Vorticity dynamics of a bileaflet mechanical heart valve in an axisymmetric aorta
Vorticity dynamics of a bileaflet mechanical heart valve in an axisymmetric aorta
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DOI：
10.1063/1.2743261
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发表时间：
2007-06-01
影响因子：
4.6
通讯作者：
Yoganathan, A. P.
中科院分区：
文献类型：
--
作者：
Dasi, L. P.;Ge, L.;Yoganathan, A. P.
我们提出了全面的粒子图像测速测量和直接数值模拟（DNS）的生理，脉动流通过临床质量双叶机械心脏瓣膜安装在一个理想的轴对称主动脉几何形状与突然扩张建模的主动脉窦区。瞬时和整体平均速度测量以及相关的统计学的瓣叶运动学的报告和分析串联，以阐明随后的流结构相互作用的速度和涡度场的结构。测量结果表明，在加速阶段的前半部分，流动是层流的，并且在循环之间是可重复的。瓣膜外壳剪切层卷起进入窦，并开始从窦壁提取相反符号的涡度。启动涡流结构从瓣叶脱落，并随着瓣叶剪切层变得波状和振荡而向下游平流。在流动加速的后半部分，叶片剪切层变得不稳定，并分解成两个冯卡门样的涡街。从瓣叶开始的旋涡脱落是显著的循环间涡度振荡增长的原因。在峰值流量时，外壳和瓣叶剪切层经历二次不稳定性，并迅速分解成混乱的、类似于湍流的状态，其中在流中出现多个小尺度旋涡结构。在减速和关闭阶段，所有大规模的相干流的功能消失，出现一个混乱的小尺度涡量场，即使在阀门关闭后仍然存在。在打开和关闭阶段期间瓣叶位置的概率密度函数表明，瓣叶位置在循环之间波动，在瓣膜关闭期间波动较大。DNS是通过从实验数据中规定瓣叶运动学来进行的。计算的瞬时涡量场与测量值非常吻合，特别是在加速阶段，此时流动保持连贯和可重复，瞬时比较是有意义的。对计算结果进行分析，首次阐明了通过双叶瓣三开口孔的脉动射流的复杂且高度三维的结构，并解释了二维涡量测量中记录的丰富流动现象。(c)2007年，美国物理学会。
We present comprehensive particle image velocimetry measurements and direct numerical simulation (DNS) of physiological, pulsatile flow through a clinical quality bileaflet mechanical heart valve mounted in an idealized axisymmetric aorta geometry with a sudden expansion modeling the aortic sinus region. Instantaneous and ensemble-averaged velocity measurements as well as the associated statistics of leaflet kinematics are reported and analyzed in tandem to elucidate the structure of the velocity and vorticity fields of the ensuing flow-structure interaction. The measurements reveal that during the first half of the acceleration phase, the flow is laminar and repeatable from cycle to cycle. The valve housing shear layer rolls up into the sinus and begins to extract vorticity of opposite sign from the sinus wall. A start-up vortical structure is shed from the leaflets and is advected downstream as the leaflet shear layers become wavy and oscillatory. In the second half of flow acceleration the leaflet shear layers become unstable and break down into two von Karman-like vortex streets. The onset of vortex shedding from the valve leaflets is responsible for the growth of significant cycle-to-cycle vorticity oscillations. At peak flow, the housing and leaflet shear layers undergo secondary instabilities and break down rapidly into a chaotic, turbulent-like state with multiple small-scale vortical structures emerging in the flow. During the deceleration and closing phases all large-scale coherent flow features disappear and a chaotic small-scale vorticity field emerges, which persists even after the valve has closed. Probability density functions of the leaflet position during opening and closing phases show that the leaflet position fluctuates from cycle to cycle with larger fluctuations evident during valve closure. The DNS is carried out by prescribing the leaflet kinematics from the experimental data. The computed instantaneous vorticity fields are in very good agreement with the measurements, especially during the accelerating phase when the flow remains coherent and repeatable and instantaneous comparisons are meaningful. The computed results are analyzed to elucidate for the first time the intricate and highly three-dimensional structure of the pulsatile jet through the triple-opening orifice of the bileaflet valve and explain the rich flow phenomena documented in the two-dimensional vorticity measurements. (c) 2007 American Institute of Physics.