| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1990: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1989: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
It is well known that the variation of wall shear stress, i. e. momentum transfer rate, is closely associated with the disease of vascular wall such as atherosclerosis. In general, the distribution of wall shear stress is affected by the vessel geometric shape.
In the present study, the distribution of wall shear stress in the 45-deg bifurcation model during steady flow has been measured by the electrochemical method which is based on a diffusion-controlled reaction of ferricyanide ion to ferrocyanide ion at the platinum electrode (diameter=0.5mm). Approximately 200 test electrodes were embedded in vessel wall. The model made of plexiglas consisted of the parent vessel (D_0=24mm) and the daughter vessel (D_1=14mm). The curvature of outer wall in daughter vessel and flow divider (apex) was R_D=3.5D_0 and R_C=D_0/8, respectively. This bifurcation models the arterial site from abdominal aorta to inferior mesenteric artery. The experiment has been carried out in the range of Reynolds number
… More
500, 800 and 1200, and in both condition of steady and pulsating flow. In pulsating flow, the non-dimensional frequency is (D_0/2) <square root>omega/nu=6. The ratio of flow rate in daughter vessel to total flow rate in upstream parent vessel is about 0.25 which corresponds to the ratio of cross sectional area in each downstream vessel. The flow pattern was visualized by a dye injection.
In steady flow, the flow through this bifurcation was characterized at the outer wall of daughter vessel. at outer wall of parent vessel and near the flow divider. At the outer wall of daughter vessel, the wall shear stress changes periodically. This periodical variation relates to double helical flow which flows into daughter vessel from the upstream parent vessel near vessel wall. At this wall the flow does not separate. At the outer wall of parent vessel, the separation region occurs near bifurcation point, and therefore the wall shear stress would be negative there. At the flow divider, after the wall shear stress becomes maximum at apex, it decreases and asymptotically approaches the wall shear stress of downstream Poiseuille flow
In pulsating flow, the variation of wall shear stress at maximum flow rate is greater than that corresponding steady flow, and vise versa. The time variation at each wall site is remarkably near the bifurcation point. Less
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