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Fluid-dynamic optimal design of helical vascular graft for stenotic disturbed flow.

Ha H, Hwang D, Choi WR, Baek J, Lee SJ - PLoS ONE (2014)

Bottom Line: Results showed that the swirling intensity and helicity of the swirling flow have a linear relation with a modified Germano number (Gn*) of the helical pipe.In addition, the swirling flow generated a beneficial flow structure at the stenosis by reducing the size of the recirculation flow under steady and pulsatile flow conditions.Therefore, the beneficial effects of a helical graft on the flow field can be estimated by using the magnitude of Gn*.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, Republic of Korea.

ABSTRACT
Although a helical configuration of a prosthetic vascular graft appears to be clinically beneficial in suppressing thrombosis and intimal hyperplasia, an optimization of a helical design has yet to be achieved because of the lack of a detailed understanding on hemodynamic features in helical grafts and their fluid dynamic influences. In the present study, the swirling flow in a helical graft was hypothesized to have beneficial influences on a disturbed flow structure such as stenotic flow. The characteristics of swirling flows generated by helical tubes with various helical pitches and curvatures were investigated to prove the hypothesis. The fluid dynamic influences of these helical tubes on stenotic flow were quantitatively analysed by using a particle image velocimetry technique. Results showed that the swirling intensity and helicity of the swirling flow have a linear relation with a modified Germano number (Gn*) of the helical pipe. In addition, the swirling flow generated a beneficial flow structure at the stenosis by reducing the size of the recirculation flow under steady and pulsatile flow conditions. Therefore, the beneficial effects of a helical graft on the flow field can be estimated by using the magnitude of Gn*. Finally, an optimized helical design with a maximum Gn* was suggested for the future design of a vascular graft.

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Computational grid and block arrangement.
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pone-0111047-g004: Computational grid and block arrangement.

Mentions: The computational grid and block arrangement are shown in figure 4. The grid system composed of hexahedral unstructured meshes was generated by the mesh generation software ICEM CFD. The flow region was discretized from a five-block structure, that is, the O-type grid. The grid consisted of 96 points in an angular direction. Thus, 24 points made up each side of the rectangular grid section (see grid block 1 in figure 4). Approximately 790 points were generated in the axial direction. The grid resolution was set to high near the wall. The minimum grid spacing on the walls was set to 5×10−5 m for the accurate estimation of viscous flow without a wall function method. The total number of grids was approximately 2.5×106; the exact numbers slightly varied according to the curvature and pitch of the model. Given that solutions and their stability can be influenced by the number of grids, the grid structure was optimally selected through a grid dependency test. Grid independence was verified by increasing the number of computational grids from 5×105 to 6×106 and by examining the helicity of the flow at the outlet. The optimum number of grids was determined to be 2.5×106 when the change in helicity change was less than 0.2%.


Fluid-dynamic optimal design of helical vascular graft for stenotic disturbed flow.

Ha H, Hwang D, Choi WR, Baek J, Lee SJ - PLoS ONE (2014)

Computational grid and block arrangement.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4215892&req=5

pone-0111047-g004: Computational grid and block arrangement.
Mentions: The computational grid and block arrangement are shown in figure 4. The grid system composed of hexahedral unstructured meshes was generated by the mesh generation software ICEM CFD. The flow region was discretized from a five-block structure, that is, the O-type grid. The grid consisted of 96 points in an angular direction. Thus, 24 points made up each side of the rectangular grid section (see grid block 1 in figure 4). Approximately 790 points were generated in the axial direction. The grid resolution was set to high near the wall. The minimum grid spacing on the walls was set to 5×10−5 m for the accurate estimation of viscous flow without a wall function method. The total number of grids was approximately 2.5×106; the exact numbers slightly varied according to the curvature and pitch of the model. Given that solutions and their stability can be influenced by the number of grids, the grid structure was optimally selected through a grid dependency test. Grid independence was verified by increasing the number of computational grids from 5×105 to 6×106 and by examining the helicity of the flow at the outlet. The optimum number of grids was determined to be 2.5×106 when the change in helicity change was less than 0.2%.

Bottom Line: Results showed that the swirling intensity and helicity of the swirling flow have a linear relation with a modified Germano number (Gn*) of the helical pipe.In addition, the swirling flow generated a beneficial flow structure at the stenosis by reducing the size of the recirculation flow under steady and pulsatile flow conditions.Therefore, the beneficial effects of a helical graft on the flow field can be estimated by using the magnitude of Gn*.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, Republic of Korea.

ABSTRACT
Although a helical configuration of a prosthetic vascular graft appears to be clinically beneficial in suppressing thrombosis and intimal hyperplasia, an optimization of a helical design has yet to be achieved because of the lack of a detailed understanding on hemodynamic features in helical grafts and their fluid dynamic influences. In the present study, the swirling flow in a helical graft was hypothesized to have beneficial influences on a disturbed flow structure such as stenotic flow. The characteristics of swirling flows generated by helical tubes with various helical pitches and curvatures were investigated to prove the hypothesis. The fluid dynamic influences of these helical tubes on stenotic flow were quantitatively analysed by using a particle image velocimetry technique. Results showed that the swirling intensity and helicity of the swirling flow have a linear relation with a modified Germano number (Gn*) of the helical pipe. In addition, the swirling flow generated a beneficial flow structure at the stenosis by reducing the size of the recirculation flow under steady and pulsatile flow conditions. Therefore, the beneficial effects of a helical graft on the flow field can be estimated by using the magnitude of Gn*. Finally, an optimized helical design with a maximum Gn* was suggested for the future design of a vascular graft.

Show MeSH
Related in: MedlinePlus