TECHNICAL PAPERS: Fluids/Heat/Transport

Pulsatile Flow in Fusiform Models of Abdominal Aortic Aneurysms: Flow Fields, Velocity Patterns and Flow-Induced Wall Stresses

[+] Author and Article Information
Robert A. Peattie

Department of Chemical Engineering, 102 Gleeson Hall, Oregon State University, Corvallis, OR 97331 

Tiffany J. Riehle

Department of Pediatrics, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555  

Edward I. Bluth

Dept. of Radiology, Alton Ochsner Medical Foundation and Clinic, 514 Jefferson Hwy., New Orleans, LA 70121

J Biomech Eng 126(4), 438-446 (Sep 27, 2004) (9 pages) doi:10.1115/1.1784478 History: Received October 22, 2003; Revised April 02, 2004; Online September 27, 2004
Copyright © 2004 by ASME
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Schematic diagram of the aneurysm models. Critical dimensions d,D and L along with the positions of pressure taps are shown in the lower images.
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(a) Diagram of the flow loop, showing the positions of the model, the reservoirs and the control valves. Flow in the forward direction refers to proximal-to-distal motion from the forward reservoir, while retrograde motion is the reverse. (b) Triphasic pulsatile flow waveform used in the experiments, based on measurements in human subjects. This waveform consists of a large systolic forward flow pulse, followed by a period of net retrograde flow, then a slower flow diastole.
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Velocity profiles in (a) model 2 (D/d=1.88, simulates a 4.3 cm AAA) and (b) model 5 (D/d=2.75, simulates a 6.3 cm AAA) at six phases of the flow cycle: (i) flow acceleration, t/T=0.035; (ii) peak systole, t/T=0.16; (iii) flow deceleration, t/T=0.35; (iv) peak retrograde flow, t/T=0.55; (v) early diastole, t/T=0.77; (vi) late diastole, t/T=0.87. The radial and axial coordinates, r and x, are normalized by the radius of the nondilated entrance tube, R. A reference arrow in each panel shows the velocity scale, while a waveform icon indicates the phase.
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Qualitative streamline sketches, at the same phases of the flow cycle as Fig. 3: (a) applies to flow acceleration and systole, t/T=0.035 and t/T=0.16; (b) flow deceleration, t/T=0.35; (c) peak retrograde flow, t/T=0.55; (d) and (e) diastole, t/T=0.77 and 0.87. The streamlines illustrate the appearance and evolution of vortices in the flow.
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Wall pressure distribution along model 4 (D/d=2.56, simulates a 5.9 cm AAA) at three phases of the flow cycle, t/T=0.12, 0.88 and 0.33, corresponding to systole, flow deceleration and diastole, respectively. At each phase, although the pressure was nearly constant along the bulge, it decreased along the proximal section of the wall then increased along the distal section.
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(a) Wall shear stress distribution along model 4 at four flow phases. In every model, the maximum shear stress occurred at the distal end of the bulge, at peak systole. (b) Dependence of the maximum systolic wall shear stress on bulge diameter. There is a strong peak at D/d=1.88.
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Instability intensity measured along the centerline of five models. A sharp increase in intensity occurred in the distal half of each model. Except for model 2, larger models showed a greater increase in intensity than smaller models. In addition, the position of maximum intensity migrated distally as the bulge diameter increased.




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