Fukushima T, Azuma T
Biorheology. 1982;19(1/2):143-54. doi: 10.3233/bir-1982-191-217.
In order to elucidate the fluid dynamic feature of arterial blood flow, the present flow visualization study was carried out with various transparent blood vessel models having a protuberance, a bifurcation, or branchings. The observed flow patterns could be understood in terms of occurrence of a secondary flow, named the horseshoe vortex. The mode of generation of the horseshoe vortex in a tube with a protuberance projecting into the boundary layer was explained as follows. A radial pressure gradient toward the tube wall was produced along the upstream surface of the protuberance because of the interaction between the viscous sheared flow and the wall. This pressure gradient made fluid particles turn round downward directly before the obstacle. Then they curled round on themselves and formed a bound vortex tube, the horseshoe vortex, which in turn passed round the front of the protuberance in both directions. In a tube with a Y-shaped bifurcation or rectangular side branch, the flow divider at the branching site acted in place of the protuberance to produce a vortex tube similar in pattern to the horseshoe vortex. The vortex tube extended from the high pressure region, i. e. the apex of the flow divider, to the low pressure region, i. e. the lateral margin of the branch orifice, and generated swirling secondary flows in the main and branched tubes. These results suggested that the following mechanical factors might initiate or facilitate athero- and thrombogenesis: collision of blood cells captured by the horseshoe vortex with blood vessel walls, the interaction of the walls and blood cells due to turbulence, and the occurrence of localized high wall shear stresses.
为了阐明动脉血流的流体动力学特征，本研究采用了各种带有凸起、分叉或分支的透明血管模型进行流动可视化研究。观察到的流动模式可以通过一种名为马蹄涡的二次流的产生来理解。在一根有突出物突入边界层的管道中，马蹄涡的产生方式如下所述。由于粘性剪切流与管壁之间的相互作用，沿着突出物的上游表面产生了一个朝向管壁的径向压力梯度。这个压力梯度使流体颗粒在障碍物前方直接向下转向。然后它们自身卷曲形成一个束缚涡管，即马蹄涡，该涡管继而在两个方向上绕过突出物的前端。在具有Y形分叉或矩形侧支的管道中，分叉部位的分流器起到了突出物的作用，产生了一个模式与马蹄涡相似的涡管。该涡管从高压区域，即分流器的顶点，延伸到低压区域，即分支孔口的侧缘，并在主管道和分支管道中产生旋转的二次流。这些结果表明，以下力学因素可能引发或促进动脉粥样硬化和血栓形成：被马蹄涡捕获的血细胞与血管壁的碰撞、由于湍流导致的血管壁与血细胞的相互作用以及局部高壁面剪切应力的出现。
