König C S, Clark C, Mokhtarzadeh-Dehghan M R
Department of Manufacturing and Engineering Systems, Brunel University, Uxbridge, Middlesex, UK.
Med Eng Phys. 1999 Jan;21(1):53-64. doi: 10.1016/s1350-4533(98)00084-8.
Prior to this study, a clinical prototype of a sac-type ventricular assist device (VAD) was investigated experimentally, using both flow visualisation and Laser Doppler anemometry (LDA), in order to optimise its geometry. As poor optical access precluded the experimental investigation of the flow in some areas of the prototype VAD, computational fluid dynamics (CFD) was used in the present work. Flow patterns during one full pumping cycle were investigated in a simplified model of the VAD. The numerical solutions were compared with experimental results from an identical physical model. The model consists of the hemispherical cylinder and two attached tubes for the inflow and outflow. Instead of a diaphragm in the clinical device, which deforms non-uniformly during pumping, a piston with a matching hemispherical crown was used. A finite volume method was employed to solve the governing equations for the three-dimensional, unsteady, laminar flow of an incompressible, Newtonian fluid. The general flow features were predicted very well by the simulation, with some differences in the details of the flow structures. This allows the conclusion that CFD can be used to facilitate improvement of the design of the clinical device. The comparison of one-component velocity time histories at selected points showed that the predicted velocities were approximately 20-50% lower than those measured by LDA. Such underprediction would lead to erroneous results for particle residence times and may result in an underestimation of wall shear stresses.
在本研究之前，为优化其几何形状，使用流动可视化和激光多普勒测速仪（LDA）对囊式心室辅助装置（VAD）的临床原型进行了实验研究。由于光学通路不佳妨碍了对原型VAD某些区域内流动的实验研究，因此在本工作中使用了计算流体动力学（CFD）。在VAD的简化模型中研究了一个完整泵送周期内的流动模式。将数值解与来自相同物理模型的实验结果进行了比较。该模型由半球形圆柱体和两个用于流入和流出的连接管组成。临床装置中使用的隔膜在泵送过程中变形不均匀，这里使用了一个带有匹配半球形顶部的活塞来替代。采用有限体积法求解不可压缩牛顿流体三维非定常层流的控制方程。模拟很好地预测了总体流动特征，只是在流动结构细节上存在一些差异。由此可以得出结论，CFD可用于促进临床装置设计的改进。在选定位置对单分量速度时间历程的比较表明，预测速度比LDA测量的速度低约20% - 50%。这种预测不足会导致颗粒停留时间的错误结果，并可能导致壁面剪应力的低估。
