Bifurcating vessel is a characteristic feature of biological systems such as arteries in the cardiovascular system and pulmonary airways. In cardiovascular system, the bifurcations are often asymmetric, flow is pulsatile, and the fluid, blood, shows a complex rheology. In this work, we study computationally pulsatile flow in planar symmetric and asymmetric, three-dimensional bifurcating vessels. The fluid is considered to be Newtonian as well as non-Newtonian following Carreau's model, and the results are compared. While the flow divides in the two daughter tubes equally in symmetric bifurcations, the flow distribution is time-dependent during a cardiac cycle in asymmetric bifurcations. The flow pattern changes significantly during a cardiac cycle. The secondary flow caused by a turning streamline is analyzed in terms of secondary velocity, vorticity, and helicity. Significant variation is observed in the secondary flow in a cardiac cycle. The secondary flow is observed to be stronger at the start of the diastole despite reduced flow rate. The separated flow on the outer wall causes a significant reduction in time-averaged wall shear stress, a biomarker to assess the possibility of atherosclerotic plaque development. While no significant difference is observed in the results obtained for Newtonian and non-Newtonian fluids at high shear rates, for example, during systole, significant differences are observed when the shear rate is low, during diastole or in the separation region. The velocity profile for the non-Newtonian fluid is observed to be flatter than that for Newtonian fluid. Further oscillatory shearing index, relative residence time, the parameters used as biomarkers are presented.

中文翻译：

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对称和非对称分叉血管中的脉动流动动力学

分叉血管是生物系统的一个特征，例如心血管系统和肺气道中的动脉。在心血管系统中，分叉通常是不对称的，流动是脉动的，流体、血液表现出复杂的流变学。在这项工作中，我们研究了平面对称和不对称的三维分叉血管中的计算脉动流。根据 Carreau 模型，流体被认为是牛顿流体和非牛顿流体，并比较结果。虽然在对称分叉中的两个子管中的流量均等分配，但在不对称分叉中的心动周期中，流量分布与时间相关。在心动周期中，流动模式发生显着变化。由转弯流线引起的二次流用二次速度分析，涡度和螺旋度。在心动周期中的二次流中观察到显着变化。尽管流速降低，但在舒张开始时观察到二次流更强。外壁上的分离流导致时间平均壁剪切应力显着降低，这是评估动脉粥样硬化斑块发展可能性的生物标志物。虽然在高剪切速率下，例如在收缩期，在牛顿流体和非牛顿流体获得的结果中没有观察到显着差异，但在剪切速率低时、舒张期或分离区域中观察到显着差异。观察到非牛顿流体的速度剖面比牛顿流体的速度剖面更平坦。进一步振荡剪切指数、相对停留时间、