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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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The effect of swirling flow on the length of flow reattachment (L/D) and WSS at the post-stenosis.(a) Velocity contours and streamlines at the post-stenosis. Poiseuille and swirling inlet flows are generated by the straight and helical tubes (Rc/R0 = 0.6, H/R0 = 4) at Re = 814. (b) distribution of normalized WSS at the post-steonsis. WSS was normalized by the WSS that would exist in Poiseuille flow in a conduit at the same Re. The error bars indicate 95% confidence limits and only half of them are shown for clarity. (c) variations of L/D with respect to S, (d) variations of L/D with respect to Gn*. Mean standard deviations of L/D = 0.39.
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pone-0111047-g012: The effect of swirling flow on the length of flow reattachment (L/D) and WSS at the post-stenosis.(a) Velocity contours and streamlines at the post-stenosis. Poiseuille and swirling inlet flows are generated by the straight and helical tubes (Rc/R0 = 0.6, H/R0 = 4) at Re = 814. (b) distribution of normalized WSS at the post-steonsis. WSS was normalized by the WSS that would exist in Poiseuille flow in a conduit at the same Re. The error bars indicate 95% confidence limits and only half of them are shown for clarity. (c) variations of L/D with respect to S, (d) variations of L/D with respect to Gn*. Mean standard deviations of L/D = 0.39.

Mentions: The effect of the swirling flow in the helical tube on the post-stenosis flow was experimentally investigated using a PIV technique. The velocity contours and streamlines in figure 12a show that the swirling flow created by the helical tube (Rc/R0 = 0.6, H/R0 = 4) significantly reduces the length of the jet flow and the recirculation area at the post-stenosis. As shown in figure 12b, the recirculation area is characterized by low negative WSS distribution, which is caused by the slow retrograde flow. While swirling flow has no significant influence on maximum and minimum magnitudes of the WSS, total area of the low WSS region is significantly reduced by the introduction of swirling flow due to reduction of the recirculation flow.


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)

The effect of swirling flow on the length of flow reattachment (L/D) and WSS at the post-stenosis.(a) Velocity contours and streamlines at the post-stenosis. Poiseuille and swirling inlet flows are generated by the straight and helical tubes (Rc/R0 = 0.6, H/R0 = 4) at Re = 814. (b) distribution of normalized WSS at the post-steonsis. WSS was normalized by the WSS that would exist in Poiseuille flow in a conduit at the same Re. The error bars indicate 95% confidence limits and only half of them are shown for clarity. (c) variations of L/D with respect to S, (d) variations of L/D with respect to Gn*. Mean standard deviations of L/D = 0.39.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0111047-g012: The effect of swirling flow on the length of flow reattachment (L/D) and WSS at the post-stenosis.(a) Velocity contours and streamlines at the post-stenosis. Poiseuille and swirling inlet flows are generated by the straight and helical tubes (Rc/R0 = 0.6, H/R0 = 4) at Re = 814. (b) distribution of normalized WSS at the post-steonsis. WSS was normalized by the WSS that would exist in Poiseuille flow in a conduit at the same Re. The error bars indicate 95% confidence limits and only half of them are shown for clarity. (c) variations of L/D with respect to S, (d) variations of L/D with respect to Gn*. Mean standard deviations of L/D = 0.39.
Mentions: The effect of the swirling flow in the helical tube on the post-stenosis flow was experimentally investigated using a PIV technique. The velocity contours and streamlines in figure 12a show that the swirling flow created by the helical tube (Rc/R0 = 0.6, H/R0 = 4) significantly reduces the length of the jet flow and the recirculation area at the post-stenosis. As shown in figure 12b, the recirculation area is characterized by low negative WSS distribution, which is caused by the slow retrograde flow. While swirling flow has no significant influence on maximum and minimum magnitudes of the WSS, total area of the low WSS region is significantly reduced by the introduction of swirling flow due to reduction of the recirculation flow.

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