STEADY FLOW IN ABDOMINAL AORTIC-ANEURYSM MODELS

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 .