PIV 기법을 이용한 선회유동의 혈류역학적 특성에 관한 실험적 연구

Abstract

Hemodynamic characteristics in an arterial blood vessel are closely related to the development of circular diseases because the morphological and functional expressions of the endothelial cells in the arterial wall are highly affected by surrounding fluid-dynamic forces (e.g. shear stress). Recently, the existence of swirling flow in an artery is frequently observed under in vivo conditions. However, the fluid-dynamic roles of swirling flow on the hemodynamic characteristics are not fully understood to date. Therefore, the effect of the swirling flow on the hemodynamic characteristics was investigated using a particle image velocimetry (PIV) technique. The effect of swirling inlet flow on the flow field in a stenosis model was experimentally investigated under steady-flow and pulsatile flow conditions. The swirling flow was found to significantly reduce the length of the recirculation flow region and enhance the early breakout of turbulent transition at the post-stenosis region. The pulsatile swirling flow provided various beneficial effects by reducing the negative wall shear stress, the oscillatory shear index, and the flow reverse coefficient at the post-stenosis channel. In addition, the overall energy dissipation rate of the flow is suppressed by the swirling component of the flow. The development of swirling flows in a helical vascular graft with various helical pitches and curvatures were investigated to obtain the optimum design of the swirling vascular graft. The swirling intensity and helicity of the swirling flow were found to have a linear relation with a modified Germano number (Gn*) of the helical graft. 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*, and the optimized helical design with a maximum Gn* was suggested for the future design of a vascular graft. The effects of swirling flow on the flow field in 45 degree end-to-side anastomosis are also investigated to reveal fluid-dynamic advantages of swirling flow in the vascular graft. Compared to non-swirling Poiseuille inlet flow usefully induces pathological hemodynamic features, such as high wall shear stress at the bed side and large flow separation at the toe side. The introduction of swirling flow is found to equalize the asymmetric wall shear stress distribution and reduce the peak magnitude of wall shear stress. In particular, the intermediate swirling intensity of S = 0.45 is found to induce the most uniform axial velocity and wall shear stress distributions compared with weaker or stronger swirling flows, which addresses the importance of proper selection of swirling intensity in the vascular graft to obtain optimum flow fields at the host vessel.