Rawat Digvijay S, Pourquie Mathieu, Poelma Christian
Laboratory for Aero & Hydrodynamics,Delft University of Technology,Leeghwaterstraat 21,Delft CA 2628, The Netherlandse-mail:
J Biomech Eng. 2019 Jun 1;141(6). doi: 10.1115/1.4043289.
Computational fluid dynamics (CFD) is a powerful method to investigate aneurysms. The primary focus of most investigations has been to compute various hemodynamic parameters to assess the risk posed by an aneurysm. Despite the occurrence of transitional flow in aneurysms, turbulence has not received much attention. In this article, we investigate turbulence in the context of abdominal aortic aneurysms (AAA). Since the clinical practice is to diagnose an AAA on the basis of its size, hypothetical axisymmetric geometries of various sizes are constructed. In general, just after the peak systole, a vortex ring is shed from the expansion region of an AAA. As the ring advects downstream, an azimuthal instability sets in and grows in amplitude thereby destabilizing the ring. The eventual breakdown of the vortex ring into smaller vortices leads to turbulent fluctuations. A residence time study is also done to identify blood recirculation zones, as a recirculation region can lead to degradation of the arterial wall. In some of the geometries simulated, the enhanced local mixing due to turbulence does not allow a recirculation zone to form, whereas in other geometries, turbulence had no effect on them. The location and consequence of a recirculation zone suggest that it could develop into an intraluminal thrombus (ILT). Finally, the possible impact of turbulence on the oscillatory shear index (OSI), a hemodynamic parameter, is explored. To conclude, this study highlights how a small change in the geometric aspects of an AAA can lead to a vastly different flow field.
计算流体动力学（CFD）是研究动脉瘤的一种强大方法。大多数研究的主要重点是计算各种血流动力学参数，以评估动脉瘤带来的风险。尽管动脉瘤中会出现过渡流，但湍流并未受到太多关注。在本文中，我们在腹主动脉瘤（AAA）的背景下研究湍流。由于临床实践是根据其大小来诊断AAA，因此构建了各种大小的假设轴对称几何模型。一般来说，在收缩期峰值刚过后，一个涡环从AAA的扩张区域脱落。当涡环向下游平流时，方位不稳定性开始出现并振幅增大，从而使涡环失稳。涡环最终分解为较小的涡旋会导致湍流波动。还进行了停留时间研究以识别血液再循环区域，因为再循环区域会导致动脉壁退化。在一些模拟的几何模型中，由于湍流导致的局部混合增强不允许形成再循环区域，而在其他几何模型中，湍流对它们没有影响。再循环区域的位置和结果表明它可能发展为腔内血栓（ILT）。最后，探讨了湍流对血流动力学参数振荡剪切指数（OSI）的可能影响。总之，本研究强调了AAA几何方面的微小变化如何导致截然不同的流场。
