Nonlinear hydrodynamic instability and turbulence in pulsatile flow
Nonlinear hydrodynamic instability and turbulence in pulsatile flow
复制标题
脉动流中的非线性流体动力学不稳定性和湍流
DOI：
10.1073/pnas.1913716117
复制
发表时间：
2020-05-26
影响因子：
11.1
通讯作者：
Hof, Bjorn
中科院分区：
文献类型：
--
作者：
Xu, Duo;Varshney, Atul;Hof, Bjorn
血管内壁，即内皮，具有剪切敏感性。波动的剪切应力和紊乱的血流是细胞功能障碍的原因，导致动脉粥样硬化病变的发展。在此，我们发现了一种非线性流体动力不稳定性，它会导致心血管血流参数范围内的无序运动。在流动减速过程中，微小的几何缺陷会引发螺旋涡模式，随后分解成湍流的爆发。由此产生的波动剪切应力水平在加速过程中突然下降，流动再层化开始。观察到的不稳定性发生在比线性不稳定性或经典湍流路径低得多的流量下。我们的研究表明，在脉动/心血管血流中，运动紊乱比先前考虑的稳定性更常见。只要速度适中，通过管状几何形状的脉动流就是层流。这也被认为特别适用于心血管流动，其中惯性力通常太低而无法维持湍流。另一方面，流动不稳定和波动剪切应力被认为是多种心血管疾病的原因。在这里，我们报告了脉动管流的非线性不稳定性机制，该机制在低流量下引起湍流爆发。发现小而有限的几何畸变在流动减速时激发了由螺旋涡组成的状态。由此产生的流型在规模上迅速增长，分解为湍流，并在流动加速时最终恢复为层流。这种情况会在每个脉动周期中引起剪切应力波动和流体反转。这种不稳定的条件会对血管产生不利影响，并已被证明会促进对剪切应力敏感的内皮细胞层的炎症和功能障碍。
Significance The inner lining of blood vessels, the endothelium, is shear sensitive. Fluctuating shear stresses and disordered flow are responsible for cellular dysfunction, leading to the development of atherosclerotic lesions. We here identify a nonlinear hydrodynamic instability that gives rise to disordered motion in the parameter range of cardiovascular flow. During flow deceleration small geometrical imperfections trigger a helical vortex pattern that subsequently breaks down into bursts of turbulence. The resulting fluctuating shear stress level drops abruptly during the acceleration where flow relaminarization sets in. The observed instability occurs at considerably lower flowrates than either the linear instability or the classic route to turbulence. Our study shows that disordered motion is more common in pulsatile/cardiovascular flows than previous stability considerations suggest. Pulsating flows through tubular geometries are laminar provided that velocities are moderate. This in particular is also believed to apply to cardiovascular flows where inertial forces are typically too low to sustain turbulence. On the other hand, flow instabilities and fluctuating shear stresses are held responsible for a variety of cardiovascular diseases. Here we report a nonlinear instability mechanism for pulsating pipe flow that gives rise to bursts of turbulence at low flow rates. Geometrical distortions of small, yet finite, amplitude are found to excite a state consisting of helical vortices during flow deceleration. The resulting flow pattern grows rapidly in magnitude, breaks down into turbulence, and eventually returns to laminar when the flow accelerates. This scenario causes shear stress fluctuations and flow reversal during each pulsation cycle. Such unsteady conditions can adversely affect blood vessels and have been shown to promote inflammation and dysfunction of the shear stress-sensitive endothelial cell layer.