应用CFD研究叶轮设计对人工心脏泵内流场的影响

溶血是叶轮血泵常见的一种血液破坏现象，而造成这种现象的内在原因是血液的动力学行为。本研究针对基于流线型设计的叶轮血泵和一种直叶片血泵，应用CFD对其内部流场进行了数值模拟，并通过溶血实验对结果进行了验证。研究结果表明，流线型叶轮血泵内的流动模式符合流线型设计理论，与直叶片叶轮血泵相比，它的溶血较小，更符合血液动力学要求。可以认为，在相同的边界条件下，流线型叶轮血泵具有更好的血液相容性，不容易造成血液破坏。     

基于粒子图像测速技术的血泵内流场研究

自制外触发同步系统,应用二维粒子图像测速技术技术(PIV)实现了流线型叶轮血泵和直叶片叶轮血泵的内流场的测量,并分析叶轮设计和运行条件对血泵内流场和血液相容性的影响.实验结果表明:基于外触发同步的PIV系统实现了对血泵同一流道的流速信息的连续采样;血泵内的绝对速度和相对速度分布随着叶轮设计、流量和进出口压差而改变.在设计工况(4 L/min,100 mmHg)下,流线型叶轮血泵流道内的流动模式较为规则,而直叶片血泵的流动模式则出现了明显的旋涡、回流和流动分离等现象.根据血液动力学理论,在设计工况下,流线型叶轮血泵具有较好的血液相容性.     

基于CFD的离心式人工心脏泵的溶血预测方法

溶血的定量评价对于人工心脏泵的设计和研究十分重要.本研究应用CFD（computational fluid dynamics）技术,针对两种叶轮设计的离心血泵进行了数值模拟,计算得到了其内部的流线分布.根据溶血、切应力和暴露时间三者之间的幂函数模型,对血泵的溶血进行了预测.最后,用溶血实验结果进行了验证.结果表明,在相同的边界条件下,流线型叶轮泵内的溶血值要小于直叶片叶轮泵,与溶血实验结果一致.可见,应用CFD实现溶血的定量计算是可行的,溶血、切应力和暴露时间之间的幂函数模型能较好地反映血泵的溶血性能.     

流线型设计在人工心脏的应用

血栓形成是当前人工心脏研究中急需解决的首要问题。最易形成血栓的区域是涡流区、高切应力区、滞流区和重复附着区(reattachment)。从流变学和血液动力学出发,这些不规则的流动模式可以通过改善边界条件而消除。流线型设计便是其中的一种方法。本文介绍流线型设计在离心型叶轮血泵和排积型隔膜血泵的应用和结果。理论和实践均表明:在飞机、船舶和汽车制造业广泛应用的流线型设计,也是人工心脏抗血栓形成的通用技术。     

无叶片离心泵结构对体外循环关键参数的影响

目的探讨无叶片离心泵结构和体外循环关键参数之间的关系,为无叶片离心泵的优化设计提供理论依据和实践参考。方法采用计算流体动力学（computational fluid dynamics,CFD）方法对无叶片离心泵进行数值模拟,分析离心泵的结构和转速与血液流量、泵内流动状态、预充量之间的关系。结果叶轮与蜗壳之间距离一定时,两层叶轮结构比一层叶轮结构驱动血液能力强,但是预充量大;进出口导管直径小,有利于调节流量;泵体结构和叶轮转速影响泵内的血液速度分布,从而会对血液造成不同程度的破坏。结论无叶片离心泵结构和叶轮转速对体外循环流量的控制、泵内血液速度分布、预充量有很大影响。     

运用三维数值模拟对人工心脏轴流血泵的设计和改进

目的 设计、开发在性能上能满足左心室辅助要求的轴流式心脏辅助泵。方法 使用Numeca软件和运用现代叶轮机设计技术对人工心脏轴流血泵的内部流场情况进行数值模拟，对局部的回流、倒流和涡流现象进行改进，根据最终的数值模拟结果对流道和叶型进行设计。然后，对外轴承方案也进行数值模拟。结果 通过Numeca软件的数值模拟后改进，大大抑制了轴流泵内部的混乱流动，改善了流动状况，提高了轴流泵的血液相容性。对外轴承方案进行初步的数值模拟结果表明，随着机匣扩展角的增加，倒流现象逐渐得到抑制，流动情况得到改善。结论 本研究应用Numeca软件和现代叶轮机设计技术开发设计的轴流泵，在流体力学性能和血液相容性能上达到了左心室心脏泵的辅助要求。具有创新性的外轴承方案值得进一步探索。     

心肌桥壁冠状动脉血液动力学数值模拟

目的数值模拟心肌桥壁冠状动脉血液动力学,探索心肌桥壁冠状动脉近心端易发生动脉粥样硬化的血液动力学机理。方法建立随心搏运动的局部狭窄直圆管模型模拟心肌桥壁冠状动脉形态学,管壁为薄壁线弹性体,血流遵循不可压缩牛顿流体的一维管流方程组,用Lax-Wendroff方法数值求解。结果心肌桥壁冠状动脉血液动力学与正常冠状动脉血液动力学相比有很大差异,血流量#壁切应力和壁切应力梯度均不同。在心肌桥壁冠状动脉中,近心端壁切应力及壁切应力梯度的变化要远大于远心端。对于有两段心肌桥的情况,它们的壁切应力和壁切应力梯度变化趋势基本一致,但距心室较远的心肌桥,其壁切应力和壁切应力梯度要大于靠近心室的那段心肌桥,且随时间的变化程度也更剧烈。结论数值模拟结果表明,心肌桥壁冠状动脉血液动力学不同于正常冠状动脉血液动力学,近心端壁切应力及壁切应力梯度的变化要远大于远心端,从而对动脉管内皮细胞产生重要影响,这可能是心肌桥壁冠状动脉近心端易发生动脉粥样硬化的血液动力学机理。     

离心血泵内部流场数字模拟及溶血分析

血泵是心脏辅助循环装置的核心部件之一,其运行过程中所产生的血栓和溶血超出安全范围将会引发多种并发症,严重者甚至危及病人生命,因此血栓和溶血问题是衡量血泵性能的重要指标也是血泵的重要研究课题。研究表明,溶血主要是由血泵内叶轮的机械运动及血液的复杂流动的高剪切力引起。因此溶血多出现在血液与固壁接触面上及复杂流动的流体问。本次研究的目的是要探索用数值模拟的方法分析离心血泵内部的流场及溶血情况,在研究中通过与上海某医院合作实验采集一种叶片式离心血泵运行过程中的实验数据,再对该叶片式离心血泵内部流场进行数值模拟,通过对比血泵实际运行情况与数值计算结果对其内部血栓和溶血问题进行系统的分析研究,最终数值模拟分析的情况与该血泵在实际运行中的血栓和溶血情况基本相符。通过本次研究探索用数值模拟的方法对血泵的血栓和溶血现象进行分析,特别是对溶血现象进行一定程度的定量分析,此分析结果及分析方法可为血泵优化及临床应用做方法指导之用。     

混流式血泵的数值模拟及性能分析

轴流式血泵转速过高、离心式血泵容易产生流动死区是造成血液损伤的重要原因,而混流式血泵能有效缓解轴流式血泵的转速过高以及离心式血泵的流动死区问题。基于此,本研究旨在探究闭式叶轮混流式血泵的性能效果。通过数值模拟的方法对闭式叶轮混流式血泵进行数值模拟,分析该类型血泵的流场特性及压力分布情况,探讨其水力性能以及可能对红细胞造成的损伤程度,并与半开式叶轮结构混流式血泵的数值模拟结果进行性能对比。结果表明:本研究中的闭式叶轮混流式血泵具有良好的性能,能够安全高效运行。该泵在5 L/min下能够达到100 mm Hg的扬程,血泵内流动均匀,没有明显的涡流、回流以及流动停滞现象,压力分布均匀合理,可有效地避免血栓;溶血指数平均值(HI)为4.99×10^-4,具有良好的血液相容性;与半开式叶轮混流式血泵相比,闭式叶轮混流式血泵扬程和效率更高、溶血指数平均值更小,且具有更好的水力性能及避免血液损伤的能力。通过本文研究结果,或能为闭式叶轮混流式血泵的性能评价提供依据。     

应用CFD对人工血泵流场进行数值仿真

发展人工心脏以便在某些情况下代替心脏进行供血已成为医学界的普遍要求。血泵研制和改进中所面临的主要难点之一是血液在血泵中的流动分离等复杂流动情况 ,对人工血泵中血液的流体动力分析是发展先进人工血泵的前提。本文应用计算机求解三维Navier Stokes方程 ,对某型血泵叶片通道间内部流场进行了数值仿真。研究分析结果表明 ,血泵中流体具有非常复杂的流动情况。为避免流动中分离造成流体升压比下降和血细胞破坏 ,对通道的进口和小叶片的安放位置以及叶片高度的变化都提出了很高的要求。充分应用计算流体力学的发展来推动人工血泵的研究具有非常广阔的前景     

Computational fluid dynamics verified the advantages of streamlined impeller design in improving flow patterns and anti-haemolysis properties of centrifugal pump

Computational fluid dynamics (CFD) technology was applied to predict the flow patterns in the authors' streamlined blood pump and an American bio-pump with straight vanes and shroud, respectively. Meanwhile, haemolysis comparative tests of the two pumps were performed to verify the theoretical analysis. The results revealed that the flow patterns in the streamlined impeller are coincident with its logarithmic vanes and parabolic shroud, and there is neither separate flow nor impact in the authors' pump. In the bio-pump, the main flow has the form of logarithmic spiral in vertical section and parabola in cross section, thus there are both stagnation and swirl between the main flow and the straight vanes and shroud. Haemolysis comparative tests demonstrated that the authors' pump has an index of haemolysis of 0.030, less than that of the bio-pump (0.065).     

Computational fluid dynamics verified the advantages of streamlined impeller design in improving flow patterns and anti-haemolysis properties of centrifugal pump

Computational fluid dynamics (CFD) technology was applied to predict the flow patterns in the authors' streamlined blood pump and an American bio-pump with straight vanes and shroud, respectively. Meanwhile, haemolysis comparative tests of the two pumps were performed to verify the theoretical analysis. The results revealed that the flow patterns in the streamlined impeller are coincident with its logarithmic vanes and parabolic shroud, and there is neither separate flow nor impact in the authors' pump. In the bio-pump, the main flow has the form of logarithmic spiral in vertical section and parabola in cross section, thus there are both stagnation and swirl between the main flow and the straight vanes and shroud. Haemolysis comparative tests demonstrated that the authors' pump has an index of haemolysis of 0.030, less than that of the bio-pump (0.065).     

High-Resolution Fluid–Structure Interaction Simulations of Flow Through a Bi-Leaflet Mechanical Heart Valve in an Anatomic Aorta

We have performed high-resolution fluid–structure interaction simulations of physiologic pulsatile flow through a bi-leaflet mechanical heart valve (BMHV) in an anatomically realistic aorta. The results are compared with numerical simulations of the flow through an identical BMHV implanted in a straight aorta. The comparisons show that although some of the salient features of the flow remain the same, the aorta geometry can have a major effect on both the flow patterns and the motion of the valve leaflets. For the studied configuration, for instance, the BMHV leaflets in the anatomic aorta open much faster and undergo a greater rebound during closing than the same valve in the straight axisymmetric aorta. Even though the characteristic triple-jet structure does emerge downstream of the leaflets for both cases, for the anatomic case the leaflet jets spread laterally and diffuse much faster than in the straight aorta due to the aortic curvature and complex shape of the anatomic sinus. Consequently the leaflet shear layers in the anatomic case remain laminar and organized for a larger portion of the accelerating phase as compared to the shear layers in the straight aorta, which begin to undergo laminar instabilities well before peak systole is reached. For both cases, however, the flow undergoes a very similar explosive transition to the small-scale, turbulent-like state just prior to reaching peak systole. The local maximum shear stress is used as a metric to characterize the mechanical environment experienced by blood cells. Pockets of high local maximum shear are found to be significantly more widespread in the anatomic aorta than in the straight aorta throughout the cardiac cycle. Pockets of high local maximum shear were located near the leaflets and in the aortic arc region. This work clearly demonstrates the importance of the aortic geometry on the flow phenomena in a BMHV and demonstrates the potential of our computational method to carry out image-based patient-specific simulations for clinically relevant studies of heart valve hemodynamics.     

Three-phase CFD analytical modeling of blood flow

The behavior of blood cells in disturbed flow regions of arteries has significant relevance for understanding atherogenesis. However, their distribution with red blood cells (RBCs) and leukocytes is not so well studied and understood. Our three-phase computational fluid dynamics approach including plasma, RBCs, and leukocytes was used to numerically simulate the local hemodynamics in such a flow regime. This model has tracked the wall shear stress (WSS), phase distributions, and flow patterns for each phase in a concentrated suspension shear flow of blood. Unlike other computational approaches, this approach does not require dispersion coefficients as an input. The non-Newtonian viscosity model was applied to a wide physiological range of hematocrits, including low shear rates. The migration and segregation of blood cells in disturbed flow regions were computed, and the results compared favorably with available experimental data. The predicted higher leukocyte concentration was correlated with relatively low WSS near the stenosis having a high WSS. This behavior was attributed to flow-dependent interactions of the leukocytes with RBCs in pulsatile flow. This three-phase hemodynamic analysis may have application to vulnerable plaque formation in arteries with in vivo complex flow conditions.     

基于CFD技术的Sarns离心式血泵流动特性分析

目的应用专业计算流体动力学（computational fluid dynamics,CFD）分析软件FLUENT,对一种具有长短叶片的Sarns离心式血泵的内部流场进行三维数值模拟。方法利用Solidworks软件对Sams型血泵进行三维建模,然后对所建模型网格处理,通过选取标准,κ-ε湍流模型和SIMPLE算法,具体分析了内部流动状态、压力分布、壁面剪切力等流场特性。结果结果表明,该离心泵内部流场分布较不匀,叶片及血泵出口处有回流和旋涡现象,剪切力大小基本处于致红细胞破碎的临界状态之下,高转速下剪切力最大,主要分布在叶轮区域,但暴露时间极短,基本满足血液生理要求。结论该研究为Sarns血泵的进一步优化提供了理论基础。     

股动脉双路搭桥的血流动力学仿真

在传统股动脉搭桥术中，由于下游缝合区采用“端对侧”的“单路搭桥”缝合方式，移植管中血流会对缝合区底面产生很大冲击，引起局部血流动力学急剧变化，并可能因此而导致血管再狭窄和手术失败。由于缝合区几何结构的不对称必然导致流场的不均匀，本研究提出了“对称双路搭桥”的构想以图改善血流动力学。本研究对“单路”和“对称双路”两种连接模型中的血液流动进行了数值模拟。两种模型利用相同的几何参数进行建模，并采用了相同的边界条件。数值模拟结果包括流场、壁面切应力及其梯度等血流动力学参数。研究表明，“对称双路”模型比“单路”模型具有较大的纵向速度、较小的二次流、较均匀的壁面切应力等。因此，“对称双路”搭桥模型具有更好的血流动力学，可以减少股动脉搭桥术后内膜增生和再狭窄的可能性。     

附带局部突起的主动脉弓动脉瘤的血流动力学仿真

目的：为了弄清楚顶部附带局部突起的主动脉弓动脉瘤的血流动力学特征，因为针这种动脉瘤的血流动力学目前还较少有人研究。方法：建立了理想化的动脉瘤模型。利用计算流体力学的方法对模型中的生理性血液流动进行了仿真。结果：对流动情形、压力和壁面切应力分布进行了分析，以便评价血流动力学对动脉瘤的发展和破裂的影响。来自动脉的血流对下游瘤口和瘤顶局部突起的冲击较大。瘤顶局部突起区域的压力较高。在瘤口和突起口部位的局部壁面切应力比其他地方的要高。结论：下游瘤口和瘤顶局部突起部位是动脉瘤扩展和破裂的危险区域。     

Evaluation of the hemodynamics in straight 6-mm and tapered 6- to 8-mm grafts as upper arm hemodialysis vascular access

The present study is intended to investigate and compare the hemodynamics in two different sizes of hemodialysis arteriovenous grafts for upper arm hemodialysis vascular access: 8-mm tapered to 6-mm at the arterial side and straight 6 mm. A computational simulation approach is presented for this study, which is validated against the available experimental and numerical pressure measurements in the literature. The imposed boundary conditions at the arterial inlet and venous outlet boundaries of the models are physiological velocity and pressure waveforms, respectively. Blood flow fields and distribution patterns of the hemodynamic indices including wall shear stress (WSS) as one of the major hemodynamic parameters of the cardiovascular system and spatial wall shear stress gradient (SWSSG) as an indicator of disturbed flow patterns and hence susceptible sites of lesion developments are analyzed and compared between the two grafts. The tapered 6- to 8-mm graft seemingly is associated with less disturbed flow patterns within the venous anastomosis (VA) and the vein downstream while benefiting from higher blood flow rates within. Also, it shows a definitive advantage in terms of WSS and SWSSG distribution patterns around the VA and throughout the vein downstream with significantly lower values, which reduce the risk of thrombosis formation and stenotic lesion developments. The only disadvantage encountered in using 6- to 8-mm tapered graft is higher values of hemodynamic parameters at the arterial junction attributable to its significantly higher mean blood flow rate within. The results clearly indicate that the tapered 6- to 8-mm graft entirely outperforms straight 6-mm graft hemodynamically as an upper arm hemodialysis vascular access graft and confirms clinical data in the literature, which suggests advantageous use of tapered 6- to 8-mm grafts in the creation of upper arm brachioaxillary hemodialysis vascular access grafts in selected groups of patients with expectably higher patency rates and lower complications.