Three-dimensional instabilities and transition of steady and pulsatile axisymmetric stenotic flows
Three-dimensional instabilities and transition of steady and pulsatile axisymmetric stenotic flows
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DOI：
10.1017/s0022112005004271
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发表时间：
2005-06-25
影响因子：
3.7
通讯作者：
Blackburn, HM
中科院分区：
文献类型：
--
作者：
Sherwin, SJ;Blackburn, HM
顺滑轴对称收缩的直管是动脉狭窄的理想表现。本文采用线性稳定性分析和直接数值模拟的方法，研究了75%光滑狭窄管内的定常流、加振荡分量的定常流和理想血管脉动流的三维不稳定性和向湍流的过渡。稳定流动经历弱coanda型壁面附着和亚临界分岔的湍流过渡，导致相对于雷诺数变化的滞后行为。脉动流通过亚临界倍周期分岔变得不稳定，该分岔涉及每个脉冲从喉部喷射出的涡环的交替倾斜。这些倾斜的涡旋环在管内通过自感机制迅速分解。虽然脉动流的线性不稳定模式在狭窄的下游具有最大能量，但我们已经通过直接数值模拟建立了击穿可以逐渐向上游传播，直到发生在狭窄的几个管径内，这与先前的实验观察结果一致。在本研究中使用的雷诺数下，过渡是局部的，再层化发生在更下游。对理想的生理脉动流中轴对称剪切层的可接受性也进行了非详尽的研究，结果表明它在部分脉冲周期中具有局部的对流不稳定性。
A straight tube with a smooth axisymmetric constriction is an idealized representation of a stenosed artery. We examine the three-dimensional instabilities and transition to turbulence of steady flow, steady flow plus an oscillatory component, and an idealized vascular pulsatile flow in a tube with a smooth 75% stenosis using both linear stability analysis and direct numerical simulation. Steady flow undergoes a weak Coanda-type wall attachment and turbulent transition through a subcritical bifurcation, leading to hysteretic behaviour with respect to changes in Reynolds number. The pulsatile flows become unstable through a subcritical period-doubling bifurcation involving alternating tilting of the vortex rings that are ejected from the throat with each pulse. These tilted vortex rings rapidly break down through a self-induction mechanism within the confines of the tube. While the linear instability modes for pulsatile flow have maximum energy well downstream of the stenosis, we have established using direct numerical simulation that breakdown can gradually propagate upstream until it occurs within a few tube diameters of the constriction, in agreement with previous experimental observations. At the Reynolds numbers employed in the present study, transition is localized, with relaminarization occurring further downstream. A non-exhaustive investigation has also been undertaken into the receptivity of the axisymmetric shear layer in the idealized physiological pulsatile flow, with the results suggesting it has localized convective instability over part of the pulse cycle.