Influence of Shear-Thinning Blood Rheology on the Laminar-Turbulent Transition over a Backward Facing Step
Influence of Shear-Thinning Blood Rheology on the Laminar-Turbulent Transition over a Backward Facing Step
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DOI：
10.3390/fluids5020057
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发表时间：
2020-04
期刊：
影响因子：
1.9
通讯作者：
Nathaniel S. Kelly;H. Gill;A. Cookson;K. Fraser
中科院分区：
文献类型：
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作者：
Nathaniel S. Kelly;H. Gill;A. Cookson;K. Fraser
心血管疾病是全球死亡的主要原因，对有效、更安全的血液接触装置，包括瓣膜、支架和人工心脏的需求尚未得到满足。在这些情况下，再循环区域促进血栓形成，引发机械故障、神经功能障碍和梗死。向后台阶上的过渡流是这些流动条件的理想化模型;目的是了解非牛顿血液流变学对这种流动建模的影响。剪切稀化和牛顿流体的流动模拟进行了比较雷诺数（Re）覆盖的层流，过渡和湍流的全面范围内的第一次。对非定常雷诺平均纳维尔-斯托克斯（k − ω SST）和Smagorinsky大涡模拟（LES）进行了评估;只有LES正确预测了所有Re的回流区长度趋势。通过几个标准评估湍流转变，揭示了复杂的情况。瞬时湍流参数，如速度，表示延迟过渡：R e = 1600与R e = 2000，牛顿和剪切变稀过渡，分别。相反，当使用空间平均粘度上定义的Re时，剪切稀化模型在牛顿流体之下过渡。然而，回流区长度，平均流量参数，并没有表明两者之间的过渡Re的任何差异。这项工作表明，剪切稀化流变学可以解释在已发表的实验数据中看到的全血延迟转变，但这种延迟并不是全部。结果表明，为了准确地模拟过渡血流，从而使先进的心血管设备的设计，它是必不可少的，将剪切稀化流变学，并明确地模拟湍流涡流。
Cardiovascular diseases are the leading cause of death globally and there is an unmet need for effective, safer blood-contacting devices, including valves, stents and artificial hearts. In these, recirculation regions promote thrombosis, triggering mechanical failure, neurological dysfunction and infarctions. Transitional flow over a backward facing step is an idealised model of these flow conditions; the aim was to understand the impact of non-Newtonian blood rheology on modelling this flow. Flow simulations of shear-thinning and Newtonian fluids were compared for Reynolds numbers ( R e ) covering the comprehensive range of laminar, transitional and turbulent flow for the first time. Both unsteady Reynolds Averaged Navier–Stokes ( k − ω SST) and Smagorinsky Large Eddy Simulations (LES) were assessed; only LES correctly predicted trends in the recirculation zone length for all R e . Turbulent-transition was assessed by several criteria, revealing a complex picture. Instantaneous turbulent parameters, such as velocity, indicated delayed transition: R e = 1600 versus R e = 2000, for Newtonian and shear-thinning transitions, respectively. Conversely, when using a Re defined on spatially averaged viscosity, the shear-thinning model transitioned below the Newtonian. However, recirculation zone length, a mean flow parameter, did not indicate any difference in the transitional Re between the two. This work shows a shear-thinning rheology can explain the delayed transition for whole blood seen in published experimental data, but this delay is not the full story. The results show that, to accurately model transitional blood flow, and so enable the design of advanced cardiovascular devices, it is essential to incorporate the shear-thinning rheology, and to explicitly model the turbulent eddies.