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Research Papers

CFD and PTV Steady Flow Investigation in an Anatomically Accurate Abdominal Aortic Aneurysm

[+] Author and Article Information
Evangelos Boutsianis, Ufuk Olgac

Laboratory of Thermodynamics in Emerging Technologies, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland

Michele Guala, Klaus Hoyer

Institute of Environmental Engineering, ETH Zurich, 8092 Zurich, Switzerland

Simon Wildermuth

Institute of Diagnostic Radiology, University Hospital of Zurich, Raemistrasse 100, 8091 Zurich, Switzerland

Yiannis Ventikos

Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK

Dimos Poulikakos1

Laboratory of Thermodynamics in Emerging Technologies, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerlanddimos.poulikakos@ethz.ch

Somatom Volume Zoom, Siemens Medical Solution, Erlangen, Germany.

CARE Bolus System, Siemens Medical Solution, Forchheim, Germany.

Visipaque 320, Amersham Health, Buckinghamshire, United Kingdom.

Mercury Computer Systems Inc., Duesseldorf, Germany.

Elastrat Sàrl, Geneva, Switzerland.

Eclipse, Bellingham & Stanley Ltd.

KROHNE Altometer IFC 080, KROHNE Messtechnik GmbH & Co. KG, Duisburg, Germany.

The Dow Chemical Company, http://www.dow.com/glycerine/resources/table18.htm.

Fastcam-ultima APX.

Nikkor.

HTI 400, Osram.

Fluent Inc., Darmstadt, Germany.

ESI Group CFD, Paris, France.

Laboratory of Thermodynamics in Emerging Technologies, ETH Zurich.

Institute of Environmental Engineering, ETH Zurich.

Institute of Diagnostic Radiology, University Hospital of Zurich.

1

Corresponding author.

J Biomech Eng 131(1), 011008 (Nov 21, 2008) (15 pages) doi:10.1115/1.3002886 History: Received July 18, 2007; Revised June 27, 2008; Published November 21, 2008

There is considerable interest in computational and experimental flow investigations within abdominal aortic aneurysms (AAAs). This task stipulates advanced grid generation techniques and cross-validation because of the anatomical complexity. The purpose of this study is to examine the feasibility of velocity measurements by particle tracking velocimetry (PTV) in realistic AAA models. Computed tomography and rapid prototyping were combined to digitize and construct a silicone replica of a patient-specific AAA. Three-dimensional velocity measurements were acquired using PTV under steady averaged resting boundary conditions. Computational fluid dynamics (CFD) simulations were subsequently carried out with identical boundary conditions. The computational grid was created by splitting the luminal volume into manifold and nonmanifold subsections. They were filled with tetrahedral and hexahedral elements, respectively. Grid independency was tested on three successively refined meshes. Velocity differences of about 1% in all three directions existed mainly within the AAA sack. Pressure revealed similar variations, with the sparser mesh predicting larger values. PTV velocity measurements were taken along the abdominal aorta and showed good agreement with the numerical data. The results within the aneurysm neck and sack showed average velocity variations of about 5% of the mean inlet velocity. The corresponding average differences increased for all velocity components downstream the iliac bifurcation to as much as 15%. The two domains differed slightly due to flow-induced forces acting on the silicone model. Velocity quantification through narrow branches was problematic due to decreased signal to noise ratio at the larger local velocities. Computational wall pressure and shear fields are also presented. The agreement between CFD simulations and the PTV experimental data was confirmed by three-dimensional velocity comparisons at several locations within the investigated AAA anatomy indicating the feasibility of this approach.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 3

Panel (a): Overview of the generated luminal surface mesh showing the division into manifold and nonmanifold domains. Panel (b): Definition of the main gridding parameters Ri on the inlet. Panel (c): Close-up of the surface grid in the vicinity of the visceral branches.

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Figure 4

Perspective, panel (a), and planar, panel (b), views of the cross section and the polyline utilized in the grid independency study

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Figure 5

Contour plot comparisons of velocity components, panels (a)–(c), and pressure, panel (d), along the planar cross section indicated in Fig. 4

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Figure 12

Velocity streamlines within the AAA model colored with the velocity magnitude

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Figure 1

Overview of the experimental setup. Panel (a): Photograph of the AAA model tank. The terminal branches are labeled as (1) supraceliac aorta, (2) celiac trunk, (3) superior mesenteric, (4) left renal, (5) right renal, (6) left external iliac, (7) right external iliac, (8) left internal iliac, and (9) right internal iliac. Panel (b): Schematic of the experimental setup with indicated parts: (1) reservoir, (2) volumetric pump, (3) bypass-able filter, (4) electromagnetic flow meter, (5) inflow conditioner, (6) AAA model tank, (7) outflow lines from the lower branches, (8) outflow lines from the upper branches, and (9) movable optical module.

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Figure 2

Overview of the PTV setup. Panel (a): Photograph of the image acquisition system. Its main components are labeled as (1) camera, (2) four way splitter prism, (3) mirrors and (4) optical rail. Panel (b): Photographic output showing the four different perspectives.

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Figure 6

Line plot comparisons of velocity components, panels (a)–(c), and pressure, panel (d), along the indicated polyline in Fig. 4

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Figure 7

Overview of the measurement volumes and the planar cross sections used for the comparison between the PTV and CFD velocity quantifications

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Figure 8

Comparison of experimental and computational velocity distributions along planar cross sections within the aneurysm sack as well as along indicated lines lying within these cross sections: Panels (a)–(d) X=0.19m and panels (e)–(h) X=0.22m

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Figure 9

Comparison of experimental and computational velocity distributions along planar cross sections within the aneurysm neck as well as along indicated lines lying within these cross sections: Panels (a)–(d) X=0.28m and panels (e)–(h) X=0.31m

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Figure 10

Comparison of experimental and computational velocity distributions along planar cross sections within the iliac bifurcation as well as along indicated lines lying within these cross sections: Panels (a)–(d) X=0.16m and panels (e)–(h) X=0.13m

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Figure 11

Normalized contour plot distributions upon the anterior and posterior sides of the aortic wall of pressure, panels (a) and (b), and wall shear stress magnitude, panels (c) and (d)

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