Abstract Helical geometries to induce swirling and spiral flow in prosthetic grafts have been hypothesized as a possible way to improve the clinical outcomes in patients undergoing coronary artery bypass grafting. In this paper, the transient flow behavior in helical bypass conduits with two different curved flow paths (planar and nonplanar) was investigated. Numerical methods were used to examine the flow physics downstream of four idealized bypass conduits attached to an aorta. The flow field in the bypass conduits was examined based on a non-Newtonian blood-analog fluid with relevant physiological waveforms characterized by a Womersley number α of 2.13 and a mean Reynolds number Re mean of 107. The effects of nonplanar curvature and helicity were studied independently based on four idealized grafts. For all models, the axial flow downstream of the grafts resembles the oscillatory flow in straight tubes with a low α . The local secondary flow structures correspond closely to the strength of the swirling flow induced by the helical geometry. The helical conduit with a planar curved flow path in general consists of a pair of asymmetric vortices downstream. The introduction of a nonplanar curved flow path significantly increases the degree of asymmetry and leads to the transition from a double-vortex structure to a single swirling vortex flow. It is demonstrated that the swirling flow induced by the planar curvature promotes greater in-plane mixing downstream of the graft than the nonplanar curvature. However, the analysis of hemodynamic parameters reveals the effectiveness of a nonplanar curved flow path in the helical conduit in significantly elevating the overall mean wall shear stress. These findings demonstrate the possibility of using helical geometries and nonplanar curved flow paths in the design of external stents to independently control the mixing behavior and hemodynamic environment in coronary bypass conduits.

中文翻译：

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平面和非平面弯曲流路对冠状动脉旁路移植术螺旋导管血流动力学的影响：数值研究

摘要 在假体移植物中诱导涡流和螺旋流的螺旋几何结构已被假设为改善接受冠状动脉旁路移植术的患者的临床结果的一种可能方式。在本文中，研究了具有两种不同弯曲流路（平面和非平面）的螺旋旁通管道中的瞬态流动行为。数值方法用于检查连接到主动脉的四个理想化旁路导管下游的流动物理。基于具有相关生理波形的非牛顿血液模拟流体检查旁路管道中的流场，其特征是沃默斯利数 α 为 2.13，平均雷诺数 Re 平均值为 107。研究了非平面曲率和螺旋度的影响独立地基于四个理想化的移植物。对于所有型号，移植物下游的轴向流动类似于具有低 α 的直管中的振荡流动。局部二次流结构与螺旋几何引起的旋流强度密切对应。具有平面弯曲流动路径的螺旋导管通常由下游的一对不对称涡流组成。非平面弯曲流路的引入显着增加了不对称程度，并导致从双涡流结构转变为单旋涡流。结果表明，与非平面曲率相比，由平面曲率引起的涡流促进了移植物下游更大的平面内混合。然而，血液动力学参数的分析揭示了螺旋导管中的非平面弯曲流动路径在显着提高整体平均壁剪切应力方面的有效性。这些发现证明了在外部支架设计中使用螺旋几何形状和非平面弯曲流动路径来独立控制冠状动脉旁路导管中的混合行为和血流动力学环境的可能性。