Institute for Computational Physics, University of Stuttgart, Allmandring 3, 70569, Stuttgart, Germany.
Biomech Model Mechanobiol. 2020 Feb;19(1):113-131. doi: 10.1007/s10237-019-01199-1. Epub 2019 Jul 30.
Onset of flow transition in a sinusoidally oscillating flow through a rigid, constant area circular pipe with a smooth sinusoidal obstruction in the center of the pipe is studied by performing direct numerical simulations, with resolutions close to the Kolmogorov microscales. The studied pipe is stenosed in the center with a 75% reduction in area in two distinct configurations-one that is symmetric to the axis of the parent pipe and the other that is offset by 0.05 diameters to introduce an eccentricity, which disturbs the flow thereby triggering the onset of flow transition. The critical Reynolds number at which the flow transitions to turbulence for a zero-mean oscillatory flow through a stenosis is shown to be nearly tripled in comparison with studies of pulsating unidirectional flow through the same stenosis. The onset of transition is further explored with three different flow pulsation frequencies resulting in a total of 90 simulations conducted on a supercomputer. It is found that the critical Reynolds number at which the oscillatory flow transitions is not affected by the pulsation frequencies. The locations of flow breakdown and re-stabilization post-stenosis are, however, respectively shifted closer to the stenosis throat with increasing pulsation frequencies. The results show that oscillatory physiological flows, while more stable, exhibit fluctuations due to geometric complexity and have implications in studies of dispersion and solute transport in the cerebrospinal fluid flow and understanding of pathological conditions.
通过对中心存在光滑正弦形障碍物的刚性定常圆管内正弦振荡流进行直接数值模拟，研究了流动转捩的起始。模拟分辨率接近柯尔莫哥洛夫微尺度。研究的圆管在中心处狭窄，面积缩小 75%，有两种不同的结构：一种是相对于母管的轴线对称的，另一种是偏心 0.05 直径的，从而扰乱了流动，从而引发流动转捩的起始。与通过相同狭窄处的脉动单向流的研究相比，零均值振荡流通过狭窄处转捩到湍流的临界雷诺数几乎增加了两倍。通过三种不同的流动脉动频率进一步探讨了转捩的起始，总共在超级计算机上进行了 90 次模拟。结果表明，振荡流的转捩临界雷诺数不受脉动频率的影响。然而，狭窄后的流动崩溃和再稳定的位置分别随着脉动频率的增加而更靠近狭窄喉部移动。结果表明，尽管振荡生理流更稳定，但由于几何复杂性会出现波动，这对脑脊液流动中的弥散和溶质输运研究以及病理条件的理解具有重要意义。
