flow, (ii) the stre
sses on the aneurysm walls in laminar flow, and (iii) the onset and ch
aracteristics of turbulent flow. The laminar flow field is characteriz
ed by a jet of fluid (passing directly through the aneurysm) surrounde
d by a recirculating vortex. The wall shear stress magnitude in the re
circulation zone is about ten times less than in the entrance tube. Bo
th wall shear stress and wall normal stress profiles exhibit large mag
nitude peaks near the reattachment point at the distal end of the aneu
rysm. The onset of turbulence in the model is intermittent for 2000 <
Re < 2500. The results demonstrate that a slug of turbulence in the en
trance tube grows much more rapidly in the aneurysm than in a correspo
nding length of uniform cross section pipe. When turbulence is present
in the aneurysm the recirculation zone breaks down and the wall shear
stress returns to a magnitude comparable to that in the entrance tube
.