Al-Azawy Mohammed G, Turan A, Revell A
a School of Mechanical, Aerospace and Civil Engineering, The University of Manchester , Manchester , UK.
b Mechanical Engineering Department, College of Engineering, Wasit University , Wasit , Iraq.
Comput Methods Biomech Biomed Engin. 2016 Feb;19(3):271-285. doi: 10.1080/10255842.2015.1015527. Epub 2015 Mar 27.
Computational fluid dynamics (CFD) is applied to study the unsteady flow inside a pulsatile pump left ventricular assist device, in order to assess the sensitivity to a range of commonly used turbulence models. Levels of strain and wall shear stress are directly relevant to the evaluation of risk from haemolysis and thrombosis, and thus understanding the sensitivity to these turbulence models is important in the assessment of uncertainty in CFD predictions. The study focuses on a positive displacement or pulsatile pump, and the CFD model includes valves and moving pusher plate. An unstructured dynamic layering method was employed to capture this cyclic motion, and valves were simulated in their fully open position to mimic the natural scenario, with in/outflow triggered at control planes away from the valves. Six turbulence models have been used, comprising three relevant to the low Reynolds number nature of this flow and three more intended to investigate different transport effects. In the first group, we consider the shear stress transport (SST) [Formula: see text] model in both its standard and transition-sensitive forms, and the 'laminar' model in which no turbulence model is used. In the second group, we compare the one equation Spalart-Almaras model, the standard two equation [Formula: see text] and the full Reynolds stress model (RSM). Following evaluation of spatial and temporal resolution requirements, results are compared with available experimental data. The model was operated at a systolic duration of 40% of the pumping cycle and a pumping rate of 86 BPM (beats per minute). Contrary to reasonable preconception, the 'transition' model, calibrated to incorporate additional physical modelling specifically for these flow conditions, was not noticeably superior to the standard form of the model. Indeed, observations of turbulent viscosity ratio reveal that the transition model initiates a premature increase of turbulence in this flow, when compared with both experimental and higher order numerical results previously reported in the literature. Furthermore, the RSM is indicated to provide the most accurate prediction over much of the flow, due to its ability to more correctly account for three-dimensional effects. Finally, the clinical relevance of the results is reported along with a discussion on the impact of such modelling uncertainties.
应用计算流体动力学（CFD）研究脉动泵式左心室辅助装置内的非定常流动，以评估对一系列常用湍流模型的敏感性。应变水平和壁面剪应力与溶血和血栓形成风险的评估直接相关，因此了解对这些湍流模型的敏感性对于评估CFD预测中的不确定性很重要。该研究聚焦于容积式或脉动泵，CFD模型包括瓣膜和移动推板。采用非结构化动态分层方法来捕捉这种循环运动，瓣膜在完全打开位置进行模拟以模拟自然场景，在远离瓣膜的控制平面触发进出流。使用了六种湍流模型，包括三种与该流动的低雷诺数特性相关的模型以及另外三种旨在研究不同输运效应的模型。在第一组中，我们考虑标准形式和过渡敏感形式的剪切应力输运（SST）[公式：见原文]模型，以及未使用湍流模型的“层流”模型。在第二组中，我们比较单方程Spalart - Almaras模型、标准双方程[公式：见原文]模型和完整雷诺应力模型（RSM）。在评估空间和时间分辨率要求之后，将结果与可用的实验数据进行比较。该模型在泵血周期的收缩期持续时间为40%且泵血速率为86次/分钟（每分钟心跳次数）的条件下运行。与合理的先入之见相反，针对这些流动条件校准以纳入额外物理建模的“过渡”模型并不明显优于该模型的标准形式。实际上，对湍流粘度比的观察表明，与文献中先前报道的实验和高阶数值结果相比，过渡模型在此流动中引发了湍流的过早增加。此外，由于RSM能够更正确地考虑三维效应，表明它在大部分流动中提供了最准确的预测。最后，报告了结果的临床相关性，并讨论了此类建模不确定性的影响。
