Journal of Ultrasound in Medicine, Vol 15, Issue 10 679-688, Copyright © 1996 by American Institute of Ultrasound in Medicine
Steady flow in models of abdominal aortic aneurysms. Part I: Investigation of the velocity patterns
R. A. Peattie, C. L. Asbury, E. I. Bluth and J. W. Ruberti
Department of Biomedical Engineering, Tulane University, New Orleans, Louisiana 70118, USA.
As an investigation into the mechanical factors that lead to rupture of
abdominal aortic aneurysms, both color Doppler flow imaging and laser
Doppler velocimetry measurements of steady flow through a series of
aneurysm models are presented. The flow pattern in each model consisted of
a core of relatively fast-moving fluid traveling through the center of the
dilation, surrounded by an outer annulus of slowly recirculating fluid. At
flow rates below a Reynolds number of 1750 +/- 150, the flow was smooth,
steady, and laminar. At higher flow rates (Reynolds number above 2250 +/-
250), the flow was always irregular and turbulent. Between these fully
laminar and fully turbulent regimes the flow was intermittently turbulent.
Larger models showed a tendency to become turbulent at lower Reynolds
numbers than smaller models. In addition, turbulence was amplified in the
distal half of the model dilation, with the largest models producing
velocity fluctuations as great as 35% of the time-average centerline
velocities. These data suggest that larger aneurysms in vivo may be subject
to more frequent and intense turbulence than smaller aneurysms.
Concomitantly, increased turbulence may contribute significantly to risk of
rupture, as is discussed in Part II.
